73 Interior Courtesy Lights
Thread Starter
Navigator
Joined: Nov 2016
Posts: 9
Likes: 2
From: Bellingham Washington
73 Interior Courtesy Lights
I am having problems with the interior courtesy lights. They stay on all the time.
I have replaced the switches, and they worked for a while but back to staying on all the time. I have disconnected both switches and the light still stay on.
1. Can anyone tell me how the wiring circuit works, the tiny wire to the switch does not run directly to the lamps, where does it go after the switch before the lamps.
2. I have only traced the switch wire and lamp wiring into the wiring harness, have not pulled out any of the wires in the harness.
3. It looks to me that the switch open with the door closed and closed with the door open, am I wrong?
4. I hate wiring issues, mechanical issues are much easier for me.
I have replaced the switches, and they worked for a while but back to staying on all the time. I have disconnected both switches and the light still stay on.
1. Can anyone tell me how the wiring circuit works, the tiny wire to the switch does not run directly to the lamps, where does it go after the switch before the lamps.
2. I have only traced the switch wire and lamp wiring into the wiring harness, have not pulled out any of the wires in the harness.
3. It looks to me that the switch open with the door closed and closed with the door open, am I wrong?
4. I hate wiring issues, mechanical issues are much easier for me.
Race Director
Joined: Nov 2006
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From: Sunshine Coast, Queensland, Australia
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Sounds like you need to get the genuine GM Electrical Troubleshooting Manual for your car. breaks down every individual circut. explains how every circut is supposed to work. where on the car different connectors will be found.
It will take the pain out of working on your wiring now and in the future. Most vendors sell them.
It will take the pain out of working on your wiring now and in the future. Most vendors sell them.
Burning Brakes
Joined: May 2013
Posts: 789
Likes: 129
From: Los Banos CA
I am having problems with the interior courtesy lights. They stay on all the time.
I have replaced the switches, and they worked for a while but back to staying on all the time. I have disconnected both switches and the light still stay on.
1. Can anyone tell me how the wiring circuit works, the tiny wire to the switch does not run directly to the lamps, where does it go after the switch before the lamps.
I have replaced the switches, and they worked for a while but back to staying on all the time. I have disconnected both switches and the light still stay on.
1. Can anyone tell me how the wiring circuit works, the tiny wire to the switch does not run directly to the lamps, where does it go after the switch before the lamps.
- there is always power going to the courtesy lights (so if you use a test light, you will see voltage in the light sockets, even when the bulbs are not 'on'). The reason that the bulbs don't light up in this state is that they don't have a ground connection.
- The two door switches and the headlight switch provide a ground path for the circuit. For the door switches, when the door is open, the switch 'closes' and provides ground. If you disconnected both door switches and the light stays on, then something else is providing a connection to ground. Either the headlight switch is bad (or it's in the 'on' position), or there is an open wire someplace that is touching a ground point.
Opposite for me, but I do OK with the mechanical.
Melting Slicks
Joined: Feb 2018
Posts: 2,327
Likes: 721
From: Marietta GA
You need to make sure that both under dash light bulb holders are screwed into their correct location. I would also check each bulb holder to make sure that the ground wire is not exposed, that will turn on the lights when touched to a metal part (causing a ground).
Thread Starter
Navigator
Joined: Nov 2016
Posts: 9
Likes: 2
From: Bellingham Washington
Thanks everyone, this give me a lot of good information to check.
I have checked the switches, actually removed both and I have checked the headlight switch and they stay on all the time no matter what. Still could be a bad headlight switch, did not think about that.
Now that I know that the switch completes the ground to the lamps start with the headlight switch replacement, worst case, re-wire the ground leg of the circuit.
I have checked the switches, actually removed both and I have checked the headlight switch and they stay on all the time no matter what. Still could be a bad headlight switch, did not think about that.
Now that I know that the switch completes the ground to the lamps start with the headlight switch replacement, worst case, re-wire the ground leg of the circuit.
Racer
Joined: Feb 2018
Posts: 254
Likes: 73
From: Chicago, Illinois
I had this same problem on my 76. It ended up being the cargo area dome light, one of the wires chafed where they pass by the support bracket. Where it rubbed through, it pulled the system to ground and kept the lights on. Took me a while to figure it out cause the lamps under the dash were fine and so were the switches and headlight switch. Just another thing to check.
Last edited by MGC/D_7601; Apr 21, 2021 at 12:08 PM.
Melting Slicks
Joined: Feb 2018
Posts: 2,327
Likes: 721
From: Marietta GA
When you rotate the headlight switch and can feel the resistance that occurs when the interior lights are supposed to come on, the switch might be ok. I just removed my speedo & tach, by far the most labor intensive, painful, and horrific repair work done on my car. Moving around a wiring harness that close to 50 years old is impossible. If you have a 73 factory service manual, the complete wiring schematic is located at the end of the manual. I can get you the color of the ground wire, if you don’t have a manual, let me know. The idea of a chaffed ground wire seems likely. The courtesy light wire is routed from the drivers kick panel, then under the door sill, and then above the rear wheel hump, terminating at the rear light. The passenger side courtesy light is routed behind the dash.
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Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
I suspect that a critical little detail is causing your problems. From the factory, there were some little rubber 'bumpers' stuck to the door/jambs where the switch heads are to make contact. If those are "missing" (adhesive dried out; washed off; removed by someone who didn't know what they were; etc), the switch will not "break" contact and the lights will stay on.
Last edited by 7T1vette; Apr 21, 2021 at 06:31 PM.