I'm having a problem with getting my 95 F250 to start. It has an E4OD automatic and 351. The relay on the firewall clicks once, then the truck won't start. I've searched here and other places and it seems as if it could be a lot of things. The battery is only 3 months old and I have a reading of 12.7 volts coming from it when I attach my voltmeter to it.

Yesterday, I replaced the "neutral safety switch" and it still does the same thing. I know the part goes by different names, but I'll use the popular moniker. I cleaned the terminals on the connector going to the neutral safety switch and have verified that it's adjusted properly using the procedure in my manual.

Here is what I've done so far.
With the key in the "on" position, I can use a screwdriver to jumper between the 2 big posts on the relay and get the starter to crank and start the truck.

I read somewhere that if you jumper between the small terminal on the relay and the red (positive +) terminal that it should turn the starter over. It didn't. It just clicked the same way it does when I try to start it.

While I had the small wire off of it's terminal (at the relay) I hooked a test light to it and put the ignition in the "start" position. The test light lit. So, it seems I have power coming from the switch to the relay.

I've seen various threads where people have replaced the starter, relay, neutral safety switch and still had the problem. Some replaced or cleaned the cables and that seemed to solve the problem.
I'm going to take the cables off today going between the starter and the relay and clean them really well before I go out and purchase any more parts that I may not need.

Anything else I could try to test the relay itself?

 

Just replace the starter relay on the fender with one from a Ford dealer and not an auto parts store.
You have done all of the tests.

 

With batt cables and ground straps if they are over about 10 or 15 years (in the rust belt esp.), truck not garaged and so on, it pays to just replace them.

Their problem is really the crimp itself and there corrosion can't really be effectively cleaned. The "big three" cables at batt, firewall, and frame can be replaced for about $20 in parts, made in U.S.A. by JC. If funds permit it's good practice to replace both the solenoid and bendix when replacing starter.

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That's been my thinking all along and should have replaced that before anything else. Since I saw how much corrosion is on some of the cables, I can't allow myself even think about letting that go. So, I'll do some cleaning and see how things turn out with that and go from there.

I'm even going to take the relay off and make sure it has good contact with the fender. That in itself could be a problem.

 

I cleaned all of the cables. No go. Went out and picked up and OEM relay/solenoid, installed it...she cranked right up!

Thanks for the help, guys!