Alt kill switch planning (help) - Fuel Economy, Hypermiling, EcoModding News and Forum

California98Civic · 12-17-2011, 01:42 PM

I have been running without my alternator for a couple months. I just disconnect it, wrap the ends against water, and go. If I run too far or too low, I go through the slight pain of popping the hood and reconnecting. I want to plan and install a kill switch. I need help.

Where can I cut in for the splice for the switch without damaging the alternator? And can I do it at the fuse box inside the cabin? That would be much easier in terms of routing, but I doubt it is effective and safe for the alternator. Thoughts?

Here is, I think, the appropriate wiring diagram from the Honda Service Manual. I have checked all the wires and the color-coding matches. The wht wire is a heavy lone wire and the four others are bundled into a 4P connector [EDIT: The ECM/PCM ("ECU") is in the cabin]:

I am aware of Daox's mod, but I am uncertain of what line into the cabin I might safely use on my civic. The wht/red line from the 4P connector seems like a candidate.

California98Civic · 12-17-2011, 04:43 PM

Bump (with more information). As I study this today, I have gained a bit more information. In the diagram above the "wht/grn" wire leading from the voltage regulator is the ALTC ("Alternator Control") wire that leads to pin A19 in the ECU. The service manual says it "sends alternator control signal" from the ECU. The "wht/red" wire is the ALTF ("Alternator FR Signal") wire. The manual says it "detects the alternator FR signal." I do not (yet) know the difference. Anyone help? Which line, if either, do I cut into for my kill switch?

brucepick · 12-17-2011, 06:00 PM

For what it's worth -
Either the "wht/grn" or the "wht/red" - or both - is/are part of the ELD system (electrical load detection) that controls whether the alt runs at approx 14V vs. reduced voltage of about 12.5V. I believe that ALTC controls the alt's operation. ALTFR sends a signal back to the ELD, from which the ELD determines how to control the alt via the ALTC wire.

You should test the black/yellow wire. Pull fuse #15 in the underdash fuse panel, which powers that wire. This fuse also supports the vehicle speed sensor (VSS) so you won't want to drive with the fuse pulled. BUT it's a fairly quick + easy test to do. If the alt is deactivated by pulling that fuse, you've identified a wire that will do the job. If it disables the alt, you could cut that wire at the alt. Or, you could install a switch and a fuse, in line with the fuse box. But if you use that method, you would need to power the VSS separately.

Consider getting a second wire with plug that will connect to the alternator. From a junker car. If you end up wanting to sever a wire at the alternator that extra piece of wire harness can make the job easier.

Yes, I've been thinking about this too. So far, that's my only achievement on this one.

drmiller100 · 12-17-2011, 07:18 PM

There are only really two wires needed for the alternator to work.

The main battery lead (big wire) from battery to alternator I leave alone. If you unhook the Yellow/black which goes from the key switch to the alternator, and start the car, the alternator will not charge.

If you then give power to the yellow/black, the alternator will start charging. I have not tested to see if you shut the power off to the yellow black if the alternator will keep charging.

drmiller100 · 12-17-2011, 07:19 PM

the other wires I believe are signals to the ECU to increase the idle if a lot of electrical load is detected.

California98Civic · 12-17-2011, 08:02 PM

So if I cut the blk/yel wire for my switch, I will have in effect an on/off switch that will not damage the alt because I'm denying the field windings the power they need to fire up as well as the power needed to send/receive signals to the ECU? No damage will result if I test this maybe by pulling the blk/yel wire from the 4P connector at the alt?

drmiller100 · 12-17-2011, 08:25 PM

correct.

the only thing I am unsure of is if you cut the power with the engine running, it may not shut off the alternator charging until you shut the engine off (quit turning the alternator).

It will not hurt to test it.

One thing worth testing might be to hook the alternator black/yellow light to your brake lights. The brake lights themselves would act as a "sink" to collapse the field.
Hit the brake lights, and the alternator charges. Release the brakes, and the alternator shuts off.

deathtrain · 12-17-2011, 10:01 PM

Quote:

Originally Posted by California98Civic

So if I cut the blk/yel wire for my switch, I will have in effect an on/off switch that will not damage the alt because I'm denying the field windings the power they need to fire up as well as the power needed to send/receive signals to the ECU? No damage will result if I test this maybe by pulling the blk/yel wire from the 4P connector at the alt?

I see the its the blk/yel too. but do like you say and pull pins first before you start cutting in to it.

California98Civic · 12-19-2011, 01:24 AM

Quote:

Originally Posted by deathtrain

I see the its the blk/yel too. but do like you say and pull pins first before you start cutting in to it.

Tried pulling the wire tonight but got shy about yanking the line. I think I want to try the pulling experiment only after I find where the wire enters the cabin. I'll pull it there.

So, I traced the blk/yel through the engine harness to the connector where it changes color and then enters the engine bay. Eventually, I'll do a write-up once I get it all figured out. Right now, here is the engine bay wire harness diagram. In the upper right, see C101. That is the connector near the grommet to the engine bay. Numbers T101 and C104 below C101 are for the power line from alt to batt and the 4P connector.

drmiller100 · 12-19-2011, 01:38 AM

ok. you are making this pretty complicated.

there is a big round plug with a bunch of wires on the back of the alternator. Unhook the round plug completely.

Notice you can use a standard spade connector to hook one of the wires up on the back of the alternator. Using a piece of wire with a spade connector, hook up the terminal which the black/yellow wire used to be connected to. Using a male spade connector, hook the other end of the jumper to the correct spot on the round plug.

Now start the car, and notice the alternator is charging by watching a volt meter hooked to the battery.

Now unhook the spade connector. Does the voltage drop?

You only need two wires to make the alternator charge - one wire to the battery, the other through ignition, through the "charge light" on the dash.

The rest of the wires are a bunch of crap for the ecu to sense load to keep the car idling.