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Brake lights blowing fuses. But why?


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The over all issue is my brake light fuse is blowing every time I hit the brakes.

 

I belive I chased the problem down to the passenger side light harness but I'm not sure where I go from her to actually fix the problem.

 

So with the harness plugged in (bulb or no bulb doesn't seem to matter) the fuse will blow.

 

With the green/yellow (brake light) power pulled from the harness. Fuse is fine and all other lights are fine.

 

I also get some crazy voltage ranges on the passenger harness some times ranging from 20 - 30 volt DC but not on the driver side. So a clue!.

 

Any help is appreciated.

 

'77 280z

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Sounds as though there's a short in your hot wire going from the switch (at the pedal) to the lights.  You could try to track it down (which may take a while), or you could run a whole new wire.  Not a very elegant solution, but certainly a quick one, if that's where the short is occurring.  You should be able to test the leads at the switch with a multimeter.  Check if you're getting 12+ volts at the fuse panel side; and check if there's continuity between either lead and a ground.  That may help narrow things down a bit.

 

Good luck with it.

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They worked before, then stopped?  Or they've never worked?  

 

Push the individual wires up through the bulb sockets, no bulbs, to make sure they haven't worked their way down in the socket to where they're shorting.  That happened to me once on the tail light circuit.  Insulate the wire ends and see if the problem is still there.  If it's gone, the source is in a socket.  If not, it's in a wire.  And, probably quicker and more effective to use a meter and test the power wire to see if it's shorted to ground.  You can do one socket at time that way.  Actually, you should do the test to ground before messing with the wires.  Just ID the brake power wires and test for continuity to ground.  Find the short them mess with the socket internals.

 

Don't forget to check the switch at the brake pedal also.  Might be broken and shorting when you press the pedal.

 

The 20-30 VDC is just odd, not really a clue.  Are you sure your meter didn't autorange to millivolts?

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