---------------------------------------------------------------------------Tried this on another board, maybe I'll have better luck here-----

I've got a '98 F150 4.6L that won't start. Need some oldtimer ingenuity and insight. I'm going to assume anyone who responds knows what a starter relay switch is--if you don't, please don't respond because I don't want to hear about UFO's and sasquatch. Didn't even think about it when it happened--replaced the starter (the battery is brand new and fully charged). No dice. Here's the thing-- I then started jumping things out, if I jump (on the relay switch) the ignition stud to the hot post of my battery nothing happens. Good news, it's not the ignition switch or anything behind it in the circuitry. Now if I cross the two main posts on that relay, the starter will kick in. If someone turns the ignition key while I jump that relay, it'll start every time. Replaced that relay. No dice. I'm going to replace that relay switch one more time in the one in one-millionth chance that I got a bad one. Beyond that, gentleman, I am flummoxed. Any other ideas, O great gods of Ford wisdom?

 

A few things come to mind. First relay was bad and new one was also. Not likely but possible.
Bad ground at the relay.
Bad spot in the cable from the relay to the starter. Jumping directly between the two main posts might be giving it just enough extra juice to get through the bad spot.

If you can get a jumper cable from the relay to the starter to bypass or supplement the existing cable try that. If it works then you know you have a bad cable.
Is the relay at least clicking when you try to start it from the key or jumping it? If not it's the relay or the ground. If it is then most likely it's a bad cable.

I went through almost the identical thing awhile back. Ended up being the cable rubbed through halfway to the starter just enough to open the insulation and over time it corroded enough to cause the same symptoms.

 

There have been scattered reports of faulty starter relays out of the box. I learned a long time ago that the newness of a part does not gaurantee it's a good part.

To test the relay is simple:

Verify the relay's ground is intact (paint, dirt, packaging, etc) and the mounting bolt is properly grounding the relay's ground.

You should get switched battery voltage on the small terminal when the key is turned to START. If so, the relay should click. If it doesn't, it's bad.

If it clicks and the power isn't supplied to the starter-side terminal, the relay is bad.

Steve

 

One more question, and pour on the derision, poke fun, feel free with sarcastic remarks-- I'm a big boy, I can take it, in fact I enjoy it as long as it's clever. Keep in mind I'm not an electrician. When I put the new relay in, I did not mount it to the firewall, I just made all the connections. Are you telling me the relay itself has to be grounded and the firewall is the ground? If it's something that stupid, I'll give the first man who can make it over here a bright, shiny new quarter to walk up and knock the unholy ever-loving crap out of me. Don't say anything, just knock on the door and do it. I'll understand.

 

Yes. There are only three terminals on the relay. The coil's low side has to be grounded in order to have a complete circuit and to allow the relay to energize. That ground is provided by one or both of the relay's mounting tabs.

Hey, you've got a sense of humor and you'll never forget this oversight.

Steve

 

Thanks 089-- I mounted that switch to the firewall and vroom...vrooom.....vroooom. Except it's not a Volkswagen or whoever in the hell's irritating commercial that is. Thanks guys, you've been a lifesaver. However, I was a little disappointed with the lack of clever witticisms.

 

I was being a statesman. Usually, I reserve by best and sharpest comments for the really (genuinely) stupid, not someone who just made a goof due to lack of knowledge.

Good luck.

Steve