Need Help With 1966 Mustang Heater Problem

NEPAFM

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Feb 25, 2020
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Hello,

I need some opinions on what the heck has been holding up my Mustang rebuild project for the last three weeks. I recently installed a new heater box, resisistor, and heater motor into my 1966. For some reason, as soon as I turn on the ignition the fan motor kicks on and will not shut off. I can move the three speed switch in any direction and it doesn’t stop running. I tried to unplug the resistor and it still runs. If I unplug the brown wire heading into the heater motor, it stops running. Any help is greatly appreciated!

thank you!
 
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Billm

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Apr 16, 2014
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Time to get a wiring diagram and start tracing your wiring and find why or where the brown wire is hot.
 

Olivethefet

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May 17, 2018
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Yeah, you've definitely got something wired wrong. Do you have a wiring diagram as suggested? The system isn't that complicated. Pictures of how it is currently wired up might help as well.
 

NEPAFM

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Feb 25, 2020
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I did purchase a 1966 shop manual, which includes a diagram. If the fan has power all the time there’s no reason it would be the ignition switch or heater control switch right?
 

NEPAFM

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Feb 25, 2020
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All the wires are correctly hooked up that’s what is so frustrating. Red wire from battery to solenoid, black yellow from solenoid to fuse block, yellow to back of ignition switch, black green from ignition switch to fuse box, brown to heater motor. The only things that arent new in the whole loop is the ignition switch and wires from heater control to resistor. It makes me think one of those two are bad but it’s probably the wires themselves somewhere.
 

Billm

Member
Apr 16, 2014
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It sounds like the heater motor has constant power. It might be from the constant power terminal on the ignition switch post or the fuse block. Check the diagram and find the blower motor wire coming into the car thru the firewall Andy see where it goes under the dash.
 

Zeeks Stang65

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Nov 18, 2019
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Not to steal the thread but I have a 65 and I am having trouble getting heater core out. AIready opened up heater box and removed front but core doesnt want to come loose. Any help is appreciated. Thanks
 

NEPAFM

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So I had an extra wiring harness when I bought the car. I replaced the old harness with the new harness. ITS STILL NOT WORKING. Do you think it could be the ignition switch? The fuse block was replaced with the new harness.
 
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