OT: car electrical wiring ?

eric · Since 13 Jan 2006 1871 Posts XTreme Poster

Putting an aftermarket seat warmer in my Subie. It draws 3-5 amps max. I looked in my other car with factory seat heaters to get an idea of what circuit to use. I noticed that there are two circuits--fuses--associated with the heaters. One fuse location is labeled "seat heater relay" and there is another 15 amp fuse labeled "seat heater."

I am assuming that the relay is a power junction for several circuits, and the fuse labeled seat heater is to seats only. Sound right?

Nak · Tue Jan 22, 13 7:02 pm

Get yourself a real shop manual. Not Chiltons crap that you get at auto parts stores. Ideally, go to the dealer and get whatever the official Suburu manual is. Ebay can be a good place to pick up manuals cheap too. Just make sure its an official manual. Then, look at the wiring diagrams.

If I were going to wire in a new circuit, I'd tap off the battery, or better yet the 12v bus if there is one. The 12v bus would most likely be on the firewall, and have a direct feed from either the alternator or the battery. Several circuits will draw right off the bus. Use an inline fuse as close to the bus or battery as possible.

If the heater is only going to draw 5 amps, you don't need a relay. Don't expect a 5a heater to heat quickly or strongly though. You're looking at 70 watts at 14 volts.

Hopefully, your heater comes with an inline fuse. If it does, use it. Any extra wire you use needs to be at least as large a gauge as the supplied wire. If it doesn't, google what wire gauge you need for 20 amps. 12 gauge I think? that's off the top of my head though. Fuse it at 10 amps. That'll give you a nice safety margin. The 12 gauge wire will have very low power loss, so you'll get maximum power at the heater.

Hein · Since 08 Mar 2005 1314 Posts Possessed

http://forums.nasioc.com/forums/

quick search and found this:

dangler · Since 26 Feb 2006 1781 Posts WINDY SPOTS XTreme Poster

this is my new low tech, high maintenance seat warmer...