Posted by David Sherman on Sunday, November 25, 2007 at 21:35:49 :
In Reply to: Starter Relay posted by Brett in AK on Sunday, November 25, 2007 at 14:28:57 :
One of the great things about doing your own wiring is you can use a lot better components than the factory uses. It makes a big difference to Ford or GM whether the relay costs 29 cents or 27 cents. They multiply it by millions of vehicles and multiple relays per vehicle and the bean counters come up with a meaningful number. But if you're doing your own stuff, the difference between $5 and $10 for a really isn't even worth thinking about. The main things are that the relay, and the switch and everything else in the system, be reliable and foolproof so that it works right the first time and you never have to replace anything.
I also agree about soldering the crimp terminals and using screw-down terminals on switches, relays, etc rather than spade terminals when there's any serious current involved. 10 amps or so is my threshold. Below that, I'll just crimp them or use spade terminals, but above that, it's solder and screws for anything serious.
The main problem with the spade terminals is that female part relies on its springiness to make a good connection. If the connection isn't absolutely perfect, and there's a lot of amps going through it, it will heat up. Heating anneals copper to a soft state, at which point there's no spring to it any more and the terminal just gets hotter and hotter. I've seen more loose, charred spade terminals over the years than I could possibly count. In no case was the circuit "overloaded". The problem was just that the connection was poor, and as soon as it started getting hot, it got worse fast.
Using separate relays for each set of lights, as you described, has another benefit: If one circuit goes bad for any reason, you still have some lights.