My guess is bad door switch. The interior lights don't go off when you shut the doors. I've opened the doors and manually pushed the switches just in case the door wasn't lined up well enough to engage the switch. I'm planning on going to the parts store tomorrow and picking up a couple switches. Are they as easy to swap as they look?

I don't think they could fail that way, typically when they fail the lights won't come on. When you open the door the switch closes and grounds the lights, not likely its somehow stuck grounded.

Check your dash dimmer switch, I accidentally rotated mine all the way up and thought something was wrong when my interior lights stayed on back when I first got the car.

quote Originally posted by Xanth: I don't think they could fail that way, typically when they fail the lights won't come on. When you open the door the switch closes and grounds the lights, not likely its somehow stuck grounded.

Actually getting stuck on is a common failure mode. The lights have power applied at all times, if any wire downstream of the light is grounded they will get stuck on. Those pin switches are very prone to failure, I have a flakey one on my passenger side door and the light comes on all by itself sometimes. The fix is to replace the door pin switches.

quote Originally posted by Xanth: Check your dash dimmer switch, I accidentally rotated mine all the way up and thought something was wrong when my interior lights stayed on back when I first got the car.

haha!! happened to me when I took my car out of storage :P I had totally forgetten about it at the time

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1986 GT Fiero Owner & Enthusiast
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Checked the dimmer switch, in fact I got in the car shut the doors and worked the headlight/dimmer switch's dimmer wheel all the way back and forth without so much as a flicker with the headlight switch in the on and off positions. Thought if there was a short or something in that switch I would get some sort of reaction during the process. If the door switches don't fix the problem I'll pull the headlight/dimmer switch out of my currently non-running GT and put it in the 84 and see if that fixes the issue. Thanks for all the helpful advice so far. You just gotta love this forum so many knowledgeable Fiero enthusiasts. With all of your help you just might make a shade tree mechanic out of a web developer / computer tech...heh.

The lights will also stay on all the time if there is a short in the trunk light, trunk release, power door lock or power mirror circuit. If that’s the case, the lights go out when you manually turn the dome light on.

So, I bought the door jamb switches. I replaced the one on the driver's side hooked up the battery, no change. I got to the passenger side pulled out the old switch and noticed a difference immediately. Only one wire on the switch. Is that the way it's supposed to be or am I missing the other wire? The switch has two posts for wires but only one wire attached to the switch. I've pulled back the carpet and can find no loose wire in there. If anyone knows the answer it would be GREATLY appreciated. I'm tired of hooking up the battery to drive the car and then unhooking it everytime it's going to be parked for more than a couple hours.

The second wire in the drivers switch is for the key alarm. You are only concerned with the white wire. There is only the white one in the passanger door.

[This message has been edited by Electrathon (edited 09-01-2008).]

That's what I was actually afraid of, that means I must continue diagnosing the problem. I am going to pull the headlight / dimmer switch out of my GT and put it in and see if that solves the problem, otherwise I guess I'll start sorting through some of the other suggestions that were made earlier in the thread. Oh, and plus to you Electrathon for your quick and helpful reply!

Thanks for the +, I gave you one too.

What you are looking for, assuming that it is not a switch, is the white wire is pinched to ground. The system turns on when it recieves a ground, that is why it only takes one wire. If something was done in the care reciently, start in that area.

Haven't found the problem yet, I'm starting to think I'm going to have to rip the dash out, heh. I'm determined though, I WILL fix it.

If you want to drive it over here I would fix it for you... Likely not worth the trip.

Try pulling out the overhead light assembly.

quote Originally posted by Electrathon: If you want to drive it over here I would fix it for you... Likely not worth the trip. Try pulling out the overhead light assembly.

I love a road trip as much as the next guy, but that's a BIT far... heh. Thanks for the offer though.

Having the same problem myself, now.

When I bought my early '84 2M4 a few months back, one of the things I noticed is that the courtesy lights, dome lights, and trunk light didn't work. Hoped it might be a fuse, but when I started looking into it, I realised that none of the bulb holders had any bulbs in. (actually, when I bought it, I found that a lot of the electrics didn't work properly - the wiring really got chopped up when the previous owner converted it to right-hand drive ).

It soon became obvious that the reason was that ALL of the bulb holders were always live and, if I have understood the preceeding posts, there is, somewhere, white wire unintentionally grounding the circuit.

Any places more likely than others, and is there any significance to the fact that the Door Ajar light doesn't work at all?

Looking at the wiring diagram, the courtesy lights are on a different circuit to the dome lights - the common point seems to be the light switch (I have already checked that the reostatic switch wasn't turned to the end, but haven't yet taken the switch out to visually inspect it).

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'85 SE 2M6 automatic (Left-hand drive)
'84 SE 2M4 manual (Right-hand drive)
'98 Ford Mondeo Si
'73 Peugeot 304 S Cabriolet

[This message has been edited by Madscanner (edited 05-30-2009).]

My '85 did that and it drove me bananas. Every one told me my fix wasn't a "fix" but it worked. I took out one of the map light lenses and loosed , just a little, one of the mounting screws that hold the map/dome light housing on. They're still working fine, go figure.

That seems to suggest that one of the ground wires is getting pinched by the interior light module...

I agree.

quote Originally posted by Madscanner: That seems to suggest that one of the ground wires is getting pinched by the interior light module...

Thus grounding the ground wire?

Power has to go through the switches to get to ground. The switch has to be defective or the power wire ahead of the switch has got to be grounded.

QUOTE]Originally posted by sanderson:Power has to go through the switches to get to ground. The switch has to be defective or the power wire ahead of the switch has got to be grounded.[/QUOTE]

To which switch do you refer?

[This message has been edited by Madscanner (edited 06-01-2009).]

quote Originally posted by sanderson: Thus grounding the ground wire? Power has to go through the switches to get to ground. The switch has to be defective or the power wire ahead of the switch has got to be grounded.

Yes. Grounding the dome lights white wire possibly by breaching the insulation with the screw or because the housing pinched the white wire enough to break the insulation and have it contact the metal header.

quote Originally posted by Madscanner: QUOTE]Originally posted by sanderson:Power has to go through the switches to get to ground. The switch has to be defective or the power wire ahead of the switch has got to be grounded.

To which switch do you refer?

[/QUOTE]

The switches in the dome light assembly. Theory being that switch was closed when it shouldn't have been but loosening the screw caused the switch to open.

[This message has been edited by sanderson (edited 06-01-2009).]