Electrical frustration..., This is starting to piss me off. Options

[BMartin914]

So I have a recurring electrical problem in which my front marker lights, rear marker lights and rear tail light do not work.

I have traced down the wiring, see no problems. Cut open the harness and inspected as much as I can see (which is most of it) and still see NO problems (melting, arcing, etc.). Tonight I cleaned ALL the grounds (under relay tray, trans strap, fuse box, etc.). I then pulled all of the affected bulbs and planned to put them back in 1 by 1 until the fuse blew. Didn't get that far. As soon as I pulled the switch out the fuse blew.

This leads me to believe that wires are arcing somewhere, but as indicated, I see no visible melting or arcing. Does anyone have any ideas? I am at the point where I am willing to re-wire the circuit to fix the problem.

Anyone have any ideas before I re-wire this b**ch?

Thanks.

[Series9]

The only thing that the front markers and the rear markers share in common is the switch. I would look under the dash to see if somthing is shorting across terminals on the switch and then check the switch itself.

[Series9]

Oh, what fuse blew. The markers are not all on the same fuse.

[BMartin914]

5th fuse from the left of the panel.

I believe its for just the left side markers and rear tail.

[Series9]

But the problem happens on the right as well?

Actually, these circuits share the flasher switch in common as well.

[BMartin914]

NO. ONLY the left side markers (f & r) and the rear tail light. I've got lights on the right side as well as turn signals all around.

[McMark]

I agree with checking the connections on the switch. Take down the fuse panel (2 phillips screws), unscrew the pull knob, unscrew the trim ring and it's freeeeeeee.

[Spoke]

Does the left side front parking lamp (the other filament with the turn signal) come on? It should be on the same circuit as the side marker lamps. On the 5th fuse, there should be 2 wires on one side of the fuse. One goes to the front markers and one goes to the back markers. The wire on the other side of the fuse goes to the light switch. With the light switch on, measure the voltage of this fuse to ground. You should see 12V on both sides of the fuse.

If you don't see 12V at the fuse, then check the wiring and voltage back at the light switch.

If you do see 12V at the fuse, check the condition of the lugs and push-on connectors for rusting or oxidation.

Since both front and rear don't work, the problem is the common wiring from the fuse box to the switch.

If you pull the switch out, disconnect the battery first. The schematics in my shop manual show a direct connection from the battery to the light switch without any fusing or fusable links. It could get ugly if this wire were shorted to ground.

Do you have a schematic for the vehicle? I've found this to be extremely useful when chasing electrical gremlins.

Good luck,
Spoke


BTW, the problem you're having is an open circuit. A short circuit would cause fuses to blow or lamps to stay on all the time. With an open circuit, stuff doesn't turn on although an open circuit may have been caused by a short circuit which fried wires but this is usually very obvious by the burned wires and smell.

[BMartin914]

Fuse panel is down (probably for the 5th or 6th time, as are the light and hazard switches). Only my turn signal works, the marker filament does not. I have successfully traced the wiring from the panel to the switch and do not see anything abnormal. I have also traced the two wires leading from the other side of the fuse. The wire that runs fore appears to be fine, but I can only see so much in the trunk area due to the wrapping. Same goes for the wire running back, wthout pulling the carpet up and everything out of the interior I cannot visually inspect the wiring completely. I have not put a tester to the fuse. With a fuse in and the switch on, the 5th fuse from the left blows immediately even with all of the affected bulbs removed.

I have put sandpaper the the connectors and grounds so there should be no rust/oxidation/corrosion there.

I do have a schematic (it's a '75), I will check the wiring to the switch to ensure everything is properly connected. All the lights functioned when I got the car, I hadn't done anything when this started to happen. I just noticed that I had no tail lights, then saw no markers, changed the fuse and it blew. Have probably gone through 3-4 boxes of fuses since then troubleshooting.

[Spoke]

Sorry I didn't realize that you had a short that was blowing fuses.

The 2 wires on the 5th fuse go to the front and back markers respectively. With the battery disconnected, try removing one wire at a time and measure the resistance from the wire to ground. With the bulbs installed, it should read about 3-15 ohms. If you show a dead short (0 ohms), then there's a wiring short on that leg. My guess is that it's one wire, either in the front or the rear.
If you're not sure which wire is the front or the back, remove all bulbs on the front or the back to see which wire shows the change in resistance.

Also try removing the all bulbs from the front and the back and measuring the resistance to ground. With all bulbs removed from both wires should read infinite resistance or no deflection of the meter. If you get a low resistance measurement, it means that you have a wire short somewhere on that leg.

Again, I think it would be only one wire, either in the front or the back. and I would guess it may be near one of the bulb holders. Once you've located the wire (either front or back), connect the ohm meter so you don't have to hold it and try jiggling the wire at one connector at a time to see if you can find a place where the short is by watching to see if the needle moves when you disturb the area. The short is somewhere, so be patient and check things one at a time.

Spoke

[ClayPerrine]

Check the front turn signal/marker light bucket. I would bet that you have crossed the ground with the turn signal connetions. The tab for the ground is connected to the housing, and if you mix it up with the power feed, you will blow the fuse. Same goes for the rear, but it's probably the front.

Drop the fuse panel, and look for the 2 wires on the 5th fuse from the left. IIRC, the wire colors are grey with a black tracer. Disconnect both and see if the fuse blows. then hook up one and see if it blows. If it doesn't, look to see which light is on, front or rear. Now unhook it and hook up the other one. NOw see if it blows the fuse. If it does, look at the one that was not lit up a minute ago. It has the short. Check with a ohm meter to see if that wire has 0 ohms to ground. Then disconnect the wires at the light and check again.

You should be able to track it down that way.

Or you could just disconnect the front light wiring and see if it blows the fuse... (IMG:style_emoticons/default/laugh.gif)

[BMartin914]

(IMG:style_emoticons/default/icon_bump.gif)

Still looking for any suggestions you guys might have.

There's gotta be more people out there with some experience with electrical problems -- come on, these cars are at least 28 years old, and that's the newest one!

I have very little experience with 30 year old electrical systems. Elbows from a**holes so to speak.

[Spoke]

Have you isolated the short circuit to the front or rear wiring?
Find out which wire is shorted and then you can put the other wire
back on since it should be ok.
Chances are there's only one short somewhere near a light socket.
Remove all bulbs and check the resistance to ground. Let me know
what you find.

Remember to disconnect the battery when moving
the fuse box or wires around it. The 914 must have been manufactured
before fusable links were invented. Any shorts on direct wires to
the battery while working on the fuse box and you'll be welding (until the
wire pretends its a fusable link and melts).

OK, one dumb question: did you have any work done on the lamps or
changed any lamps before this happened? How about any work done
on the car on or near the wiring?

Spoke

[BMartin914]

Trying to get as much input as possible before I get back at it once I get home.

No work done prior to the problem appearing. Everything worked when I got the car. I just happened to notice about a month later that I had no left rear tail light, then noticed no marker lights.

One other thing...the left rear light does or does not work in unison with the marker lights? I cannot remember what the schematic says. I am starting to think I may have two unrelated, possibly related problems, marker lights being the first, the left rear tail being the other.

[BMartin914]

Thanks Spoke...you were right.

Once I isolate the problem to the rear, I found a loose connection at the terminal. Snip, crimp, problem solved. Boy do I feel like a dolt.

Thanks for all the input guys. Another 914 problem solved with the help of this board. SWEET!

[Spoke]

Excellent news. I know how frustrating electrical problems can be. My buddy has a 68 Camaro and I've had to chase down some funky wiring issues for him. It's kinda fun for me. It also helps that I'm an EE and I also do tech support at work, most of it with folks not in the USA, whose primary language is not English, and all of it by email. Do me a favor and go burn some rubber tonight. I'd like to do the same but my 1.7L doesn't have the poop to spin the wheels unless its on gravel.

Spoke

[BMartin914]

So I get it back together, everything buttoned up and go to check for functionality. Alright! Lights at all 4 corners and signals, but the left ones are now brighter than the right. I figure I have the wires crossed so i switch them (w/out the tire off) and lose my signal. I'm hungry, so I'm calling it a night.

Back at it in the morning. Any suggestions? I am going to pull the wheel off tomorrow and get the diagram out to double check everything.