Electrical Test headlight switch

[Dontknowchit]

Just got done wiring the headlight switch pin out back to stock configuration. Previous owner had installed aftermarket fogs and rewired the switch to get them to work. Oddly enough he had taken the time to wire it to the fog light switch and you even had to have the headlight switch on to run them, jist like stock but the headlights did not work. He did however use spade connectors to connect to the original fog connector so the light side was unmolested.

After rewiring to correct configuration at the plug, the headlights do not turn on. (Likley why prev owner did it). The switch is not oem, definitely aftermarket.

Before throwing parts at it, can anyone instruct me on how to test the switch?

The flash to pass high beams work by pulling in on the turn signal. Signals and hazards work, so I know that the fuse is good, the bulbs work, and they have power.
I have a feeling it's the switch, but how to test?

 

[General karthief]

Different years have different switches and possibly wire colors, what year?

 

[Dontknowchit]

92 gt hatch, I used this:

 

[AeroCoupe]

Do the running lights and dash illumination lights come on? If so then the PINS 1, 3, 4, & 6 are good to go. If not then use a DVM and back probe PIN 6 with one of the leads and the DVM set to continuity (https://www.fluke.com/en-us/learn/blog/digital-multimeters/how-to-test-for-continuity). With the other lead to a known ground the DVM should beep. Next switch the DVM to measure DC voltage (https://www.fluke.com/en-us/learn/b...-measure-dc-voltage-with-a-digital-multimeter) and back probe PIN 3 to see if you have 12 VDC. With the head light switch pushed in one step for running lights back probe PIN 1 & 4. If you do not get power on these PINS but PINS 3 & 6 are good then its the switch or somehow the spade(s) on the wire(s) is not contacting the terminals of the head light switch.

For the head lights you know that PIN 3 and 6 are good so now with the headlight switch pushed all the way in back probe PIN 2 for 12 VDC. If you are not getting power then its the switch or again or somehow the spade on the wire is not contacting the terminal of the head light switch.

If you have power from the switch to the headlights then back probe one of the headlight connectors to see if you have 12 VDC at the head light. If you do then check the grounds at the head light.

This is just how I would do it and I am by no means an electrical guru but this stuff is not like wiring up a stand alone ECU.

 

[Dontknowchit]

Thank you so much. The side markers and dash lights were coming on with the fog lights when he had them wired that way. They are not now. I will follow your steps and report back!

 

[Dontknowchit]

Got some results but a little foggy as to what they mean. The plug plastic broke apart with the fiddling so I carefully plugged the spades directly to the pins on the switch. So I'm ordering a new pigtail anyway.

Running and marker lights come on with switch, however interior illumination does not. When pin 1 and pin 2 are jumped together with light switch depressed 2 clicks, the interior illumination lights come on. So I think that means switch for pin 1 is bad, right?
Pin 2, 3, 4, and 6 are good.

With the headlight switch depressed 2 clicks, no 12v on headlight plugs. And lights do come on with flash to pass turn signal lever pulled back.

So I think switch is toasty?

 

[AeroCoupe]

That would be my guess.

 

[Dontknowchit]

The mystery continues.....so I got the new pigtail and new switch from lmr and installed per directions.
First failure was backprobing pin 1 with headlight in one click. There was no power. There was good power at 4 on that step. Second failure is no power at headlights with switch all the way in. There was a previous electric fan install so I think I need to dive into the under hood harness to see what has been done.

Parking lights, turn signals, flash to pass all still work. So looks like switch and harness were good after all. In an attempt to "clean up" the engine bay the wire loom was routed inside the fender so looks like some body deconstruction to really take a peak.

 

[Dontknowchit]

OK well the fender is off and I honestly do not know where to look now. I expected to see a splice hack job in this bundle of taped up wires but there are none. If the flash to pass is working then I have to have continuity to the proper plugs right? I found these 2 plugs just hanging I think one is for fogs and one is for coolant tank, that right?

I'm happy to do the testing, Im already elbows deep but just dont know where to go with this....no 12v at the headlamp plug when lights switched on.

please help point me.

 

[Dontknowchit]

I got it! No way other than dumb luck and time. The previous owner had put the headlight feed wire into the dead plug on the ignition module. I had tried everything so I just started checking all the plugs behind the dash. I don't think the lights have worked since this engine was transplanted into this car!

The red with yellow stripe wire was supposed to be in the flash to pass module but had been pinned into the ignition plug!

 

[AeroCoupe]

Great job man!!!

 

[Dontknowchit]

So satisfying
This mystery was driving me crazy! One of those "it's all right, it ought to work" kind of jobs.