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mejulihn's Avatar
 
Join Date: Nov 1998
Location: Camino, CA
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Electrical glitch

A mysterious cross connection has suddenly manifest itself in my electrical system. When I turn on the headlight light switch, the fuel pump cycles. It also cycles normally with the ignition so that's just strange. Also, when I step on the brake or turn the lights on, the voltmeter drops to zero and the oil temp gauge pegs on the high side of the scale. Any ideas on a common source?
Old 09-20-1999, 12:15 PM
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This is just a WAG, but you might have worn through the insulation on a wire and be shorting to ground, perhaps close enough to the fuel pump to drive it. Is your pump located in the front or elsewhere? Front mounted pumps (like mine) have a relay wire running through the center tunnel and up under the dash which might bring them close enough to your lights / brake wires.

I'll go take a peak after work and see if anything looks likely (no carpet installed yet).

Old 09-20-1999, 01:14 PM
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Check you fuses for minute cracks or missing fuses. It sounds funny but this actually happened to me.
Old 09-20-1999, 01:37 PM
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Jim is right, check the 4th or 5th (forget which) from the right side of the fuse panel. probably blown or old or loose. Make sure you have one of those un-obtainium fuse covers if you tend to kick them like I do getting out.
Old 09-20-1999, 01:49 PM
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I will start with the fuses. And thanks, John, I do have a fuse panel cover to prevent an errant knee from dislodging a fuse!
Old 09-20-1999, 05:36 PM
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Well, I checked fuses and they all look good. Obviously, I have a cross connection in the lights, brake, hazard flasher, and fuel pump circuits. Since all the lights (headlights, parking, hazards) work normally on the front of the car but not the rear, where should I look next??
Old 09-24-1999, 07:14 PM
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This is an interesting one. Could use a few more facts though.

1) What year is your car?

2) Where is your fuel pump? If up front, has it always been there or was it relocated (makes a difference concerning tracking wires)

3) Least likely, did you anytime recently install new voltmeter or oil pressure gauges?

Fuse 5 and 6 from the left are for the rear lights, but there's more:
The wiring diagrams show a RD/WH power lead terminating at the voltmeter, after passing through and providing power also to the oil pressure gauge, and apparently coming from the brake lights switch under the brake pedal [I'd call that something of a link]. This is the end of the RD/WH wire, now connecting to a terminal with two other wires, one GY/BR heading for the rear of the car and responsible for power to the light in the engine compartment, travelling through the Relay Plate, and one BK/YW going to fuse 9 for power (there is also another BK/YW wire separate from these, travelling to the tail lights--to keep things straight).
I would check that brake light switch area under the brake pedal, and the situation of the RD/WH wire and other wires mentioned. If your pump is being affected, I'm guessing that thing has to be up front, so look for a place where it's power lead nears these wires. Only other thing I can think of secondly is the headlight and hazard switches, which are both a mess of wires connecting many aspects and just waiting to go wrong. --john
Old 09-26-1999, 08:59 PM
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BTW, my explanation was based on year 73 diagrams. On my 71 the lead BK/YW from the fuse panel to the brake light switch under the pedal comes from fuse 8, counting from the left.
Old 09-26-1999, 09:11 PM
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Eureka -- I found it! The problem was traced to a loose ground connection for a cluster of ground wires in the left front corner of the engine compartment below the relay board. This area is very hard to visualize and I had to remove the cabin heating fan to get a good look.
Old 09-27-1999, 09:06 AM
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