I lost power to my cigar lighter, dome light and glove box light. The fuse is good. Can someone confirm that these are on the same circuit? Tough to tell on the wiring diagram. Thanks.

 

Yes, they are. It's fuse F7, the bottom left fuse in the fuse block. It's a 15 amp and powers the dome, cargo, courtesy, glove box and underhood light, vanity mirror and cigar lighter.
I'm assuming this is for the '78 in your signature.

 

Thanks! It is for the 78.

 

So, I traced the wires, double checked the fuse. I'm at my wits end. Any idea where this circuit grounds? I figure it's go to be a problem at the beginning or the end since the whole circuit is gone.

 

I doubt it's a ground. All three items ground in different locations. The dome has a short wire that screws to the roof substructure and the cigar lighter and glove box light ground through their contact with the metal dash. Even if the dash had a bad ground, the dome should still work.
You need to get a voltmeter and start checking voltage, first at both sides of the F7 fuse, then at each of the items that don't work. "If" it is a ground problem, which I don't think it is, it will show voltage.

 

could be a chassis ground, do you have a wire running from batt to inner fender or core support?

 

Can you describe in detail how you are checking the fuse? If the ground responsible for these circuits was in question, you'd be having a lot of other problems.

 

Thanks, I'm going to assume it isn't the ground for now and work the meter again. I'll update if I don't find power. One more quick question, Keyed power for the cigar lighter or is it always hot like the dome and courtesy lights? Thanks again!

 

Cigarette lighter is hot at all times.

 

Thanks. I assumed so, same circuit and all, but wanted to know for sure.

 

My fuses block is starting to go. pull it and check the back. mine is rusted. Already moved one
circuit to an axuilaiary block. I also have a short through the firewall.

on that circuit. shake the wires at the firewall!

 

I confirmed power to both sides of the fuse using my test light. I also confirmed the connection on the back of the fuse block is good. I do not have power at the dome light. I traced the wire through the pillar and out under the dash into the harness. I also traced it (Blue with red stripe) from the fuse box into the harness. It's only about 8 inches of wire in the harness. I can't understand what's going on in the harness, no connections and appears to be one solid wire all the way to the light, but no power. I know the door jamb switches and the light switch somehow are part of the circuit, but I can't see it.

For the cig lighter and the glove box light, I removed the glove box and traced both wires to a triple connection (green with yellow) There is no power to this connector, so the issue has to be upstream from it. It enters the harness and doesn't appear to exit until it gets to the fuse box also.

When I look at the wiring diagram it appears to run through the light switch (New) or the ignition switch, or both, but I can't really tell.

I'm open to (and very grateful for) any suggestion to continue my diagnosis! Thanks!

 

The dome light is a BLACK with BLUE stripe wire. Dash lights are BLUE with RED stripe. They are separate circuits, as follows:

Dome Light: GREEN with YELLOW stripe is the hot-at-all-times courtesy lamp circuit that comes from the fuse panel. It goes to both the door jamb switches as well as the headlight switch, either of which can trigger the dome light. Switched power to the dome light then leaves all three as a BLACK with BLUE stripe wire. You know the fuse is good; next you can check power going into all three switches (2 door jamb, plus the headlight switch) by checking for hot-at-all-times power at the GREEN with YELLOW stripe wire going into each of the three switches. If there is no power there, you know there is a break in the harness. If there is power there, the next things to check are the switches.

Dash Lights: BLUE with a RED stripe leaves the headlight switch and goes to the fuse panel to feed the instrument panel illumination fuse; the signal leaves the other side of the fuse again as a BLUE with RED stripe wire and is distributed throughout the dash. Since you haven't indicated you're having trouble with your dash lights, I've omitted any further explanation.

Your thinking is accurate.

No part of the lighting system runs through the ignition switch.

Based on your descriptions so far, it sounds like there is a break in the harness shortly after the load side of the courtesy lamp fuse. My only other suggestion would be to check the power at both sides of the fuse one more time, this time with the circuit loaded (glove box open, a door open, dome light switched on, etc). Sometimes fuses (especially glass fuses) can be close to the point of failure and act like a large resistor - with no current flowing through them, you'll see power on both sides; with current passing through them, the voltage collapses and there appears to be no power downstream of the fuse. This happened with my blower motor fuse and drove me nuts.

Nice work on your troubleshooting by the way; methodical and thoughtful steps are what get problems solved.

 

Outstanding! I found a better wiring diagram also and am excited to check the "hot in" at all three switches tomorrow. I ran out of sunshine today. Very grateful for your help! I'll post what I find out.

 

Okay, next step. The Black and Orange to the headlight switch is hot as is the yellow which I believe is the horn relay. I get nothing when I probe the green and yellow. I tried manipulating the switch, but still get nothing no matter where it is positioned, on or off. I have no power at either door jam switch. Is this a switch issue? I replaced this headlight switch less than a year ago and even bought the three times as expensive made in 'Merica version. I know anything can go bad though. The ceramic disc in the switch is very hot to the touch with the headlights on. Ideas?

Follow up, I pulled the headlight switch and checked for resistance with my multimeter across several spades. The horn relay spade to hot and I get the .3 I expect. The GREEN with YELLOW spade to the hot BLACK and ORANGE gives me infinite resistance. It might be time to throw a part at this thing.