Hello,

I have a 1990 Ford F-150 XLT Lariat (5.8L, E4OD, 4x4). Last week, the alternator died. After replacing the alternator, the truck will crank, but will not start.

I tested the fuel pump and discovered it’s bad (makes sense, being a cheap Amazon fuel pump I put in it to get it home a few months ago when I bought it), so I bought a new fuel pump modulator from O’Reilley’s since the sending unit is still fully operational.

Upon testing the pump, nothing happened. I checked for voltage at the pump and got 6.87v. Simple, right? Check the fuel pump relay, continuity and input/output voltage are present. Checked the fuel pump selector switch, and I’m getting 5.6-6.47v. Go further back in the system, check the ignition switch. All wires produce voltage minus the red/light blue output wire. Cool, bad ignition switch. Go to autozone, buy a new one, plug it in, do a voltage check, 0v still. So I check the inertia switch, not tripped, bad input voltage. Check the fuse link coming from the starter solenoid, and it’s not there. Replace it, and still having the same issue.

All of my grounding wires seem to be in order (not overly corroded), same with all of the wires coming into and going out of the FP relay and EEC relay, as well as the wires going along the frame towards the fuel tanks.

Neither fuel pump worked when I bought this truck, so I replaced the rear pump and ran off of it for a couple months.

Any ideas on where else I can check? I’m starting to pull my hair out about it. Thanks!