Fuses #1 & #2 blowing in 1970 bus

kolbek · Posted: Sat Sep 25, 2010 4:24 pm Post subject: Fuses #1 & #2 blowing in 1970 bus

Hi!

I am having a problem of fuses #1 and #2 (for tail, parking, and side marker lights) blowing in my 1970 bus any time I pull the light switch to the first stop.

If only one of the fuses was blowing, I'd start poking around to find a short between the fuse box and one of the lights. But, with both fuses blowing, I wonder if that means that there is some problem between the switch and the fuses? I also had wondered if there might be a problem with the switch itself.

How best to diagnose this without burning through a mountain of fuses or wasting time looking at more wire than I need to?

Thanks for any assistance!

busdaddy · Posted: Sat Sep 25, 2010 4:43 pm Post subject:

Welcome, a switch wouldn't cause that if it's wired like it was from VW, the fuses are down stream.
I'd suspect some mixed up wires on the tail light or front signal light fixtures, if it's been in the body shop it's not uncommon for someone to connect a grey or grey/red wire to ground instead of the brown. Also look at the rear marker lights, if they are aftermarket they are notorious for internal shorts.
Disconnect all the lights and start reconnecting them until you find the culprit.
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kolbek · Posted: Sat Sep 25, 2010 4:46 pm Post subject:

Thanks! So, it's not surprising for two fuses to blow if there's only one short?

Is my best bet to get myself a bucket of fuses and keep trying connections until they stop blowing?

Randy in Maine · Posted: Sat Sep 25, 2010 4:52 pm Post subject:

Do this...

Get yourself a 2' long piece of 12 gauge wire and put an alligator clip on each end. In the middle, solder in a 2 prong turnsignal flasher. That will give you a short amount of time to troubleshoot the bad circuit when you use the flasher as a temporary fuse.

Do as suggested above though and remove all of the bulbs at the sockets and inspect each one first.

busdaddy · Posted: Sat Sep 25, 2010 6:57 pm Post subject:

kolbek · Posted: Sat Sep 25, 2010 7:06 pm Post subject:

Yeah ive got the bentley so i've checking the diagram. I just found that I can complete a circuit between the two wires running to the back that are supposed to be on separate fuses. I'm not sure if I phrased that very well. When I hook up the gray/red in the front, both taillights come on, which surely isn't supposed to happen. That helps explain why both fuses are blowing. I still have no idea where the heck they're connecting...

I think the short is in one of the side markers. I'm still working through that.

Thanks for the help and tips!

Kolbe

kolbek · Posted: Sat Sep 25, 2010 7:12 pm Post subject:

Oh... That'll do it (crossing the two circuits, that is)! http://db.tt/FxEFPev

SGKent · Posted: Sat Sep 25, 2010 7:20 pm Post subject:

pull all the bulbs then see if it still does it. Need to know if it is in the bus or lights. You may be dealing with someone who stuck the wrong bulb in.
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kolbek · Posted: Sat Sep 25, 2010 10:05 pm Post subject:

Yay, I got everything working again! ... for now.

I think the problem was in the right front light. The bulb was very corroded and pretty well affixed to the socket. A little WD-40 got it out and cleaned things up, but I was still having problems with both filaments illuminating and with the fuse blowing, so I washed the socket with soap & water. I got everything put back together and the fuse seems to be holding now.

I still need to clean up the sockets for the side markers. They are just filthy and there was even some moss-looking crap growing in one of them Sad

... I just need to figure out how to get the bolts out of the side. The screw heads are stripping when I try to turn them.

Some fool had (very poorly!) spliced the gray/red wire with the gray/black wire in the engine compartment. I can't imagine why on earth someone would've done that; I just untangled the mess, put some butt connectors where they needed to be, and everything that needed juice got it. This same genius had put 16 amp fuses in for these circuits...

It seems odd that there is one fuse for the rear right, license plate, and front lights (5 bulbs, 7 filaments) and a second fuse just for the rear left lights (2 bulbs, 3 filaments). I wonder what the engineering rationale behind that might be.

Randy, I didn't have the materials to build the temporary fuse you were talking about. The parts store I went to happened to have a bunch of old 8 amp fuses lying around for really cheap so I bought a bunch of them and only ended up going through 5 more of them after I got home.

Merlin, your suggestion to pull all the bulbs is a good one. I need to go through and make sure other fixtures are not as degraded as the one that I think was causing the short. I only have more misery to look forward to if they are and I ignore them.

Anyway, I have lights again! Many thanks to all of you for the help.

SGKent · Posted: Sat Sep 25, 2010 10:27 pm Post subject:

kolbek · Posted: Sat Sep 25, 2010 10:31 pm Post subject:

Yeah I guess I was wondering why one of the front lights wasn't on that fuse, too. That'd be a really short wire run. Oh well, not something I'm going to spend too much time worrying about Smile


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