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.
[attachment=0:id245ru2]fuelpump_relay_wiring.gif[/attachment:id245ru2]
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