1985 Fiero SE 4 cyl.

Courtesy lights dont come on (dome, floor, and trunk lights). Checked fuses and the fuse is blown. There are no circuit breakers installed for electric doors and mirrors because there are no power options on this car. Checked all connections for all switches and lights associated with this circuit with a Fluke. All seems to be in order, yet when I check for continuity between the hot side of the fuse it goes to ground. I suspect this is the root of the issue. Problem is I cant seem to find the short to ground. Also while looking for this short I found that the passenger side door switch only has one connection, the white wire (common return), cant seem to find the orange wire anywhere on it. Is this normal? So without having to complete tear my wiring harness completely apart, where does the hot wire on the fuse panel for the CTSY fuse go to? I figure it goes straight to the battery block but I am not sure.

Any thoughts and suggestions?

It's normal for the passenger side door switch to have only one wire, it controls only the courtesy lights whereas the driver's switch controls the courtesy lights and the ajar light. The switches don't have a ground wire, they ground through the body of the switch itself. As for determining where your short circuit is, in almost all cases it's a case of the connectors on the door or trunk lid that are bent a little and touching the surrounding metal door frame or trunk metal. Unscrew all of the switches and leave them dangling. Next use your mulitmeter on the demand side of the fuse recepticle to see which switch causes the circuit to go to ground as you replace the switches one by one. Once you've isolated which switch is causing the problem, have a good look at it and there's a good chance you'll see what's up.

If this doesn't work, then the most likely trouble is a wire that's chaffed through somewhere and touching bare metal. This is a lot harder to chase, but not impossible. Try the first test above and post back if you still can't find the short.

quote Originally posted by peterson74: ... when I check for continuity between the hot side of the fuse it goes to ground ...

Are you performing this continuity check with the battery connected? I hope not. If there is no +12 volts on the hot side of the fuses with the battery connected, then the wire between the battery and the fuse panel is open somewhere, most likely at the fusible link.

You are reading a low resistance to ground on the hot side of the fuse panel either 1) because there is actually a short to ground somewhere, or 2) because you are actually measuring the parallel resistances of all the devices downstream of the fuse panel, not a wiring fault. Step one is to isolate the fuse panel by removing all the fuses, and then troubleshoot from there.

Well I have yet to hear an attempt to just replace the fuse with the proper size and see if it blows. Has this been done?

LOL. I would have thought that would have been obvious. Yes it does blow every time, it even blows when I put a larger amperage in it. I will try the switch thing, I already have the two door switches dangling out of the holes, I guess I should have done the trunk too. This would be a whole lot easier if the schematics showed where the hot wire runs from before it gets to the fuse box. Yes i took the reading with no fuse in the holder and with the meter on the hot side and the frame I get low Ohms showing a short. I get the same when I remove the POS terminal from the battery.

Do you have a Haynes manual? The power goes from the fuse, to the trunk release, to the power locks/power mirrors (you don't have) and then to the lights. The other side of the lights then go to the switches which when the doors are open to ground. So if any of the switch wiring (WHITE) gets grounded the dome lights will come on.

HOWEVER it WILL NOT blow the fuse. There is no chance that where you are looking will blow the CTSY fuse. All it would do is turn on the dome lights

Phonedawgz is right... even if the wires at the switches were to ground out somewhere along the path, all it would do is turn the lights on, not blow the fuse. You have to find where the orange wire leading from the fuse panel to the various light bulbs (not the switches) is grounding out. A common place for this is in the overhead light console. Often when screwing the overhead console into place, the orange wire gets pinched between the housing and the frame, or one of the four screws pierces the insulation on the orange wire. The other most likely spot is in the trunk area where the orange wire and white wire pass through the trunk wall through a grommet. If the grommet fails, the wires chaff through and contact the sheet metal of the trunk wall.

I have all the lights and switches (except the trunk lid switch) disconnected so there is no chance of them causing the short. Either way I am not talking about that side of the fuse holder. I am talking about the side with the big red wire feeding in from the firewall. The one that I assume is going straight back to the battery or more likely a fuseable link. The other wires on the back of the fuse box, the BATT fuse included do not short to ground just the CTSY fuse. Oh and I meant no disrespect earlier. Swapping the fuse was the first thing I did. Got lots of time chasing wires in aircraft myself. Was just looking for ideas on where or what it could be if others have seen this before or not. I figure I will probably be chasing this back into the engine bay. Oh well time to get dirty.

Another idea I had was cut and splice the red wire from the BATT fuse connection to the CTSY connection its the same 12 volts I figure and will have its own fuse to keep the amps down. But Im worried it may draw too much on that wire and cause a fire. Probably better just to pull a new wire in from the battery block.

Thanks for the clarification. I was beginning to question what you meant when you referred to the "hot side" of the fuses. I think we're all on the same page.

[This message has been edited by Marvin McInnis (edited 09-08-2010).]

Anything that might be wrong with the red supply wire TO the fuseblock will NOT blow the fuse in the fuse block.

Replacing that wire won't solve anything.

Looking at Haynes - Power Distribution - the RED wire that feeds power to the CTSY splices with many other fuse supply RED wires at Splice S206. When you read continuity to ground when checking that side of the fuse you are just reading continuity to ground through the other circuits that are spliced into that power feed.

If the trouble you are looking to troubleshoot is the CTSY fuse blows - then the trouble HAS to be past the fuse, not before it. It has to be on the ORANGE wire leading away from the fuse box, or a wire that subsequently connects to the orange wire

[This message has been edited by phonedawgz (edited 09-08-2010).]

So that wire can read continuity to ground then? Not sure that sounds correct.

Look at Haynes - Power Distribution

That RED wire is spliced in with wires that lead to the fuel pump - the coolant fan - the key switch and everythign after that - the blower fan, and the AC. All those things work by connecting the power source, through the device and finally to ground. Yep you WILL read resistance to ground when checking that way.

Look at it this way. Hook up the battery again. With the fuse out you WILL have +12 on the supply side of the fuse. If so the supply side of the fuse wiring is OK. Again there is no way the supply side of the fuse wiring is going to blow the fuse. The fuse is blown because there is too much current being drawn through the fues - ie being drawn on the orange wire.

quote Originally posted by phonedawgz: The fuse is blown because there is too much current being drawn through the fues - ie being drawn on the orange wire.

This is absolutely correct. You cannot blow a fuse which is downstream of a short. The problem is on the orange circuit. If the problem were on power supply side of the fuse, you'd blow the fusible link.

[This message has been edited by Bloozberry (edited 09-08-2010).]

*SIGH*... alright back to the drawing board. time to get upside down and dirty again. They really didnt have guys like me in mind when they built these. Too bad I love them so much.

Pull apart C201 and see if the fuse still blows

C201? Im looking in the books and I dont see a reference to a C201. I imagine its a connector just not sure which it is.

C201 is a 6 cavity connector hiding under the dash near the instrument pod which has only four wires leading to it... to help identify it, one wire is orange, and one is purple on one side of the connector and tan/white on the other side. If you can find it, by disconnecting it you'll remove the effect of dome light circuit from the rest of the car. If you still get a short with C201 unplugged, then you know the short is on the segment of orange wire leading to either the trunk release switch (if you have one) or the trunk light. If you no longer have the short after disconnecting it, then the trouble is on the dome light circuitry.

Look under the drivers side kick panel up high towards the front of the car

I have the dome light housing completely disconnected and it was still doing it. I suspect then that it is the trunk this is the only place I have not disconnected the trunk lid ajar switch. The trunk light was completely removed the wires are hanging.

While I may not understand the original question of this thread, I didn't see anyone mention to you that your courtesy lights are hot on two different circiuts, when one fuse blows out, you get a back feed through the other circiut causing the symptoms you describe.

Scroll down a bit to read "The phantom courtesy light mystery".
http://www.fieros.de/en/articles/screwup.html

Hope this helps.

and see cave... sneak path in electrical general section.

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave (It's also at the top and bottom of every forum page...)

But that doesn't make the fuse blow, which is the OP actual problem.

** if the hot wire was somehow connected to ground before the fuse panel - the fuse will NOT blow - the wire would burn up between the battery and the short to ground.

The purpose of the fuse is to limit current flow through it, since it is blowing, the short is in the harness AFTER the fuse.

There's a fuseable link by the battery that would blow. A large number of other circuits would go dead if teh fuseable link were blown, plus you would not get +12v on the supply side of the fuse.

quote Originally posted by phonedawgz: There's a fuseable link by the battery that would blow. A large number of other circuits would go dead if teh fuseable link were blown, plus you would not get +12v on the supply side of the fuse.

I stand corrected, but the fact that is has not blown and it is the fuse that blow that indicates the main power feed is ok.

Agreed.

Well tested with the C201 connector off and looking for continuity to ground from the orange side of the fuse block. Still getting continuity. Looked at the schematic and it looks like the rest of it goes to the lighter, and radio. I have completely disconnected the trunk lid switch, and both door switches as well as the dimmer switch and I still get a short to ground on the orange side of the CTSY fuse only.
Either way my problems are far worse than the electrics now anyway. Car drove fine for a few weeks, but now it wont start. It turns over fine but does not fire off. If I play with the ignition switch some, i get it to back fire from the TBI. Eventually after about a half hour of this, it will start and run. If i turn it off and let it sit for a half hour, I am back to playing with the ignition again for a half hour. Not good for the starter I am sure. Took the distributor apart and noticed that the metal sufaces inside are quite rusted. So I suspect a bad distributor unit that is not throwing the right timing. In addition to this, I have a lot of oil leaking on the passenger side of the engine, but like someone else here, am finding it hard to find the source of the leak. For this I suspect the oil pan gasket and timing cover gasket. Looks like my cheap lemon is going to start costing me a fortune. Oh well still love this car no matter. Thanks again for everyones help.