Thread: How to wire an electric fuel pump

Tweet

Welcome to CHR - hope we can help you out!

You are describing a Normally Open (NO) 12 volt relay. It sounds as if you have it hooked up correctly –
30 - should be a #12 wire fused at 20 amps to the battery (+ 12 Volts)
86 – should be a #16 wire to the switched side of the ignition, i.e., power when the key is on
85 – to ground
87 – should be a #12 to the pump

The image below depicts a standard relay. The “blue circuit” shows a square with a diagonal line running through it. This represents the coil circuit. The center numbers (86 and 85) are part of the coil circuit and will energize the the relay “on”. The relay will work when 12 volts dc is applied to these inner pins. If you follow the “red circuit” lines that extend from the outer numbers you will notice a gap in the line. This gap represents that these two pins are not connected or “Normally Open” in this circuit. The red circuit will close and allow voltage across it after the coil circuit is powered.

To test it apply 12 volts the coil (blue) circuit then place an ohm meter on the high amp (red) circuit. Select a low ohms or tone setting on your ohm meter. As the coil is powered you should see numbers close to zero displaying on the meter (or hear a tone indicating continuity). When you disconnect the 12 volts to the coil (blue) circuit the meter should show zero (no tone).

This will happen if the relay is working correctly. If not – the relay is bad.

Good Luck,
Glenn