Starter will not engage unless I jump across the two 12V studs?

DAN TARR

MEMBER
1991 FORD F-250
7.5L
V8
2WD
MANUAL
127,000 MILES

If I turn the ignition to "start" the starter is inoperable. If I leave the switch in the run position and jump across the two studs on the starter solenoid (on the passenger side fender) the starter engages normally, and the engine starts and runs fine. Is there an additional starter relay (NAPA sells one for this vehicle), where is it located? That and a bad fusible link is all the possibilities left, I think.

A little more background info:
The start system was working fine. During the last drive however, the truck overheated due to a stuck thermostat (since replaced). Due to the overheating condition, the truck was shut down to prevent damage. However, when attempting to restart after it cooled down the engine was too tight, as if it partially seized up. (The serpentine belt would only move about 3-4 inches before it stopped.) Numerous attempts were made to start the vehicle while waiting for a tow. However, now that it is fully cold (and the next day) the starter is inoperable using the normal ignition switch.
As noted above, the engine cranks normally when bypassing the solenoid. I've driven it 15 miles since with no other issues.

Wednesday, January 29th, 2025 AT 11:55 AM

1 Reply

CARADIODOC

MECHANIC
34,180 POSTS

The first thing to check is if the ignition switch shifted. It's on the steering column and is adjustable. The photo shows the two slotted mounting holes. It's somewhat common for them to work loose and move under spring pressure, then the key cylinder won't turn quite far enough for the starter circuit to engage. The two mounting screws commonly have 5/16" hex heads.

Next, have a helper turn the ignition switch to "crank" while you check for 12 volts on the red / light blue wire on the starter relay. Use an old-style test light if possible as they can be more accurate in this type of circuit than a voltmeter. If that 12 volts shows up, the relay is the likely suspect.

As a further test, or if you don't have a helper, use a small jumper wire to connect 12 volts to that smaller terminal with the red / light blue wire. That should make the relay engage.

If you don't get 12 volts on the red / light blue wire when the ignition switch is in "crank", its adjustment and the clutch switch become the better suspects. Let me know what you find, then we'll figure out where to go next.

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