How do I wire a fuel pump relay?

Analog ECU Superjection
Fuel pump relay wiring diagram

The practice of wiring the fuel pump through an external relay has two objectives:

  1. To protect the computer from over-current damage. (Some circuit traces inside may burn open if a pump or other component has problems. This is an expensive failure to repair).
  2. To minimize voltage drop to the fuel pump. (Small gauge wire, switches and/or long runs to the pump may cause a drop in the power needed to run at full output).

Use a Bosch relay 0-332-204-150, or a standard 12V/30 amp. automotive style single pole, double throw with the terminals marked 30, 85, 86, 87, 87a.

  1. Mount the relay in a suitable place on the firewall. A socket for the relay is okay, or just use push-on terminals.
  2. Use the red fuel pump wire from the computer to activate the relay through pin 86. Ground pin 85 to the chassis.
  3. Find a +12V source capable of supplying at least 15 amps, such as a terminal block on the firewall, or even directly to the battery. Install an in-line fuse of 10-15 amps and attach to pin 30 of the relay using 12-10 gage wire.
  4. Attach a 12-10 gauge wire from pin 87 (the normally open contact) to the (+) terminal of the pump. Ground the pump (-) terminal to the chassis using 12-10 gage wire.

The computer will turn the pump on and off as before, and allow it to run at full power.

See also "Can the fuel delivery system have good pressure, but still have a bad pump?"