Relay question

[thiazole]

I'm wiring up a relay so that I can have a power source that turns on and off with the ignition. I'm just curious which is the "proper" way to wire a relay. So I'm going directly off the ignition switch wire - should I intercept that wire (ie, make that wire run through the relay) or is it ok to splice a wire off that source and go through the relay to a ground? I'd rather do the 2nd option, but am concerned that it would amount to a short - then again, the relay has an electromagnetic switch in it, so how is that any different than splicing a wire off to run any other low power accessory?

[yokotabrat]

A relay usually has 2 parts, an activation coil and a switch. You'll want to run the ignition wire to the coil portion of the relay and then the other side of the coil on the relay should go to ground. It won't be a short to ground because the coil has some resistance, therefore limiting the amount of current. It's the other side of the relay (switch side) that would be a short since it's designed to be low resistance. Hope this helps.

[thiazole]

Yep, that is what I was hoping. Thanks.

[Dane Becher]

Personally I would stay away from a critical circuit like the ignition circuit.

Remember that there are two different types of relays. 'Normally open' or 'normally closed'. Often a relay has 5 prongs and includes both NO and NC circuits. You just need to find the right set of prongs for your application (probably Normally Open). Pop the cover off and have a look at it. They are really simple to understand.

Here's an idea, take that relay and use a non-critical switched power (low current, rarely used circuit like cigarette lighter) to power the relay. Then use a heavy gauge wire directly from the battery (use a fuse as close to the battery as possible) through the NO side of the relay to whatever needs power. There, switched circuit, direct to battery, fused and all.:D

[thiazole]

The way I did it, I can easily change the switch source. As far as the power source, I used a 10 gauge wire directly off the battery. I also have a 10 gauge ground wire coming directly off the battery that goes to new terminal that is easy to access under the dash.

Good point on the fuse. I have a fused wire at home that I will splice into the power wire at lunch.

I've always been an idiot when it comes to wiring and I decided to learn the right way to wire stuff and fix all my old mistakes. My Talon is wired completely wrong and when I feel confident that I know what I'm doing, I'm going to redo all my wiring on that car (I'm amazed that I don't blow fuses all the time). The wiring I'm doing now is on my Escape. I need to do some wiring on my diesel truck as well - I want to wire up an EGT and boost gauge and I'm also thinking about buying a "rear view mirror camera". It sits so high off the ground, I'm afraid I'm going to run over one of my neighbor kids backing out of the driveway. It could also be useful when I'm hitching up or pulling the trailer.