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Discussion Starter #1
Hey all,

I am trying to get my heater hooked up and working. The wiring in the car looks to be in pretty good condition but certainly not perfect. The heater fuse keeps blowing as soon as I turn the ignition to the "on" position. I have completely disconnected the heater blower and the switch from the heater box resistor just for good measure however the fuse still blows instantly once I turn to the "on" position. My guess is that I must have a short in the harness somewhere between the fuse box and the firewall connector. Would I be correct in my assumption or could something else be blowing it ? I don't really see anything else on the circuit that could be blowing it but I don't want to start tearing apart my harness quite yet until I have ruled out other possibilities. Thoughts ?

Thanks !!
 

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Get a multimeter and unplug from the heater switch. You should be able to see it it’s going to ground and shorting.


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Have you disconnected the heater blower motor feed itself? The heater blower motor is "hot" whenever the key is "on". The switching of speeds occurs on the "ground side" of the circuit. You could have a short anywhere from the fuse box out to, and including, the blower motor.

Note: The schematic shown about is for a '68 which is not wired the same as a '65-66.
 

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So it's blowing with no load on it.
Did you check your fuse terminals for corrosion. Could have some rust up in there tracing to ground

Some contact cleaner And a wire brush will clean it up

Disconnect battery first and might as well do the other terminals as well
 

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Rig up a cheap 21W bulb & socket with 2 wires & connect to the fuse terminals instead of the fuse that keeps blowing. Switch on the ignition & as long as the bulb lights will full brightness you have a short. Trace/wiggle the heater wires & associated harness & when the bulb flickers or goes out you have found your short.
 

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Discussion Starter #9
Thanks for the replies and schematics although I have them already. Yes...it is blowing the fuse with no load on it. Both the blower and the switch are completely disconnected. The engine gauge wiring harness is brand new so I don't think there is a short there. So if there is nothing else on the circuit then the short must be coming from somewhere in the fuse box or the wiring harness going from the fuse box to the firewall I guess. The fuse box has some corrosion on the terminals but it's not horrible. The fuse box is also not mounted to the inner side wall. It's just hanging down. So with all this being said is it fair for me to assume that the short is somewhere in the harness from the fuse box to the firewall ?? I am hesitant to start pulling the harness apart before looking at all other possibilities. Are there any other possibilities that anyone can think of ?
 

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Discussion Starter #10
After taking a closer look at the fuse box...it looks like this needs a good cleaning. Do you all think this could be the cause of the short ?
 

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Could be but even if it’s not the root cause that box and terminals really needs a good cleaning. To find your short, pony gaz is giving you some good advice.
 
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