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I need electrical troubleshooting advice. (1982 marker lights & low beam)
I'm back into Stitch, my '82, and his marker lights and low beam don't work on the driver's (left) side. The high beam works. Everything on the passenger side is working properly. The brake lights work.
I've checked the usual suspects: Fuses, relay, bulb control unit. Everything seems good, and the left and right sides share fuses and relays anyway, so if one side was out the other should be out as well.
It's confusing, since it's everything on that side and it's different circuits. Is there a common ground for all of these that I should be looking at?
Last edited by Shawn Stanford; 10-09-2023 at 11:00 PM.
Okay, I nosed around with a Google search and found this thread: https://rennlist.com/forums/928-foru...ng-lights.html . It blamed the bulb control unit and recommended a work-around using jumpers between 1-9-12, 3-5, and 7-4 . It looked like this. When I did that, I got the rear left marker lights and the front left marker lights. That thread was for an '84, since I got lights on the left, I believe that I have a bad bulb control unit, and I don't have a pinout listing for an '82. I found an electrical diagram or something on the side of the unit, so I guess I'll try to figure out what it's trying to tell me.
Last edited by Shawn Stanford; 10-10-2023 at 12:24 PM.
A blast of contact cleaner on the pins and plug might fix it before you need to open the box and refresh the solder joints.
I already tried that. It's never the easy fix. But, what the hell, I'll try it again. I have a buddy with an '80 and an '81 that he's working on. I'll borrow one of the controllers and give it a try in my car before I go spending money on one off eBay.
Maybe you already have this info but just in case.
Fuses:
24 Headlight High Drivers
25 Headlight High Passenger
26 Headlight Low Drivers
27 Headlight Low Passenger
High and Low Headlights share grounds on each side so if you have high on drivers side ground should be good for low as well. Could it be just a bad bulb for the low beam drivers side? They each have their own fuses so check fuse 26 as well.
The other thread explains the marker lights pretty well.
I checked and I'm not getting power at the fuses for low beams or marker lights on the left side. I get 12v (and lights) on the fuses for the right side.
Last edited by Shawn Stanford; 10-10-2023 at 05:24 PM.
I checked and I'm not getting power at the fuses for low beams or marker lights on the left side. I get 12v (and lights) on the fuses for the right side.
Thats weird because the low beam fuses (26 drivers and 27 passengers) get power from the same headlight relay (XIX-XX) which is wire 56b on the schematic. Marker light fuses 28 and 29 both get their power from the light bulb control unit but according to the diagram they have different internal switches so one bad switch could take out the marker lights on either side of the vehicle.
I just spent the last three hours poring over the wiring diagrams and crunched into the footwell of the car with a multimeter. I think the problem is behind the panel.
For the marker lights, I checked both left and right circuits at the switch, and they both have continuity and 12 volts coming out. I checked at the input from the harness to the panel, and they both have 12 volts from the plug to the fuse output. I tested across the fuses and 28 has low voltage, 29 has 12 volts. I tested fuse input to the output plug that runs into the harness running through the firewall and the left circuit (gr/bk) has low voltage to the plug and the right circuit (gr/re) has 12 volts.
So, assuming I did this right (a yuge assumption!), I need to look at the back of the panel.
Last edited by Shawn Stanford; 10-10-2023 at 07:47 PM.
There still could be an issue with the bulb control unit. From the schematic it shows three internal switches which are probably transistors. I haven't opened one up. When you jumpered the connector as directed in the other thread, the marker lights worked, correct? If that's the case then there is probably an issue with the left side switching mechanism inside the light switch. I would still borrow one and try it before pulling apart the panel. The headlight not working is a separate issue.
Last edited by Flinstigator; 10-11-2023 at 09:01 AM.
The bulb control is for rear lights only. Fuses 28&29 receive power from light switch. Fuse 28 does supply power to bulb control terminal 7 for LR tail/marker and fuse 29 supplies power to terminal 5 for RR tail/marker.
The bulb control is for rear lights only. Fuses 28&29 receive power from light switch. Fuse 28 does supply power to bulb control terminal 7 for LR tail/marker and fuse 29 supplies power to terminal 5 for RR tail/marker.
I fixed my terminology above and light switch is what it should have said. According to the schematic there are several internal switches inside the light switch with one for the left side and one for the right side marker lights and the right side is working correctly but the left side isn't getting adequate power. I would check the wiring going into the light switch. Shawn, did you have the POD out on Stitch or was that the other car? Maybe the plug going into the light switch isn't making good contact or it's bad? I would unplug and DeoxIt. Shawn does the front side left marker light work? That doesn't appear to go through the lamp control module. You could jumper fuse 28 so it gets power from top of 29. If all your marker lights work as expected then the problem would be in the wiring or the light switch.
Okay, more time looking through diagrams and thinking about how to test. I am so ignorant when it comes to electricity, but I think I'm starting to learn, so there's some hope.
I found the wires into and out of the panel for the marker lights and the low beams. The marker light input from the switch comes into the CE panel at B3 and it goes to the wiring harness at M5. I checked for voltage at both these points and found 12 volts. I also checked with the switch on and off, and with the fuse 28 in and out, and I double checked the right side circuit to confirm my results and understanding. I'm getting 12v out of the CE panel at M5.
I have power through the panel, and wiring into the harness is tight and the contacts are shiny. I went into the left fender well and checked for power at the connector where it goes into the splitter for the side marker and parking light, and there's no power there. I didn't see any breaks or suspicious sections when I traced the wire bundle back through the engine bay to where it dives under the expansion tank.
There still could be an issue with the bulb control unit. From the schematic it shows three internal switches which are probably transistors. I haven't opened one up. When you jumpered the connector as directed in the other thread, the marker lights worked, correct? If that's the case then there is probably an issue with the left side switching mechanism inside the light switch. I would still borrow one and try it before pulling apart the panel. The headlight not working is a separate issue.
They are reed relays for the bulb monitoring. Indeed bulb monitoring is only on Rear Markers and Brake Lights.
Circuit 58L is for the rear light and rear side marker. That circuit comes off the marker light circuit after fuse 28 but before the M5 pin (which goes to the front of the car). Circuit 58L runs out of the S1 pin and into pin 7 of the Lamp Control Unit (LCU). It runs out of pin 4 of the LCU and to the back of the car.
I currently don't have those rear marker lights. I jumpered LCU pin 7 to pin 4 (and pin 5 to pin 3) and I have the rear marker lights. So, I've actually been chasing two problems with the markers, one of which is solved: I have a bad LCU.
I was talking about inside the light switch. I didn't know what was inside but upon further review they are just mechanical switches Light Switch. to send power from 30 to 58L 58R to M5 (left) and M6 (right) which run the front side marker and parking lights. 58R and 58L then proceed to the Lamp control unit to control the rear marker and rear side marker lights which are working on the right side but not the left. Shawn has power at M5 but not at T4g where it splits to power the left front side marker light and left parking light. M6 has power and T4h has power to power the right side. Do you have voltage at lamp control unit on pin 7 (gr/bk wire) or pin 5 (gr/rd wire). I'm guessing you will have power on pin 5 because that is the right side of the car where your lights are working. If you have power on M5 then you should also have power on pin 7 but those rear side marker and rear light aren't working.
If you unplug the lamp control until and turn the parking lights on do you have left front and side marker lights? Right side should be on
If you plug the lamp control unit back in and unplug T4g which is wire in left fender that goes to the left parking and side marker light do you have rear left side and rear left marker lights on?
When you jumpered the light control module in the 84 thread (1-9-12) brake lights, (3-5) rear right markers, and (4-7) rear left markers you said that all of your lights worked? You bypassed the light control module. If all of the lights worked properly at this point there may be a short in the left side of that light control module.
10-09-2023, 07:54 PM
I need electrical troubleshooting advice. (1982 marker lights & low beam)
