GKO777

Thanks for all the replies so far.
Lionel, I also ruled out the headlight switch. My next plan was to rule out the green wire going from headlight switch to fuse box by removing the small dash light fuse.
When I did that, I didn't get power anymore at the right side of the courtesy light switch when I tuned the lights on, so the probem must indeed be between AFTER the fuse box, and somewehre in the dash harness (grey wire touching orange/white wire).

But I may have more problems...
In the video's below I checked continuity accross fuses. When you hear the beep I have a closed circuit.

Strange thing is that I have continuity for the dash light switch fuse, with the fuse removed?


Not good to see here, but one end of mulltimeter is in the right connection of the courtesy fuse (with fuse removed), and I'm checking continuity accoss fuses.


Could this be a fuse box issue? Any other ideas?

lvmyvt76

you have a back feed from somewhere.

lionelhutz

I wouldn't worry about that too much. Both sides are likely grounding through the various bulb filaments. One side is grounded via the various interior/cluster lights and the other side is grounded via the various running lights.

henrikse

You can't use a continuity checker without isolating the circuit. There are too many runarounds .

henrikse

I would forget about turning the headlamp switch on or to the left. Remove the coupler even and try to get your courtesy lights working. Whatever is wrong with them could quite well be the problem. If you have multiple problems you have to work on one circuit at a time.

GKO777

Ok, after reading all replies, I'm thinking of removing the dash completely, opening the wiring harness and isolating the courtesy light wiring (white/orange) from the rest of the harness.
Is that the correct course of action, or what would you do in this situation?

henrikse

Good idea. With the dash off you can fix a lot of gremlins I am sure you will find. It will make it a lot easier to see

GKO777

This weekend, I pulled the steering column (with a little help from my little friend )





Sounded straightforward, but I had some trouble getting the steering wheel shaft out of the rag joint end which took me way too much time.

Today I pulled the dash out.





The good news is I didn't break anything. But I still have to find the short and get everything back together again . A lot of work for some little lights (and a clock).

Enough for this weekend. Going to watch Fantomworks now and look at other people working

SwampeastMike

You have a cross circuit somewhere between the (dimming) dash lamps and the non-dimming courtesy lamps.

The white wire is the ground for the courtesy lamps. The lamps always have +12V (with the fuse installed). The door switches provide ground to the circuit just as does the headlamp switch when you rotate the **** fully left.

+12V power for the courtesy lights is from orange wires. Any orange wire in the cabin is supposed to have +12V at all times (providing the ACC fuse is installed).

The dark green wire feeds the INST LP fuse with positive voltage (variable through the rheostat in the headlamp switch) from the headlamp circuit when the headlamp switch is pulled out.

The wiring on the other side of the INST LP fuse that feeds all of the dimming panel lights is grey.

Some things to try:

1) Remove all of the courtesy lamps. Don't forget the one of the spare tire if it's in your year. You want to remove ALL lamps that come on with the door switches. Remove both the ACC and INST LP fuses. Turn on your headlights and check for voltage at the fuses. You should have +12V on only one side of the ACC and variable positive voltage (check that it varies properly by rotating the headlamp switch) on only one side of the INST LP fuse. If you get variable power on both sides of either fuse you have a short between the green wire and an orange and/or grey wire. Hint: the dark green runs direct from the headlamp switch to the fuse box so there's not much opportunity for this to happen.

2) With lamps and fuses still removed, turn on the headlamp switch and check for power on the white wires at a door switch. They should all be dead. Reinstall the INST LP fuse. The white wires should still be dead; if variable power is present you have a short between the grey and white wires somewhere. Next check for power on the "other" side of the ACC fuse. If variable power is present you have a short between the grey and orange wires somewhere.

I'm suspecting you'll find the last thing to be the culprit--a short or cross between the grey (variable positive voltage for IP lights) and orange (unswitched e.g. constant +12V). Why? Those wires run throughout the cabin harness and any insulation damage due to overheating, age, rodents, etc. has a good chance of crossing them. Also those circuits (particularly the ACC) are the most commonly "messed with" with adding electrical accessories or replacing factory components. If you have an aftermarket radio, look there FIRST! Nearly all radios since the 80s require a constant source of power (the orange ACC wire) for station memory. It's also rather rare for them to use the factory standard IP lamp power to light the dial as their illumination tends to be non-dimming. A poor radio installer can very easily screw up the electrical system!

Wg72C3

Good luck GK0777, you have your hands full with this issue. As long as your little friend keeps helping you in the garage, I think its all good. Isn't this one of the best parts of the hobby?

GKO777

Ok, so I removed the center console so the dash harness is exposed.

Next I started to remove the courtesy light harness from the right to the left (so basically removing all the related white and orange wiring).

I found a splice with 6 orange wires:
1 hot wire from fusebox
2 to left courtesy light
3 to right courtesy light
4 to lighter
5 to clock
6 to rear harness connector (for rear compartment light)


I cut this splice to find that if I turn on the lights (with the courtesy light fuse still removed), there is power coming ONLY from the left courtesy light wire So the good news is it's not in the fusebox.

The left courtesy light is hanging loose, so the power is on the ground wire. Followed that one to a splice with all ground wires.

The only possible option was the ground wire going to... the headlight switch

So I removed the white ground wire from the headlight switch (again) and measured on the spade with the lights on, and yes, there is power on that spade that is supposed to only provide ground (my connection was not great, but voltage goes to about 6V)...


But when I disconnected the wire from the switch before (see earlier in this post), there was power on the disconnected white wire. This was the reason I ruled out the headlight switch then So something is different now. Could it be possible that the headlight switch somehow powers the complete ground circuit when it's turned on? That could explain why the disconnected white wire was powered before (because the swith itself was grounded when installed).

Do you think I need a new switch, or can this be repaired?

SwampeastMike

The only reason ground exists in the headlamp switch is for the courtesy lights. The headlamps, marker lamps, tail lamps, and instrument panel lamps all have permanent chassis ground with the switch providing only +12V or variable positive in the case of the instrument panel. I do though believe it possible for the headlamp switch to develop a problem such that "leakage current" goes to the switch frame ground which causes havoc in the courtesy circuit to certainly include that powered white wire.

I have a new (well, 3 year-old) headlamp switch in my '79 because the rheostat in the original had fried. I now have a battery run-down situation that points to the exact problem you're having with the headlamp switch [seemingly] the only place the problem can lie.

lionelhutz

Overall, what you are describing doesn't make much sense. This was your previous description.


If the courtesy lights fuse is removed, then in theory the orange wire side of the courtesy circuit isn't connected to anything else. The wires just float. You're now saying you have confirmed this and the orange wires don't get any power with the lights on and aren't connected to anything else but the bulbs. This means there would be no way for the courtesy lights to light when the headlights were put on. Even IF the headlight switch applies 6V to the ground circuit of the courtesy lights they can't light if the orange isn't connected. Even if the headlight switch put 6V onto the whole ground under the dash there is still no connection on the orange wires to provide a complete path for current to make them light.


As for the instrument panel light fuse blowing. This means that fuse is being overloaded. The fuse is after the headlight switch. The headlight switch provides power to the dark green wire. The dark green wire runs to the fuse block where it goes through the instrument light fuse and then on to the grey wires that power all the instrument lights. So, if the instrument light fuse blows it means there is excessive load on the grey wires which doesn't involve the headlight switch.

GKO777

It looks like the lighter wire was the guilty one.

At one point I had only 2 wires still connected on the courtesy light circuit: 1 to the fuse box and 1 to the lighter. All other wires were exposed and disconnected. And I still had power on the circuit when turning on the headlights. Since the lighter had never been connected I assumed it had to be an issue in the fuse box. So I was very glad to find that was not the case. Cut the lighter wire and the power went away.

So with that wire disconnected, I re-installed the fuse for the courtesy light circuit, and voila, let there be light!




I don't use the lighter, so it's tempting to leave it alone now. But I'll probably try to get to the source of the problem on that wire.

Sorry for the confusion sometimes. I think some of my tests were off, and I sometimes got incorrect results (probably due to a bad ground I used when handling the multimeter).

Now the next thing is getting everything back together without breaking something else...

Thanks for all the great replies, really means a lot when you're stuck!

SwampeastMike

So glad you seem to have found the source of the problem! Given the problems you've described--especially the presumed interconnection between the variable voltage INST circuit and the ACC circuit I wouldn't claim complete success too soon

Big2Bird

You have it all apart. Trace out the lighter. Keep going. Fix it all, and don't forget to change out all the lamps while apart.

DUB

NOT meaning to be a 'kill-joy'....but I have to agree.

Please take the time to read this so hopefully I can describe something that you may or may not already know.

The 12 volt source that goes to your CLK LTR CTSY FUSE comes in from the right side....and goes through the fuse and ends up in the center of your fuse panel where you have a terminal that you can plug something into to run it.

So knowing that the ORANGE wire gets 12 volts...anything attached to this circuit can not provide power or take it voltage away from the fuse.

BUT what can happen is a dirty terminal that holds the fuse can cause voltage to drop when more current is needed to power up a component.

So this is why I seriously doubt the cigarette lighter is the culprit.

IF the orange wire anywhere in the system gets grounded...and IF the wiring is correct....it would blow the fuse.

The white wire is only used as the 'control' to make the bulb get a ground and burn. So IF the bulbs were in the socket sna oyu were checking the white wire...it is likely you got voltage to some degree THROUGH the filament in the bulbs. This is why it is wise to remove bulbs when testing a circuit like this.

And YES...if the white wire has power on it and you turn the headlight switch **** or open the door...then the ground from either of these sources is going to go to the filament in the bulb and make it burn....because the filament is the one area in this circuit that is design to have a controlled short circuit....which is what a light bulb basically is. A controlled short circuit.

DUB