Horn and backup lights fuse blowing

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83AC
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Location: Columbia River Gorge
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Horn and backup lights fuse blowing

Post by 83AC » Wed Mar 23, 2016 8:18 pm

Alright electrical and wiring gurus, the fuse to the horn and backup lights keeps blowing. I though maybe a ground or corroded wire issue. I pulled fuse panel, saw a ground not connected and reconnected it. When I restarted it blew right away. Looked at the back up light connections under the van at the transmission and they look fine.

How do I isolate one or the other? What should I be doing to troubleshoot from here? How do I trace the wires - is it going to be as much of a pain in the butt as it seems? Check inside the steering wheel to see if the horn is wired correctly?
Say what you mean; do what you say.
1983 AC Vanagon camper - Penny Lane

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Amskeptic
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Re: Horn and backup lights fuse blowing

Post by Amskeptic » Thu Mar 24, 2016 3:08 pm

83AC wrote:Alright electrical and wiring gurus, the fuse to the horn and backup lights keeps blowing. I though maybe a ground or corroded wire issue. I pulled fuse panel, saw a ground not connected and reconnected it. When I restarted it blew right away. Looked at the back up light connections under the van at the transmission and they look fine.

How do I isolate one or the other? What should I be doing to troubleshoot from here? How do I trace the wires - is it going to be as much of a pain in the butt as it seems? Check inside the steering wheel to see if the horn is wired correctly?
The horn button is on the ground side of the horn circuit, so it cannot blow fuses. All it can do is make the horn operate without your consent.

See if you can follow the positive horn wire that leads from the fuse box to the horn itself. Start at the horn and work backwards. Check for abrasion at body holes. Disconnect the wire at the horn and install a fuse. Does it blow? Problem is upstream or in the reverse lamp circuit.

Does fuse not blow? Plug in the horn. Does fuse blow? Horn is shorted internally.

The reverse light circuit is positive through the switch and back to the reverse lights.

I would unplug both wires at the reverse switch, install a new fuse. Does it blow? Short in supply wire to reverse switch. Does it not blow? With your tester, see which dangling wire has power.
Plug it in. Does fuse blow? See above. Does it not blow? Plug in other wire. Does fuse blow? Short in wiring to reverse bulbs or short in taillight housing/bulb socket.
Colin
BobD - 1978 Bus . . . . . . . . . . .111,130 miles
Chloe - 1970 bus . . . . . . . . . . . 206,787 miles
Naranja - 1977 Westfalia . . . . . 94,615 miles
Pluck - 1973 Squareback . . . . . 55,510 miles
Alexus - 1991 Lexus LS400 . . . 72,990 miles

83AC
Getting Hooked!
Location: Columbia River Gorge
Status: Offline

Re: Horn and backup lights fuse blowing

Post by 83AC » Thu Mar 24, 2016 8:30 pm

First I checked the horn and traced the positive wire - it looks good. I unplugged both wires at the. Horn and put in a fuse - it blew. Leaving them unplugged, I unplugged both wires at the reverse light switch. Put in a fuse - it blew. So that stinks. It was dark and now using my flashlight I took down the fuse panel, tried to get a look and couldn't see much between the shadows and mess of wires.

So, this confirms the problem is somewhere "upstream," correct? Would a logical next step be to try disconnecting the wire to the horn at the fuse and trying a new fuse? Then if it blows = problem with reverse light wires. If it doesn't = problem with reverse light wires. Am I on the right track here?
Anderson
Say what you mean; do what you say.
1983 AC Vanagon camper - Penny Lane

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Amskeptic
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Re: Horn and backup lights fuse blowing

Post by Amskeptic » Fri Mar 25, 2016 6:29 am

83AC wrote: So, this confirms the problem is somewhere "upstream," correct? Would a logical next step be to try disconnecting the wire to the horn at the fuse and trying a new fuse? Then if it blows = problem with reverse light wires. If it doesn't = problem with reverse light wires. Am I on the right track here?
Anderson
Yep. We'll be waiting for your next installment. :happy1:

It like totally . . . blows, this fuse blowing stuff. If you don't like going through fuses, you could try a test light to ground or even a little circuit breaker between the fuse terminals.
Colin
BobD - 1978 Bus . . . . . . . . . . .111,130 miles
Chloe - 1970 bus . . . . . . . . . . . 206,787 miles
Naranja - 1977 Westfalia . . . . . 94,615 miles
Pluck - 1973 Squareback . . . . . 55,510 miles
Alexus - 1991 Lexus LS400 . . . 72,990 miles

83AC
Getting Hooked!
Location: Columbia River Gorge
Status: Offline

Re: Horn and backup lights fuse blowing

Post by 83AC » Sat Mar 26, 2016 1:03 pm

Alright! This problem is solved! I decided I'd check the wire for the reverse lights first; pulled it, checked for power to the fuse before putting in a new one - has voltage. Put in new fuse - doesn't blow! Tried horn - beep beep loud and proud! Big smile! Followed the wire for the reverse lights to the bundle, and it looks great. Only interesting thing is a clipped in wire that disappeared into the dash. I gave it a trace and tug and it isn't connected to anything! Just clipped off leads! WTH? No tape on end. It's part of two wires and the other is clipped to a different wire. Anyway, I pulled those out in the open, hooked the reverse light wires back to the fuse, started her up and the fuse doesn't blow! In reverse, lights are on! Horn - beep! Beep! So, I think that wire was grounding out on something under the dash. Taping off the wire to stop problem and keep things good!

Thanks, Colin for the guidance! It feels so good! Woohoo! Now, back to the engine . . .
Say what you mean; do what you say.
1983 AC Vanagon camper - Penny Lane

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