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Ecarlcl · Oct 2, 2005

I have a 90 XJ 4.0 5 Speed

One day the blower motor started to blow it's fuse. I have had it apart ever since tracking down the short.

It goes:
battery->red wire -> ignition switch -> brown wire -> fuse block -> purple wire -> hvac control

I have isolated the short to the brown wire that runs between the ignition switch and the fuse block. (with the ignition switch unplugged and the blower fuse removed) So I try to splice in a new wire there as opposed to going completely through the harness to locate the short and even on the new wire I still read a short. I'm stumped. At this point I'm considering going to the boneyard and getting a whole 'nother harness.

Anyone know whats up?

Thanks

Ecarlcl

langer1 · Oct 2, 2005

If the blower fuse it blowing, it can't be the brown wire causing it, because it's before the fuse. To blow the fuse the short has to be after the fuse block.

Eagle · Oct 2, 2005

langer1 is correct. Any short upstream from the fuse won't blow the fuse, it'll just fry the wiring.

I also notice that your wiring schematic stopped at the HVAC controls. This suggests that you are assuming there can't be a problem between the HVAC controls and the blower motor. Don't forget that the wiring goes from the blower switch through a resistor pack ... that's what controls the fan speed. Those resistors sometimes fail. Usually they fail to an open circuit, but it's not impossible (I suppose) for one of them to short out.

I'm afraid you need to trace your ENTIRE circuit, not just the first half.

BTW -- have you unplugged the blower motor itself and hot-wired it to test motor function? It may be as simple as the motor itself siezing up.

Ecarlcl · Oct 2, 2005

Eagle said:
langer1 is correct. Any short upstream from the fuse won't blow the fuse, it'll just fry the wiring.

I also notice that your wiring schematic stopped at the HVAC controls. This suggests that you are assuming there can't be a problem between the HVAC controls and the blower motor. Don't forget that the wiring goes from the blower switch through a resistor pack ... that's what controls the fan speed. Those resistors sometimes fail. Usually they fail to an open circuit, but it's not impossible (I suppose) for one of them to short out.

I'm afraid you need to trace your ENTIRE circuit, not just the first half.

BTW -- have you unplugged the blower motor itself and hot-wired it to test motor function? It may be as simple as the motor itself siezing up.

The motor is fine, new last spring, I'll check everything again and see what happens. Thanks

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Ecarlcl

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langer1

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Eagle

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Ecarlcl

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