So im trying to rewire my pump to run driectly from the battery. i bought a 40amp relay used for aftermarket lighting. 4 prongs, from the battery, ground, from switch, and to pump.

i hook it up and no power to the pump. i'm getting 12.1 volts to the relay, ground is good.......heres the kicker....... when i dont have the wire connected to the relay, i am getting 11.3 volts from the switch or the stock power to the pump but when i hook it up its only showing 5 or 6 volts when hooked up the the relay and no power output at all to the pump. i went and bought a new relay the same one and got the same results. any advice is greatly appreciated.

 

Sure you have the wires on the correct prongs of the relay?

 

yea. do i need a 5 prong?

 

4 prong should be fine. i think you have the wrong prongs wired.

 

when the original power wire goes live thru the relay ie 86, then the relay goes hot and allows the new power line that goes to 30 to pass thru to 87 and hit your pump.

 

I just did this rewire and used a 4 prong relay. Works fine. Wired it exactly like Camuman's diagram above.

 

Recheck your ground and make sure it is a good ground. This is my best guess.

 

found the problem. i found the power i was tapping into wasnt original power to the pump but another power source in the plug i guess for the fuel level. thank guys