What's the third terminal on the starter relay for?
 

'96 F250 7.3L PSD 4x4

I went out to start it the other morning, and got no response from the starter. Here's what I know:

• The 'Wait to Start' light & all other lights came on & went off as expected, except the battery light, which stayed on
  
• The batteries are fully charged, and there is no corrosion on any of the posts.
  
• I heard all the normal clicks
  
• I can still start the truck if the key is in the ingition in the 'engine on' position and I short out (hotwire) the two main terminals on the starter relay

There's a third, smaller, terminal on the starter relay with a push-on connector on it. I suspect that the wire connected to that terminal is a lead from the ignition switch that's supposed to signal the relay to divert power to the starter, but I don't get any voltage through that lead (not even when turning to the key to the start position).

Here's what I want to know:

Am I right about that third terminal on the relay? If so, I don't think buying a new relay will fix my problem. Since I get no voltage into that third terminal I'm assuming there's a short in the wire connected to it, and the relay never gets a signal to close the circuit to the starter.

I suppose I could just pay the $25 or so for a new relay & find out if that fixes the truck, but I live in the country & don't want to drive all the way to a parts supplier just to pay for something I'm not sure will fix my problem...

Any help would be really appreciated!

Welcome to FTE. I believe you are correct about the third terminal. Did you check the wire, and how about the ignition switch itself?

no, I didn't check the cable or the ignition yet...
 

it never occurred to me that the ignition switch might be the problem....I'll give that a try first. The cable into the relay is wrapped into other thick groups of wires...looks like a pain to expose it all the way back to the starter. I'll do it today though if the starter seems to be ok.

--thanks

If it is the wire, just cut it at both ends and replace it.

ok - the ignition switch is fine. The wire from the switch to the relay is also fine - there's no resistance between the switch and the relay. So, it must be the relay, plain and simple. The lowest setting my voltage tester has is 15 V (will pick up anything from about 5 to 15 volts), so I figure the signal sent from the ignition to the relay must be less than 5 volts and that's why I couldn't see it.

I'll post another reply once I get the new relay...

OK - bought & installed a new starter relay, and it didn't fix the problem. I'd turn the key to start it and still nothing.

So I knew it wasn't the relay, wasn't the starter (I could still hotwire it), wasn't the ignition switch or the lead from it to the relay. Frustrated I went back to my shop manual's engine wiring diagram to make sure I hadn't missed something.

Turns out I had missed something...the clutch position sensor switch. I looked at it and noticed that the switch assembly had slipped off a small retainer bracket. I put it back on, and bingo, problem solved.

Now the only problem is I have to drive all the way back to the parts supplier to return the relay! :o