1979 fuse problems
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1979 fuse problems
recently bought a 1979 ford f250, 4wd, and when we turn on the heater/AC the fuse burns out. likewise, replace the lighter and as soon as we use any load on it, it burns that fuse out too. any suggestions on where to start? thanks!
MSEE
Joined: Apr 2004
Posts: 10,386
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From: Austin, TX
First verify that you are using the correct size fuses, which should be written on the fuse panel. If the fuses are the correct size, then the heater is likely shorting out because of a short to ground downstream of the fuse (which must be found by inspection) or a bad blower motor. The lighter issue may be that the lighter you're using draws too much current for the factory wiring (assuming the fuse size is correct).
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the fuses are the correct size, it just seems like a bigger electrical problem now that 2 different circuits are burning out. the lighter was replaced with an new socket and before I connected it, checked the power source with my volt-ohm meter and was getting 12V DC out.
MSEE
Joined: Apr 2004
Posts: 10,386
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From: Austin, TX
I've had issues with replacement cigarette lighters burning out the factory size fuse (assuming this is what you're doing). I think the newer ones draw more current than what these trucks were designed for. I wouldn't attribute that specific issue to a problem with the truck. Just don't use the lighter you're using. The heater would have to be a separate issue; the two circuits don't have anything to do with each other (from the factory, at least).
More Turbo
Joined: Nov 2006
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From: Great N/W
Since you have 2 issues with the same results, your idea of a bigger electrical problem may be accurate. 95% of ALL electrical problems are poor or missing grounds. I would start by verifying all the grounds, make sure they are making a good connection. Battery to block, block to frame, and block to body. The block to body one on the firewall is commonly missing, but an important piece.
Senior User
Joined: Jan 2008
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From: Irondale, Al.
Does the fuse blow at any fan speed? Mine would blow the fuse on high, later found a loose connection at the fan switch.
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MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
Highly doubtful, but you can easily check that by measuring the voltage across the battery terminals with the engine running.
