Wiring 47 Ford Car Heater Motor

C

Clrascoe

Junior Member
Does anyone know if it is OK to connect the heater motor to the accessory post on the ignition switch? I have seen information both ways. My car is still a 6-volt positive ground system if that matters.
 
In my opinion that would be too much amperage draw, and would risk melting the wires to your ignition switch. A better option would be to run a wire directly from the battery with an inline fuse through a switch to the fan.
 
Thanks Gregory. That’s what I was concluding. Any thoughts on what amperage fuse to use or how I can find out?
 
my 46 had a heater that was connected to ignition switch— that ignition switch had 2 contacts and one of the studs was broken off with everything hooked to the single stud and no issues from that during my ownership.
connect it and after using it feel the switch— if it is getting hot it is working too hard for it or it needs cleaning
 
I'd wire in a relay of adequate amperage, maybe a 20amp. Your heater switch would act as the switch that actuates the relay coil with the power from a battery source wired to the heater motor.
 
There are relays that conduct 40 amp loads.
I use old Bosch ones, a one inch cube.
They take a minimal amount of power to operate and hold up well.
Your switch could operate more than one.

Karl
 
As shown in the attached wiring instructions, the heater is connected to the fuse block in the firewall for power. A relay would be a good option if you want to have it switched from the ignition switch. The heater will draw too much current through the Ign. Switch and cause premature failure.
 

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meric42 said:
As shown in the attached wiring instructions, the heater is connected to the fuse block in the firewall for power. A relay would be a good option if you want to have it switched from the ignition switch. The heater will draw too much current through the Ign. Switch and cause premature failure.
Click to expand...
0006994_heater-motor-wire-car-1939-1940-91a-18457.jpg

See > https://www.joesantiqueauto.com/heater-motor-wire-car-1939-1940-91a-18457
0006945_heater-motor-wire-car-1939-1940-91a-18457.jpg
 
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I'm in agreement with the relay. The ignition switch turns on and off the relay which does not take that much power to operate. The relay, once it's turned on gets its power directly from the battery to the heater circuit. This way only a little voltage is going through the ignition switch to operate the relay. The relay is then providing the heavy current from the battery to the heater. There is less chance of burning up an ignition switch, and when you turn the key off it will shut down the heater relay off, so you don't accidently leave it on. This is the way modem cars are wired. Anything that takes a lot of current usually goes through a separate relay.
 
So a person would run a wire from the battery with a inline fuse to the relay then to the heater switch ?
 
coolcoupe said:
So a person would run a wire from the battery with a inline fuse to the relay then to the heater switch ?
Click to expand...

You will need two relays. One for the heater and the other for the defroster. The diagram is for 6 volt positive ground wiring.

590471
 
About that time period I believe heaters were an option on new cars and I believe the dealers usually installed and wired them. My '47 was wired of the ignition switch. The insulation on the heater wire under the dash board wore-thru and sparks were flying. As suggested I put a relay on the fire wall in the engine compartment to operate the heater - gets that high amp wiroing out of the passenger compartment.
 
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