[JBanna]

Hello all,

Today I started my car and burnt the fuse; after that I noticed my dome and floor light constantly stay on, but only half brightness; however, when I open either door or turn on the lights with the headlight switch, the three lights go to full brightness; my stereo has no power either, although it is not connected to that circuit. I removed both door jamb switches with no change, and a new fuse burned immediately. I hate these kind of problems! I do need to replace my alternator, but can't see how that could cause this, especially since it burned when I started the car...any other knowledge out there?

Thanks,

Joe

[Trevor78]

Check the headlight switch, especially if you have swapped out lighting.

[JBanna]

I replaced the headlight switch about a year ago, but I will eventually get to the headlight switch, after some other steps....if there are other ideas out there, any help would be welcome!

P.S. That fuse also covers the lighter and clock - I did find a broken spade on my floor mat right underneath the location of the clock, after I was moving some wires around (gently though), but the spade looked pristine, not 45 years old; however, does that sound related? I initially disregarded that as a coincidence considering a broken spade should simply render inoperable the component to which that spade belonged....I have not gotten close to the lighter yet, so a problem there seems unlikely.....by the way, I should be able to check continuity between the components and the fuse box, correct? Does it matter which side of the fuse location I choose? Also, if there is a short somewhere, would a continuity test even work? ....it seems like a short would always result in continuity in that circuit....am I correct?

[Greg Reid]

You have an 'unauthorized' ground somewhere. The ground that blows the fuse is also powering the dome lights. The button in the door normally operates the dome the same way, by providing a ground. It's coming on brighter when you open the door because it's a better ground.
Do you have an ohm meter? Check each side of the blowing fuse's holder to ground. If it's reading short you need to check everything that fuse normally controls and their wiring harnesses. Leave the meter hooked up and watch for the short to disappear.

[JBanna]

That sounds logical, but what should I see on the ohmmeter that indicated a short? No resistance? I'm not looking forward to checking the wiring!

[Greg Reid]

A short would be indicated by zero or low resistance to ground. If it's blowing fuses it's going to be fairly low.

["QUICK-SILVER"]

Is the stereo aftermarket with a memory wire?

The glowing dome light thing is normal when the tail light fuse is blown.

Problem will not be in the white ground wires that go to door jamb switches.

Memory power to an aftermarket stereo would be my first guess.

Clay

[JBanna]

For all out there, I found the problem - I focused on inspecting all the wires under the dash between the console and the parking brake - the last time I had my dash apart I lowered the steering column for better access; when I put it back together, I wasn't careful enough and managed to get the main instrument cluster wire loom between the steering wheel and it's upper mounting bracket. So, after several years, the insulation of the worst of the crushed wires (the orange and black courtesy light wire) wore through enough to cause the short and power the courtesy lights at reduced brightness. One thing I don't know is why the courtesy lights would still go to full brightness using either the headlight rheostat or opening a door, considering the fuse was blown/removed...

No easy diagnosis and a real pain in the ass to fix, but thanks for the replies!

Joe

[Greg Reid]

As I stated before, the courtesy lights work by being provided a ground. Your lights are staying on because of that pinched wire and through that wire, or through the steering column that is, they found a ground. The designed ground in the rheostat or the door buttons is a better ground so it was brighter.

[JBanna]

Thanks Greg, that makes sense; however, I spoke too soon - after careful reassembly I now do not have the kick panel lights. I've checked their wires and they seem ok, no fuses are burnt, and everything else works properly...any ideas there? I really hate these problems!

P.S. Do you know how the clock gets its power? I only see the tach plug next to it...

[Greg Reid]

I have to make a disclaimer here, without a schematic I'm just guessing.. My guess on the courtesy lights staying on is because I know that a ground is what they need to come on so they were getting a ground somewhere. Ground on a hot circuit will also blow a fuse so that's where I came up with my theory. The fact that your kick panel lights are not coming on now is, I'm guessing, probably from an open rather than a short. A disconnect.
You can do wonders with a schematic and a volt ohm meter. With the schematic you can trace the source voltage for your kick panel lights and with the meter you can find out where the voltage is being lost.
That schematic would also show you the clock voltage source btw.

[Greg Reid]

Is this the car in your signature? I still have a Firebird manual here that will have a basic block diagram type schematic '67-'81 models. Chilton's schematics don't have a lot of detail but will give you an idea of what wire to check.

[Greg Reid]

Here is the drawing for '78-'81. Hope it's readable. You can see that all of the lamps, both instrument panel and courtesy, are hot at all times and are turned on by connecting to a ground whenever one of the switch positions is toggled. The kick panel lamps I would assume are in parallel to the courtesy lamp. Use a meter or test lamp to probe the wires going to the kick panel lamps when the door is open. You're either not getting voltage or not getting a ground, one or the other. Assuming bulbs are good.
Edit- one more thing I noticed on this schematic. There is a black or tan wire coming from one of the door switches to the turn signal switch. I think you mentioned something about going into the steering column?


Sent from my moto g stylus (2021) using Tapatalk

[JBanna]

I did find the clock power source, which comes from the instrument cluster loom then to the printed circuit - I think my clock must have failed considering I replaced the printed circuit a few years ago, plus it never kept good time anyway, even back in '82 when I bought the car.

I'll do some more trouble shooting of the kick panel wires, but I know the door switches are controlled by a tan wire and the ground between the switch and the door frame as you screw them in - they work fine...but I wonder why the turn signal gets its power from the tan door switch wires? Figuring out these kinds of issues is a real head and back ache!

I found a crushed wire between the steering column and its mounting bracket - it was causing the short that started this whole nightmare. I guess I didn't position it correctly the last time I had my dash apart - to resolve that issue and prevent it from happening again, I rerouted the loom, which gave me a lot more room to work with upon reassembly - I wish the damn engineers who designed the mess would have thought of that - it only took me about 20 minutes to do it; anyway, I'm certain nothing in the area of the dash is now causing my kick panel lights issue...

[JBanna]

By the way, I finally decided my Haynes manual isn't thorough enough, so ordered the two volume service manual, which should arrive in a couple of days...

[Trevor78]

Sent a PM.

["QUICK-SILVER"]

Tan wire on drivers side door jamb switch is the ground for the key buzzer.

Clay

[JBanna]

That's good to know - my key buzzer does work...