Heater box resistor missing

David A · Jul 27, 2019

When I bought my 65 Mustang coupe there were several bonus items that came with the car . One of them was a new heater box and new seals. I was getting ready to install it in the car and noticed that there was no resistor on the box where one should be. It doesn’t even have holes to put one on. Can I just use a cutting bit and make one? I would also have to drill 2 screws for mounting holes. By the way does that resistor connect to anything on the inside of the box? From pictures I’ve seen it doesn’t look like it. What does the resistor do anyway? By the way it is a later 65 so it has a 3 speed switch.

Olivethefet · Jul 27, 2019

I cant remember how its wired up, but I'm pretty sure the resistor is used to drop voltage for the low speed of the fan. That's what it was used for in my old Bronco anyway.

David A · Jul 27, 2019

But it’s not connected to anything inside the box right? I just don’t see how that controls anything. I know I’m missing something here .

Olivethefet · Jul 28, 2019

I'm working off memory from years ago here so I apologize if I get something wrong. On my 76 Bronco and my dad's 65 mustang they both had two speed heater fans. In my bronco the resistor broke and I couldn't just buy a new one. Couldn't find one for sale. At the time some electricians friends helped me fabricate a replacement using wire. I dont remember the wire type. It wasn't just copper. What we made ended up just being wire coiled up in enough tight loops to provide the proper voltage drop. This then mounted to the heater box with the coils inside the box. They get hot when in use so this kept it away from everything and the air moving in the box helped keep it cool. There were blade connectors sticking outside of the box for the wiring to attach to.

The wiring harness for the heater circuit allowed the speed control switch to either send current straight to the fan, high speed, or through the resistor, low speed.

In short the resistor didnt hook up to anything in the box. It was just mounted on the box.

Did your car come with a heater? If it didnt you might have to find a wiring harness for it.

Again, I'm no expert on this. I hope this helps you out. I have limited internet access at the house but when I get to work tomorrow I'll try to find a picture of what I'm talking about.

Olivethefet · Jul 28, 2019

I found this post in the classic mustang area.

Heater Resistor--1965 | Mustang Forums at StangNet

Heater Resistor--1965

I am trying to track down the wiring for my heater. It is on all the time...and I have no switch....so I believe it is hot wired. SO...I am starting from scratch on the wiring... When I look at the switch..I notice it hooks into the resistor (as best as I can tell). From what I can...

www.stangnet.com

Is this the resistor in question?

I also found this wiring diagram. It's in the thread that I listed above. This is a diagram for a 3 speed fan, but it should give you a good idea of what is going on.

horse sence · Jul 28, 2019

Probably a 64 1/2 heater box ,they do not have it in the box ,it is in the back of the switch assembly

70mstang · Oct 3, 2022

no it's not wired to anything inside the heater box, I think they just decided to keep the resistor coils inside for simplicity's sake... maybe to keep them cool. the connector from the wiring harness goes on the non-springy side

Heater box resistor missing

David A

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Olivethefet

I will own your nuts! LOL

David A

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Olivethefet

I will own your nuts! LOL

Olivethefet

I will own your nuts! LOL

Heater Resistor--1965

horse sence

70mstang

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