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I recently purchased a used 1991 F-150 from the original owner. As soon as I got it home it wouldn't start immediately after I shut it off... after some reading the first thing I suspected was the fuel pump... I grounded the test lead of the test harness as suggested by the Haynes manual and the fuel pump came to life... the truck then started and I used this method a couple of times again over he next few days when it would not start... for the last 2 months it has been starting, and running, just fine (without grounding the test lead)...

For the last two weeks I was away and did not start it. Also it has been below freezing lately... well below for some days, but now its in the 20's & low 30's F.

I tried to start it yesterday, but it wouldn't catch. I did not hear the whirr of the fuel pump so I tried grounding the test lead again. This time the pump did not energize... I removed the fuel pump relay and jumped the switched pins... the fuel pump came to life... so now I'm confident that the pump motor is fine as well as the inertia switch. I replaced the relay with a new one, but the pump still did not work. The relay control pins showed 5V across them.

So... my question is... what voltage should appear across the relay control pins? What else can I test in this circuit?

All advice appreciated!

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