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Old 12/07/07, 07:49 PM   #1
JaxLax
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Bad Relay (blowing fuses)

I'm at my wits end and I ran out of fuses so I had to give up

I have a set of two relays for my headlights, one for high and one for lo beam. They are wired identically. They are grounded identically. Yet one blows the fuse everytime.

They worked great for about 8 months and it just started last week.

1) saw it was blown
2) replaced it, blew the second the switch was flipped.
3) swapped the triggers (hi/lo beam), blew the fuse on the other trigger
4) rechecked the ground (cleaned and tightened), blew
5) swapped grounds (hi that was working for the lo that wasn't), blew the fuse


Basically, I don't know what the problem is. Could the relay have gone bad? That was my next trial, but i'm out of fuses so it will have to wait til tomorrow...
gonna buy at least 10 (hey i need @ least 3 to fill in and 3 to back those up so i got 4 to blow (horrible pun))

Red 77: SOLD
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Old 12/07/07, 09:17 PM   #2
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Run a check on the wires. Look them over good and make sure a power wire is not grounding out somewhere. Could have a chafed wire. A power wire grounding out on the body would cause a fuse to blow instantly.

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Old 12/07/07, 11:13 PM   #3
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It sounds as if it could be the relay . When they go bad the lights normally will just not come on though . It could also be the switch .

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Old 12/08/07, 03:29 AM   #4
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The relay power is normally not fused it is the supply to to load that is fused.
Are you blowing the headlight fuse?
Look at the headlight wires.
Disconnect each head light see what happens.
What was the last thing you did before this happened?
you could have pinched a wire or it might just be a chaffed wire.
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Old 12/08/07, 08:32 AM   #5
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The relay supply is a fused 30 amp line.
I'm not blowing the 'headlight' fuse per se, it is the fuse on the load going to the relay.

The last thing before this happened was drive it normally, then it was parked for about 2 weeks.

I guess I will start by trying one of my other relays and see if it blows up...ugh, i hate it when the first 4 tries don't solve the problem...

Red 77: SOLD
Green 77: SOLD
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Old 12/08/07, 04:17 PM   #6
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so 14 fuses later i got no answers.

in short, I have HI beams, but LO beams blow the fused power line for the relay switch. Everytime. without fail.

I've pulled each plug at the lights, still hi, but lo blows. i've swapped relays, lo blows (and the relays work elsewhere afterwards), i've swapped ground wires, i've swapped dimmer switches, i'm dead in the water.

i just don't understand how i can have hi without lo? it's not the headlight switch since the hi's work, it's not the bulbs? could i have burned out BOTH headlight lo elements?


i guess i can bypass the relay and see what happens, but right now, i've given up, i'm going to let the ideas simmer for a while...

UGH.

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Old 12/08/07, 05:16 PM   #7
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OK, I'll take a stab at it.

Not knowing exactly what you have for headlight relays I'll be guessing and using a few assumptions. But it should be generally good.

There are probably 2 matching curcits. one for the low beams and the other for the high beams. The original wiring is probably turning the relays on.
I am guessing that the relays click on correctly for both low and high beams.
The fuses are between the battery and the relays.
So the curcit that is blowing the fuse is simply Battery-fuse-relay-low beams.
The fuse lives until the relay clicks in. So Battery-fuse-to relay is good. You have already swapped relays, proving that to be good.
The only thing left is the wiring from the relay to the headlights.

With both headlights unplugged does the fuse blow?
no-> plug in the headlights one at a time. When the headlight plugs in and the fuse blows, change that headlight
yes-> (this is what I suspect) there is a short in the wiring between the relays and the headlights. Pull out the headlight harness you dropped in and open it up. Start inspecting. I will guess that a wire chaffed against a sharp edge somewhere. At least you only have 2 wires to check and both are a short run. I had a short in the parking lights once. I broke down and started cutting wires to find mine. Cut off the front lights, fuse still blows. Patch wire. cut rear lights, fuse stays good. Cut left rear park light and splice the rear together, fuse blows. Fix left rear and start looking at right rear, cut it, fuse lived. Got home. Found a chaf where the wire turns and goes up to the tail light. At least yours is simpler.

Also, when you are done, replace the headlight fuse with a self resetting curcit breaker, 25 amp should be enough. If they ever short agian they will blink instead of going completely dark.
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Old 12/09/07, 09:26 AM   #8
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Quote:
Originally Posted by Broncobowsher View Post

There are probably 2 matching curcits. one for the low beams and the other for the high beams. The original wiring is probably turning the relays on.
I am guessing that the relays click on correctly for both low and high beams.
The fuses are between the battery and the relays.
So the curcit that is blowing the fuse is simply Battery-fuse-relay-low beams.
The fuse lives until the relay clicks in. So Battery-fuse-to relay is good. You have already swapped relays, proving that to be good.
The only thing left is the wiring from the relay to the headlights.

With both headlights unplugged does the fuse blow?
no-> plug in the headlights one at a time. When the headlight plugs in and the fuse blows, change that headlight
yes-> (this is what I suspect) there is a short in the wiring between the relays and the headlights. Pull out the headlight harness you dropped in and open it up. Start inspecting. I will guess that a wire chaffed against a sharp edge somewhere. At least you only have 2 wires to check and both are a short run. I had a short in the parking lights once. I broke down and started cutting wires to find mine. Cut off the front lights, fuse still blows. Patch wire. cut rear lights, fuse stays good. Cut left rear park light and splice the rear together, fuse blows. Fix left rear and start looking at right rear, cut it, fuse lived. Got home. Found a chaf where the wire turns and goes up to the tail light. At least yours is simpler.

Also, when you are done, replace the headlight fuse with a self resetting curcit breaker, 25 amp should be enough. If they ever short agian they will blink instead of going completely dark.

Thanks, I will try and search again, I checked the drivers side for chafes so far, but to get to the passenger side i'm gonna have to remove the batteries and their tray ....UGH

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Green 77: SOLD
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