Thread: Let's talk about Relays

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All of the points made by Rrumbler and Pat are good ones. There are times when one needs to have a ground activated Relay. Some remote control devices only provide a switched ground output and your source may need to have a switched power to it. Also on some power window setups, the switch controls the ground and not the hot lead so in these cases, it too makes sense to control the relay with a ground wire.

Like Rrumbler said, sometimes it is just easier to wire the relay using the ground wire as grounds are easier to find. Also, since your relay needs to have power (B+) anyway, you only need to run one power line to the relay. Oh and... ALWAYS... make sure that your B+ line is fused. I once missed that one tidbit and had a wire glowing bright red before I cut it. Then I had to start wiring all over again.