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

[California98Civic]

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.


2) Identify and cut yel/blk wire an inch or two from the 4P connector.


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).


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.


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

8) Connect wire to switch using female spade connectors.


9) put panel and installed switch back into dashboard.


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.

[brucepick]

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?

[California98Civic]

Originally Posted by brucepick

A very nice writeup indeed, with very clear photos. Nice job.

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.

Originally Posted by brucepick

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?

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

Originally Posted by brucepick

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?

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.

[cbaber]

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!

[California98Civic]

Originally Posted by cbaber

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

[steffen707]

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".

[drmiller100]

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.

[steffen707]

Originally Posted by drmiller100

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.

[steffen707]

Originally Posted by California98Civic

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

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?

[California98Civic]

Originally Posted by steffen707

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 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).

Originally Posted by steffen707

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.

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.

Originally Posted by steffen707

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 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.