No headlights, TS, Brake lights…fog lights

[Mike7447]

I’m going crazy trying to determine the issue. Dash is currently out, but I’ve got the cluster switches and multifunction switch plugged in. 
the passing control relay under the dash is plugged in. The instrument panel is unplugged, and cannot be plugged in, I’ve hacked it up to customize the instrument cluster.
 

the issue is when I turn on the headlights, the doors raise, but no headlights, or passing control pop-up.

Interior lights, hazards, running and tail lights work.

ive checked 44x it clicks. I’ve pulled the passing relay, and jumpered the pin to simulate operation, again 44x clicks. I’ve ckd the fuses, and continuity on the fusible link for the headlights, all is good. 
when I probe the three pins on the headlight socket with it unplugged, there is 12v on one pin. When I plug the headlight in, there is 12v on all 3 pins. I am missing a ground signal. I’ve ckd that lug at the ground area on the passenger side inner fender wall, removed it, cleaned the area, and made sure it was tight.

i don’t know how or where this circuit flows to eliminate or bypass a damn relay. I am at a loss for where the ground signal even comes into the circuit, and why there is 12v on all 3 pins after I plug a headlight in.

if I turn on the fog lights, ( they don’t work) but with the headlight plugged in , and if I probe the pin on the headlight that should be ground using my test light,  the fog lights come on…

going crazy here….ive looked at that headlight circuit diagram so many times, I can almost see it in my head.

Edited November 30, 2024 by Mike7447

[BKB94]

Keep hooking up temporary grounds, Your on the right track.

[tux]

You can't run the fog lights without the headlights, unless someone modified the harness. 

 

The cars I've had all had some kind of harness modification.

 

If you've got more money and time than you have perseverance and time, I would recommend the route that didn't exist when I rewired.  get a PMU and be done with your electrical gremlins. I've been debating getting one anyway since many of our relays don't exist anymore

 

[psu_Crash]

I have the electrical diagram printed out and pasted together to make it "easier" to follow. I'll take a look when I get out there this morning and see if I have any pointers on a probable cause. 

Edit: Stating on page 178 of the electrical section in the service manual, it shows the ground points. Although I'm not seeing one called out for the headlights right away. 

Edited December 1, 2024 by psu_Crash

[Mike7447]

2 hours ago, psu_Crash said:

I have the electrical diagram printed out and pasted together to make it "easier" to follow. I'll take a look when I get out there this morning and see if I have any pointers on a probable cause. 

Edit: Stating on page 178 of the electrical section in the service manual, it shows the ground points. Although I'm not seeing one called out for the headlights right away. 

I do the same thing with the schematics and have the entire 3 page flow chart from the ecu all taped together.

the headlight circuit ground source looks to come from the headlight switch itself. I’m gonna cut into the two wires that are supposed to be ground, and tee a 14 ga. Wire. I’ll ground that to the column mount.

[Mike7447]

15 hours ago, tux said:

You can't run the fog lights without the headlights, unless someone modified the harness. 

 

The cars I've had all had some kind of harness modification.

 

If you've got more money and time than you have perseverance and time, I would recommend the route that didn't exist when I rewired.  get a PMU and be done with your electrical gremlins. I've been debating getting one anyway since many of our relays don't exist anymore

 

What is a PMU? I’m currently using a MS3 pro mini to control the engine.

* Edit, just googled it. Power management unit.

why this instead of a complete rewire? 
 

I had a 1987 car that I spent 40 hours wiring on, but the car had a v8 that ran on its own ecu as well. I have all kinds of handwritten “notes” in the service manual where I was hacking into the wiring harness to make the headlights and power accessories work, but don’t remember if I actually fully re-wired it.  At this juncture, I’m getting really close to doing that… the relays, that talk to relays, that talk to relays is just crazy.

Edited December 1, 2024 by Mike7447

[Mike7447]

Just to make sure I’m not wasting anyone’s time here.

* from my other post concerning the passing relay:

I figured out my headlight issue.

#1. I am an idiot.

i had the male headlight harness plugged into the wrong female socket.

unfortunately, I managed to kill the passing relay while trying to bypass junk. 
if all this thing does, is raise the headlight doors and allow me to flash someone I intend to pass, then I can forego using it. It appears a new one is about 100 bucks.

i know I can jumper headlight function simply by combining the blue/red, and the blue/yellow wire that goes to this relay and get the 95% function that I need, and when I decide to cough up a hundred bucks, unplug that jumper,I just want to be sure that’s all it does. 

[tux]

Just the way I'd do it if I had to again.

 

Kind of simplifies everything has everything in one spot