I had to replace the headlight switch for my car not too long ago, and since the correct switch is $120+ (that’s with a discount!), I bought one of those generic switches and installed it. I had to rerun the wires to get the thing to work, and I used 16 gauge automotive wire. This worked for a while, but now the wires are getting hot and the insulation’s starting to melt near where the wires connect to the switch. So, obviously I need to use a heavier gauge wire, but what? The wire I’m using appears to be thicker than what came with the car, so I don’t understand why its not working. To top it all off, I’m going to have to rewire the heater motor here shortly, and I need to know what gauge wire to use before I undertake that. I really don’t relish the thought of the dash going up in flames on me in the middle of winter! Any suggestions?
I don’t think wire gauge is the issue here. Melting insulation near the contacts sounds like a bad connection. If the wire were too smal, it would hot down its entire length.
Unfortunately, your best bet would have been a salvage yard. Relays and switches can get incredibly expensive from a dealership, but are usually pretty cheap in the wrecking yard. A U-Pull-It yard is usually by far the cheapest.
Well, the heat is certainly making its way down the length of the wire. Would have gone to a scrapyard, but around here, they’re all closed on Saturdays! (Why, I have no idea. I guess they don’t think that people’s cars break down or get fixed on the weekends.)
Maybe I’ve just had bad luck. But everytime I’ve bought a part from the wrecking yard I’ve regretted it. Nearly always, I’ve ended up having to buy the new part anyway. I think this would be especially true of an electrical part.
Well, you didn’t specify what kind of car it is, but you do have one fairly easy fix: Wire the car so that the headlight switch runs relays, and the relays run the headlights.
Someone mentioned a site here on the SDMB recently, that concerned headlights, and it had a clear, easy rewiring diagram.
After that, the headlight switch itself will only pull a small amperage. All the real juice will be going through the relays.
I had a '69 Charger way back when. The headlight switch had a circuit breaker built in, as well as the vacuum switch for the headlight doors. The 'breaker was old, and tended to “blow”, especially after I plunked some halogens in it.
I rewired it for relays and not only did it stop “blowing”, but the lights were far and away brighter, since there was less resistance through the system.
The other thing to look for in your redo job, is the connections to the switch. Did you patch in wires using solderless “butt connectors”? Did you just twist and tape 'em? Did you adapt the new switch’s plug terminals using crimp-on spade connectors?
You can lose a lot of the resistance- the source of the heat- by properly soldering all the connections, and using the correct switch “loom” or molded plug.
I’m looking at a table that claims that high beams draw 13 to 15 amps, and low beams draw 8 to 9. You need 12 gauge automotive primary wire for 24 amps (up to a 10’ run), and it wouldn’t hurt to run 12 gauge.
Even after saying that, I’ll agree that it sounds like the resistance is coming from the switch or connections.
Checked the wiring and the connection is definately loose, so I’ll have to fix that, and hopefully that’ll correct the problem. Is the 16 gauge too light if I have to rewire the heater motor connections, or can I get away with using it? (The car’s a 84 Honda Accord, BTW.)