Interior lights permanently on. 67 GTO - Pontiac GTO Forum
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post #1 of 8 (permalink) Old 11-07-2016, 08:55 PM Thread Starter
 
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Interior lights permanently on. 67 GTO

OK, so I bought my beauty about a month ago. 21K original miles. However age is age and I am working through some issues. I fixed a rough engine (needed a new condenser). Slow convertible top (leak in a hydraulic hose, filled the resevoir) and now the interior lights. I noticed the night I brought the car home that the interior lights would come on when I hit the brakes. OK, a short I thought. I'll get to it. A couple days ago the fuse that powers the brake lights and interior lights burned out so I replaced it (20A) and surprise: the interior lights are now on permanently whether the brakes are applied or not.

This is what I have done so far: 1) taken both door switches out of the jams to remove them from the equation. No change. 2) disconnected the brake light switch under the dash. No change. I tried turning the interior light switch on and off several times to see if that would do anything. No change. Im at a loss as to the cause or even how to begin trying to find it. I read something about a ribbon cable short under the carpet. Any suggestions how to begin finding this short? thx
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post #2 of 8 (permalink) Old 11-08-2016, 09:28 AM
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I don't know how similar the circuit on a 67 convertible is to a 69 hardtop, but it's a strange one. On my 69 HT, power to the light comes from a connection to the rear harness in the vicinity of the drivers side rear wheel well. From there a wire goes to the door switches, which turn on the light by providing a path to ground. The two switches are NOT identical. One of them (at the end of the circuit) is a simple on/off that completes the path to ground when the door is opened, and breaks that connection when the door closes and the plunger is pushed in. This switch will have only one wire connected to it. The other switch has 2 wire connections, one comes 'from' the light socket, the other goes to the other switch. When the door is open/plunger out, it connects the input wire (from the socket) to ground and turns on the light. With door closed/plunger in, it connects to the other wire that goes to the other switch (so that when that door is open it also completes the circuit). If the wires aren't connected to the correct terminals on the "2-wire" side, or if the switches have been reversed (installed on the wrong doors) it can cause what you're seeing.

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post #3 of 8 (permalink) Old 11-08-2016, 10:59 AM Thread Starter
 
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Intersting indeed, however the door switches in my 67 are both single wire switches.
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post #4 of 8 (permalink) Old 11-08-2016, 11:04 AM
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What happens if you disconnect the wires from both switches and leave them disconnected?

*IF* (and this is a huge if) the circuit is similar to that on my 69, then disconnecting both wires should completely disable the light --- as that's how it gets to ground. If it still stays on (again if it works like my 69) with the wires disconnected, then check the light socket itself to see if it's somehow grounded - maybe remove it and leave it dangling.

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post #5 of 8 (permalink) Old 11-08-2016, 12:11 PM
 
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Originally Posted by pmrt View Post
OK, so I bought my beauty about a month ago. 21K original miles. However age is age and I am working through some issues. I fixed a rough engine (needed a new condenser). Slow convertible top (leak in a hydraulic hose, filled the resevoir) and now the interior lights. I noticed the night I brought the car home that the interior lights would come on when I hit the brakes. OK, a short I thought. I'll get to it. A couple days ago the fuse that powers the brake lights and interior lights burned out so I replaced it (20A) and surprise: the interior lights are now on permanently whether the brakes are applied or not.

This is what I have done so far: 1) taken both door switches out of the jams to remove them from the equation. No change. 2) disconnected the brake light switch under the dash. No change. I tried turning the interior light switch on and off several times to see if that would do anything. No change. Im at a loss as to the cause or even how to begin trying to find it. I read something about a ribbon cable short under the carpet. Any suggestions how to begin finding this short? thx
A short should blow the fuse. I had a similar problem in my '67 coupe. The dome light bulb housing clips had worked their way out of the plastic base and were grounding to the underside of the roof. I'd put a new fuse in, step on the brakes, and the fuse would blow since the dome light was on the same fuse. It seems to me that your problem is in the headlight light switch. I turn mine counterclockwise till I feel resistance, and then a little more and the interior lights come on. That's the source of power. So if you turn the knob fully clockwise and the lights are still on, then I'd say the headlight switch is bad. Though I've never had mine out, you could could try to pull the leads off to see if the lights go out. Photobucket is down again but once it's up I'll post photos of what the switch looks like or you could try Googling for images of it if you're in a hurry.
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post #6 of 8 (permalink) Old 11-08-2016, 02:47 PM
 
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Photobucket is up. If it goes down these photos disappear until it is back on line.



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post #7 of 8 (permalink) Old 02-16-2017, 05:52 AM
 
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You can bench test your light switch if you have it out I just replaced mine. I had my dome lights always on too. With your ohm meter test for continuity you get the bottom spade conector and the metal clip that's on the bottom of the switch and rotate the dimmer if it's always grounded it's bad if it opens once rotated it's not your switch. There is a YouTube video on that.
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post #8 of 8 (permalink) Old 02-16-2017, 04:49 PM
 
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Odd suggestion: Remove all the brake light bulbs and replace one at a time. It could be you have a bad bulb that is back feeding through the interior lights.

I've seen weirder...
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