How to Install an alternator cut-off ("kill") switch on a 1998 Honda Civic
 

Several Ecomodder members and many others have installed alternator "kill" or "cut-off" switches on their cars. “MetroMPG” tested and reported the potential fuel economy improvements "going alternator optional" on his Metro. “Daox” has a very good installation post for his Paseo. Some others have posted install DIYs for older Civics. On my 1998 Civic it seems a little trickier than it is on some other cars. This "how to" will outline how I did it, thanks in part to advice from “drmiller” and “brucepick”. Comments, corrections, and tips for improvement are all welcome. I will edit this post as appropriate, based on feedback.

BENEFIT OF 3-5% IN FUEL ECONOMY FOR 1998 CIVIC DX COUPE

The Civics have a "smart alternator". Through four wires running from the on-board computer (ECU) and the Electronic Load Detector (ELD) to the alternator, the sixth gen Civic applies a logic that modulates how much power the alternator produces, maximizing potential fuel savings by generating electricity when it will have the least negative effect on fuel economy and power. By deleting my alternator entirely and recharging the battery exclusively by plugging the car in at night, I have periodically observed a 3-5% increase in fuel economy over the last four or five months. This mod allows me to have that advantage, while still allowing me to revert to stock operations with the flick of a switch whenever I need more range.

ACHTUNG! ERRORS YOU GET TO AVOID BECAUSE I MADE THEM ;)

1 - You must disable two of the wires to the 4P connector, not just one: the sixth gen Civic's "smart alternator" has a four wire connector (a "4P" connector) and a separate large gauge white power wire for the alternator's power output to the battery. On the connector, one wire is for the charging light signal (blu/wht), another is the power line (blk/yel) for the field windings, and the two others are signal and control wires to and from the ECU. If you cut only the power line (blk/yel) the alt will still power using the blu/wht charging lamp wire. I know this because I tested for it using short wires with male and female spade connectors. I interrupted one line at a time and then two at a time until I was able to shut the alt off. You must interrupt both the blu/wht and blk/yel lines. A similar discovery was made by "busypaws" for his 1997 Protege DX alternator switch (he resolved the problem differently).

2 - You will have to cut into the blk/yel wire at the 4P connector: It will not seem ideal to cut into the wire at the 4P connector into the alternator. So you might be tempted to try to cut into the wire closer to the fire wall. The Honda Service Manual wiring diagram for the alternator might encourage you to think that you can cut in near the fire wall or in the cabin. I tried that. I cut a wire that also disabled an O2 sensor. The only way to avoid affecting other components on the harness in to cut in at the 4P connector.

SUPPLIES
(1) Butt splice connectors
(2) Two female spade connectors
(3) a few feet of adequate gauge wire
(4) a wire hanger
(5) an on/off switch capable of handling just a couple volts
(6) an exact-o-knife and a box cutter
(7) duct tape
(8) philips head screwdriver.

STEPS
1) Locate alternator and its light-green 4P connector, and unplug it.
http://ecomodder.com/forum/attachmen...4&d=1329095773

2) Identify and cut yel/blk wire an inch or two from the 4P connector.
http://ecomodder.com/forum/attachmen...5&d=1329096060

3) Connect your switch wire to each end using the butt splices.

4) Unplug blu/wht charging light wire at connector (on the left in the pic below).
http://ecomodder.com/forum/attachmen...6&d=1329096143

5) Cut a slit into driver's side firewall grommet using the exact-o knife.

6) Run switch wire through the grommet by taping it to the wire hanger.
http://ecomodder.com/forum/attachmen...7&d=1329096156

7) Cut hole into dash panel and run wires through it.

8) Connect wire to switch using female spade connectors.
http://ecomodder.com/forum/attachmen...9&d=1329096177

9) put panel and installed switch back into dashboard.
http://ecomodder.com/forum/attachmen...0&d=1329096187

Done!

BRUCEPICK’S ALTERNATIVE:
Brucepick came up with a clever alternative to cutting into the harness. He went to a junkyard and got a junker’s 4P connector and attached it to the existing connector on his car using spade connectors. With one connector essentially plugged into the next, he need not alter the wiring harness on his car at all. Pretty clever.

A very nice writeup indeed, with very clear photos. Nice job.
(What you probably don't know is that I used to earn my living taking photos.)

Well, in truth -
I bought the connector but haven't yet gotten around to splicing it into the system. Too d**m cold here right now in New England.

Cali98, your post corrects a misunderstanding I had -
I thought I needed to interrupt and provide switches for both the yellow/black and the blue/white wires. But it looks like you disconnected the blue/white and left it that way - right?

I think if I switch both wires on + off simultaneously (using one DPST switch), the alt/battery warning light would still work if the alternator fails one day?

Thanks. This post has been a while in the making. I bought the switch months ago. Some of the pics are more than a week old.

That's correct. I merely disconnected the blue/white line at the pictured connector.

That's correct, but I don't expect I'll need the charging light. I expect my voltage meter to tell me all I will need to know about the health of the alternator.

Did you buy an upgraded battery? I am thinking about doing this but I am worried about what happens when you cut off the alt. at night. I know that when I FAS my car at night the headlights dim a little bit as well as interior lights due to the decreased voltage. How long do you drive at a time with the alt. off? Do you drive at night with it? How long of a range does the battery have without alt support under normal loads? Thanks!

This mod is part of a series of mods, still not all completed, meant to rearrange how the car creates and uses electricity. I got a deep cycle battery. And I reduced electrical load with five LEDs for braking and running lights. I switched from the stock headlight bulb to HID bulbs (reducing wattage required). I bought a 6 amp battery maintainer, installed in the car, and I charge the battery at night by plugging in at the bumper. Some other minor changes. The last big change will be solar panels. If I had had those today, the car would have fully recharged during working hours, and I could have driven the 12 miles home with ease, even with the lights on. As it is, I had to use the alt for much of the ride home so as to protect battery life.

I hope that helps. Load reduction and a deep cycle battery are the key minimum things to do in order to maximize the benefit of the switch.

james

I'm so glad I found this thread. Just the info I need.

I'm planning to use a double pull double throw (dpdt) switch with center "off" to tap into the 2 wires you mentioned. On one side of the switch i'll connect the wires back to the splice so that it operates as "normal". On the other side, i'm going to connect the 2 poles to another DPDT micro switch that is activated when the gas pedal is fully Un-pressed (no throttle input) to go back to the splice.

So either the alternator will not work, "off positon", it will work as normal "up position", or it will only work when the engine is at idle/coast down situations "down position".

If a guy got creative, use the brake light to turn on the alternator - when the brakes are on, the alternator is on.

If a guy got REALLY creative, there is a TPS sensor wire which indicates idle. If the driver lets off the throttle and is coasting, turn the alternator on. You would have to use a diode, transistor, relay or something to not backfeed the wrong signal to the ECU.

If a guy got REALLY creative, have it come on automatically if the voltage drops below some set number - like 12.1 volts or something.

My microswitch connected to the gas pedal or throttle body butterfly solves your 2nd creative idea. And I believe they have voltage window switches that will send power or ground if a certain scenario is met.

Can probably find some kind of voltage floor switch, so if it falls below X volts it will provide power or ground. Couple that with a double pole, double switched relay and you're set.

Hey, i've got a 96 civic hatch, same Gen as your 98 and I've heard people say that even with the 4 wire connector plug removed, the alternator will still output 14 volts through the large white "charging" wire. Have you tested the volts after you switch it off?

I've got a 96 hatch with a d15z1 lean burn motor in it, and there just isn't enough power in lean burn at 65mph for me to hold that speed. I'm thinking that killing the alternator might give me that boost I need.

Also do you know if using a large relay on the white charging wire and just disconnecting it can harm the alternator if the field is energized?

I have a dash mounted volt meter. Unplugging the 4P plug will always keep the alt completely off. It cannot power-up itself through the thick white charging wire to the battery. My switch disables two of the wires in the 4P connector. If the alt is running and I cut the switch, the alt still charges until I cut the injectors and bump start again. But according to some, a small light on the line can drain the residual charge in the field windings (I have not tried this).

You might try taking the powr steering belt off as a test of this idea. It's easier than an alt disable and completely reversible.

I believe the answer might be yes, because the alt will be generating power with nowhere to go. But why would you want this? The power generation itself would still be a parasitic draw on your engine.

I hope those answers help.

My thought was that if you switch off all 4 wires and the main charging wire, so all 5 wires, then the alternator should shut off. I wanted to be able to do this on the fly so I don't have to go under the hood to reconnect anything, or bumpstart the car, even though bumpstarting isn't a huge pain.

My car doesn't have power steering.

So that's why people put the small light on the field winding wire, to drain the field windings of the electricity so it totally stops.

I have a 96 Tercel, I have not done any kind of alternator mod but I do have an idea of how long my car will run with a dead alternator. My commute to work is 15-18mi each way (depending on path). I can run my car back and forth at least 3-4 days before the battery is weak enough to cause a problem. It took me a few weeks to get it all straightened out becasue I got a defective replacement alt from the parts store and I didn't have time to swap it out again.

My problem with this type of mod is that Energy = Energy. If you are not charging your battery using the alt, and you charge it from the grid you are still paying for the energy on your electricity bill instead (likely at a "cheaper rate").

Also isn't a battery charger plugged in to a car battery for 8-10hrs at a time going to waste energy once the battery is "full". Kind of like people complaining about leaving cell phone chargers plugged in 24/7 even if they are not charging the phone.

Yes I can see that if you are able to maintain the battery with a solar panel you are ahead of the game.

From my understanding of the civic charging system and batteries/alternators is that, oh at one time I was really interested how the ELD system worked exactly I could be wrong, Is it more or less will turn off the alternator if the charge is below X (unkown to me) under 40mph and less than 10amp of electrical load.

I was thinking and someelse brought it up in a forum as to why the strategie wasn't used all the time, say at 60mph freeway speeds. I'd love to see the results of this system being utilized 100% of the time.

from being a mechanic I see how batteries act. if you do a deep charge, like say 20 or less amps for say 2 hours. when you come back to test you'll usually see something like 13. high 12 volts. surface charge. you could be using that to when cycling the alt. on and off.

another question or curiosity would be hooking up a voltmeter to see honda's strategy in action under 40 mph with no elec. loads on. or hooking up an amp clamp and seeing if with all loads off how much amps are being used. usually most cars I hook a VAT to are in the 15-20 amp range or more

If you get a good charger it will go into "maintain mode" and only give short bursts of power to keep the battery topped up. I have one of those "killowatt" appliance testers that plug into your wall and then you plug your appliance into it. I can test what the drain over a few days will be for you, because I have an on board maintainer for my CRV as it sits outside in the cold most of winter, and I rarely drive it. The maintainer works flawlessly, and in the dead of winter i hop in, and it fires right up, so I know the maintainer does its job.

Will this work with my four wire 1991 civic alternator?

The stock civic alternator has wire to turn the voltage down to 12v... basically shut off until needed, especially with a AGM battery which has a higher discharge voltage than a flooded.

Unfortunately I don't know which wire, but it goes to the ECU, and is grounded to shut off the alternator. You can just ground it with a switch to force shutoff (the ECU controls it with an open-collector circuit). I did this when I had a '94 civic. You can even monitor if the ECU has shut off the alternator by looking at the voltage: it's about 7 volts normally (you might need a 5k ohm load or so to see this), but about 0 volts when shut off. The ECU-controlled shutoff is fairly rare: it has to be warm, with no lights or fan on.

As we have been discussing, this wire you're talking about is the alternator charging control wire. When grounded it doesn't shut off the alternator entirely. It still is charging, but at a very low rate.

from the peanut gallery, there are two wires which cause the alternator to charge, just like every other modern car.
the great big wire which goes to the battery and carries the juice, and a "trigger" wire, yellow/black which excites the field and kicks it off.

The rest are signal wires from the alternator back to the ECU which the ECU uses to keep track of how hard the alternator is working. For instance, at idle, if the driver turns the heater fan on high and rear defroster, there is more load on the alternator, so the ECU needs to QUICKLY give a touch more air to the idle so the engine doesn't slow down or die.

for your purposes, the signal wires are not really needed.

I basically agree, but remember that I have disabled only two of the signal wires, not the large gauge charging wire to the battery, and I can still completely cut-off the alternator. I put my switch in the off position and when I restart the engine with a "bump" or "roll" start, the alt is not on anymore. And it has never come back on in 7 months since unplugging the alt and the two or three months since completing the kill switch project that starts this thread.

I learned, using a process of elimination method you recommended, that if I disabled only the blk/yel and left the wht/blu connected (for the "battery" light on the dash) the alt would come back on. When I studied the wiring diagram it seemed the battery light was able to give just enough power to the alt to fire it up on its own. I'm not fully confident I am correct about that because it is not what seems logical in terms of design, but it is what experiment showed me, so I have followed it.

While you are right, others have noticed that voltage can also come from the battery indicator light on the dash as well. I've also heard that if the car is running and you disconnect the yellow/black wire it will keep charging because the alternator already has the field charged up. Not sure on this cuz i havn't tested for myself. But i heard that if you ground the yellow/black wire from the alternator via a light bulb, it will slowly drain the field through the light bulb and then shut the alternator off.

While it sounds black and white, there's been several attempts and discoveries in this regard with mixed results. I'm simply trying many methods and reporting my discoveries so others don't have to.

Yeah, sometimes its just easier to do what you "KNOW" works, than what makes sense. I don't know if I'm going to do all 4 wires or just 2 of them like you did California, but I charged the battery last night from 12 volts after 3-4 days to 12.8 with my charger connected to my killowatt power reader, and it said it cost me like 8cents to charge it. Now I gotta do some calculations to see if its worth it.

My calculations are as follows
$0.10 / 3days * 365days per year = $12.16 per year
$12.16per year / $4 per gallon = 3.0416 gallons I could buy with that $12.16 cents if I didn't spend it on electricity.
3.0416 gallons * 45miles per gallon = 136.8 miles I could drive on that gasoline
136.8 miles / 1.8miles per gallon increase = 76 gallons needed to be used to equal things out. So as long as I drive more than 45miles per gallon * 76 gallons = 3420miles in that year of paying $12.16 for electricity, I will be better off.

I didn't take into account the possibility of killing the battery earlier than normal, and I know I could have just compared the 8-10 cents it cost to charge to what mileage I actually did drive and gallons I did use in the last 3 days; however, I was doing a ton of tests, that gave me horrible MPG over this past week.

I'll try and do some more calculating after I stop messing with the car for a while.

Actually i got bored and tried the other calculation. If it cost me $0.10 to charge up the battery and gas costs $4 per gallon. I could have bought .025 gallons of gas, at 45mpg I could have driven 1.125 miles. Divide that by my increase in gas mileage of 4% of 45mpg is 1.8. Which is .625gallons at 45mpg is 28 miles. So as long as I drove 28 miles that $0.10 cent charging cost was worth it.

I know I drove at least 70 miles, so i'm ahead, right?

Try using the http://ecomodder.com/forum/images/em...ttons/edit.gif feature to update your previous posts, rather than making posts one after the other. Keeps the info more organized and easier for people to read these threads.

I get what you're saying, but having all 3 posts combined into 1 large post makes it harder to read through. If you break up the posts then it gives a natural break in the information.

Otherwise this whole thread would be one long run-on paragraph.

I don't know if anybody still makes one (because I've been out of the car audio game for a while now) but in the late 90's my friends neighbor had a rather large sound system in his GMC jimmy. He had an alpine alarm that monitored the voltage of the battery and if it dropped below 12 v it would start the truck and recharge it to 14 v. We could probably learn more about the monitoring system to adapt an automatic setup with an over ride incase ti decides to not work while driving.

so then your able to go 70 miles on a fully charged battery without an alternator?

you still have to take into consideration paying off the deep cycle battery. by any chance did you buy the highest reserve capacity battery you could fit in the car?

The honda charging system is supposed to do this, but from my understanding it's limited. I've never had an actual voltmeter in my car to even look and see what the computer is doing.

I was able to go 70miles but that was in low charging mode, not "no charging mode".

I havn't purchased a deep cycle yet, I wanted to test it out first.

Info on ELD and stock fuel saving behavior
 

Summary of what ELD does, from secret way to gain a bit more mpg - Honda Civic Forum
------------------

The civic computer instructs the alternator to drop from 14.5 volts to 12.5 (ie. not charging the battery) when all of the following are true:

- Load below 10A
- Speed below 40 MPH
- Engine speed below 3600 RPM
- Coolant temp above 140 F
- A/C off
- Intake air temp above 65 F
- Brake switch off
- Fuel cut-off not active


In other words, the alternator is essentially "idling" when the load on it is low, the car is warmed up and being driven gently. Note that the alternator reverts to normal charging when braking or decelerating (fuel cut-off mode), which is like a simple form of regenerative braking found in modern hybrids and electric vehicles.
------------------

I myself have taken out the ELD, so whenever the engine is on, a bit over 14V are at the battery posts. I feel as though this will help increase the life of a regular lead acid battery, as it's being charged whenever I'm driving. Especially good in winter. I managed 36.6MPG on a trip to the beach in my 99 Civic DX auto with the ELD removed.

Do you think it eats much fuel? The alternator isn't working very hard to keep the battery at 14.2V.

EDIT: I don't think Canadian Civics have an ELD

This isn't entirely true, when the ecu grounds the alternator control circuit "C" wire, the alternator does drop to 12.5 volts, but it is in fact still charging. I tested this with an almost dead battery that couldn't start the car. I jumped it and while grounding this "C" wire the car ran just fine.

Yeah, I knew the alternator doesn't shut off completely, just is more passive or set at a lower voltage goal. that quote was from 'gearbox' of civicforums.

It has been shown to increase mpg by 10% to eliminate the alternator. I would say that running it all the time by eliminating the eld would probably use a little more fuel then it already does in normal mode, but probably not much.

I can only simply offer my experience running without the alt since last September. The mod in this thread shuts the alt off completely if after flipping the off switch you cut the engine and bump start. Or if you never turn the alt on in the first place. The biggest gains are on the freeway, or any other driving over 40 mph, which is a condition when the ELD normally has the alt charging at 14.3 volts or so (full on). This means I can use the freeways more, get places quicker and still top 60mpg and more. That's my experience.

has anybody figured out how much this will cost ? how much battery capacity do you need, and how far can you drive at night? what brand deep cycle battery will you use? how long will they last?
what kind of charger? these are a lot of questions, but till they are answered, you really don't know how long it will take to pay for this mod. You also have to remember to charge it, and then unplug the charger. seems like a lot of work and cash for very little gain. Being able to turn your alternator on when you need it is nice, but will negate any fuel savings.
what about just replacing your alternator pulley with a 5 percent larger pulley. would this take some load off the alternator, without the extra expense and hassle of disconnecting your alternator?

From a strictly financial standpoint one needs to compare their current mpg with the guesstimate of 10% improvement. in 10,000 miles from 50old to 55new mpg you would save $73 dollars at $4 per gallon gas used.

in 10,000 miles from 30mpg to 33mpg you would save $120.

These figures are without the cost of charging deducted from the annual savings as that is a continual annual cost, and not an up front cost of say the batteries, charger, wire, switches, ect.

SO MANY VARIABLES..............

I use an Odyssey PC1200 deep-cycle battery and the 6amp Odyssey charger (total cost was near $280). The set up might last 5 years or more, with care. The cost of the switch and wire was negligible. I figure it will take about a year and a half "to pay for itself".

That's fair. I think of it maybe a little differently than a lot of people on this site (but not all, I'm sure). I don't modify my car and hypermile it primarily for direct and immediate cash savings, though I have managed to come out ahead so far. I get satisfaction from boosting this 1998 car of mine to 60+ mpg and I get a sense of autonomy from not being beholden to the automakers' pricing of new high-MPG vehicles. You are comparing the cost of the mod to direct savings from the FE improvement, but I'm partly thinking about my savings as coming from the avoidance of car payments.

By my figuring, I'm slightly ahead in cost/benefits of ecomodding (mostly through hypermiling the car) and thousands ahead in avoided car payments this year.

I'm with you when it comes to buying a new car. I drive a 1984 crx. but I still can't help but wonder if you would be better off just running a slightly bigger alternator pulley. I am all for higher mpg, but only if it puts more money in my pocket.

Not letting "the man" hold you down calicivic? :)

This is a very good point about just taking an old car and modding it to get better mileage than you can get from a new car. You're saving a bunch by not buying a new car.

I've often thought about buying a 2nd gen prius and putting in one of those booster packs. Sure it'll cost like $4000 or somehting for the booster, but when compared to buying a totally new vehicle, i'm way ahead and can still get better mileage than any new "stock" car.

I've always been 10-20 years behind on owning a new car.

My questions is in a somewhat modern 88 or 92 or even a 96-00 civic are you even able to get the amps to 10 or less? Cause I've used a VAT on a lots cars to make sure there charging and I don't think I've seen a car with that low of amps at idle even with every possible accessory off.


Has anyone driven with a voltmeter hooked to the battery with no accesories at all on and seen the volts go from 14 to 12 in the driving conditions listed?

I thought about a system where I would have a cut-off switch for the alternator, (with a Volt meter to monitor battery power levels)

Then install a floor mounted push-button, on the floor about a foot behind the clutch pedal. If you go down a steep hill, or approach a stop, and use the engine compression to slow down the vehicle in stead of the brakes, you step on the switch, re-engaging the alternator. The alternator will then generate power from the "braking action" and not consume fuel.
You cannot step on it while the clutch is pressed.
--Obviously only applicable to manual transmission vehicles--

(accessories sold separately, batteries not included)