Is there a problem with using ground side switching on a heater blower motor? I have to add a ground wire because my heater box is fiberglass, and I am rewiring the whole car right now anyway. Also, could I use a headlight dimmer swith on the ground side to make the fan variable speed?

Thank You

I would just establish a good ground for the motor and switch it like it was made to do originally. If for no other reason than to avoid confusion in the future after you forgot, or sold the car and no one can figure the circuitry correctly. It should also be fused on the + side for consistency. FWIW.

One tradeoff with using ground switching is that it increases the risk of electrical shorts because more of the wiring is always hot.

The advantage is when you want multiple switches to turn the circuit on. Like any door switch turning on your dome light.

For a heater I would probably wire it like original because it makes for a lot less wire involved in the circuit. With the power switching you do not need a seperate wire from ground running all the way back to the switch. Shorter wires are good wires ;)

I could make it like everyone elses, but I choose not to. I have nothing against convention, but I place a higher premium on originality. I would like to have a infinately variable speed fan on my heater. Is ther any reason why a dimmer switch wouldn't work after the load?

Thank you very much.

You know there are often good reasons why things are done the way they are. I love to do things differently as well but recognize that there really should be a point to doing so.

But if you insist on having 2x the wire in your heater blower circuit and the detrimental side affects you may.

Regarding the dash light dimmer... you will need to compare the current and power ratings and demands. The dash lights probably pull less than 1 amp so the rheostat needs to dissipate something like 12 watts. Your heater blower probably pulls 5-10 amps so a similar rheostat would need to dissipate 60-120 watts. Every see the size of a 60-120 watt resistor? Might be why the factory put resistor loops inside the air duct where moving air could cool them. But then what did they know that you cannot screw up better? :clonk:

I thought I was cordial with my reply, if argumentative. I appreciate your knowledge if not your bad attitude. I can make goofy faces too.

Besides, I was actually responding to the post above yours.