I got a relay from a friend that he had laying around. I don't know quite how to wire it. I have the wiring schematic HERE. I want to know where to connect the wires to and do I activate it by applying power or grounding it out.

 

85 and 86 are the coil. Hook either 85 or 86 to ground, it doesn't matter. The other one you didn't use will hook to a 12 volt switch or whatever you want to trigger the relay. If you ground one of these terminals, and touch the other to 12 volts, you should here it "click".

30 and 87 are the switch part of the relay. When you put power on the relay to make it click, 30 and 87 will become connected.

Relays are used to switch accessories that take a lot of current. You can mount the relay close to the battery, and run a large 10 guage wire to either 30 or 87. Using about a 30 amp fuse is good wiring practice to prevent fires. Put the fuse between the battery and the 30 or 87 connection. The other 30 or 87 connection will go to your electric fan, foglights, aux lights, or whatever you want to control. Here's a few examples of using a relay. Don't worry about the "nc" terminal on my diagrams. Some relays have this connection, some don't. In your case you don't have it, and it's not needed in any of the following examples.



This diagram shows how to feed a rv trailer power only with the truck keyswitch in the "run" or "acc" position.


This diagram shows how to add powerful back-up lights without burning up the original back-up switch on the tranny.



This is your standard foglamp wiring. Note how the 12 volt trigger for the coil is tapped onto the lowbeam wire. This is the legal way to wire foglamps in a lot of states, and is the way the factory wires them.

 

Thanks! I'm using the relay for my electric fuel pump so I don't put to much strain on my ignition switch.