No start possible wiring issue?

MATT MCCARRELL

MEMBER
1993 FORD F-150
5.0L
V8
4WD
AUTOMATIC
175,000 MILES

I've been helping my Dad troubleshoot his truck. It started with a dead cylinder. He changed the injectors and then it was two dead cylinders. Our neighbor used his injector test light and confirmed they are being triggered. Fuel pressure was then found to be low and the truck stopped starting.

He was sure it was a fuel pump and ordered one. He took the bed off and I was able to test the power to the pump. I found it was getting about 6V to the pump any time the ignition was on and didn't get 12V at any time.

He swapped the PCM for a reman unit. Truck is still in a no start state. A wiring diagram would be very helpful. Any suggestions on what to test would be appreciated.

Friday, August 1st, 2025 AT 4:06 AM

1 Reply

KEN L

MASTER CERTIFIED MECHANIC
54,137 POSTS

I can help you get it running NP. 6 Volts to the pump is a problem, you must get 12 volts, there is a inertia switch and the fuel pump control relay that must be checked first. Here is the locations, also, make sure the battery has 12 volts as well with the headlights on. This guide can help.

https://www.2carpros.com/articles/car-battery-load-test

The inertia switch is up by the firewall on the passengers side, this may need to be reset or it just went bad, please check for 12 volts here as well, (one wire), test with the switch unplugged. Here is the fuel pump relay location so you can swap it out. Check out the images (below). Please upload pictures or videos in your response of any problems so we can see what to help you with.

Images (Click to make bigger)