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No difference Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Fri, 6 Jan 2006 05:07:20
In Reply to: Automotive Electrical Relay Q, Justin VanAbrahams  [Profile/Gallery]
, Thu, 5 Jan 2006 17:03:04
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To the relay, there is no difference - current is current.
The only considerations are in the circuit that is being driven and wiring.
So say you're going to supply a bunch of things, like headlights or tail lights. If you switch the positive lead, then each of those lights can have their 'low side' connected directly to a local ground. Less wiring. If you switched the low side, you'd have to have a fused power bus brought all the way to the back of the car, and then gather up all those grounds to a wire and bring it back. That's two thick wires instead of one.
If you're going to switch power to just one device, a relay to ground works just fine.
With the fog lights, they probably assume that the battery is close by; the kit probably includes fused wiring to tie directly to the battery. Since fog lights may be mounted out on a bumper, they will want to make sure there is a good ground for the lights (bumpers usually aren't). So bring the wire back through the relay. Since the relay has to be bolted to something (instead of flopping around), they assume you can find a good ground there.
If you know you've got good grounds for the fog lights, there is nothing wrong with switching the power to the lights.
posted by 192.249....
, Thu, 5 Jan 2006 17:03:04, Fri, 6 Jan 2006 05:07:20 <-- Viewing This Message, Fri, 6 Jan 2006 05:12:05
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