I am looking for some troubleshooting help with my 88 F250 4x4 manual trans.
I am having a problem with the starting circuit. I can start the truck by jumping the starter solenoid with a screwdriver but not with the key switch. I have an idea that either the key switch or the clutch switch may be defective, but I'm not sure how to test them. I am only getting 7v to the solenoid when testing with my meter. any help on this would be greatly appreciated.

 

i would have to say it,s the ignition switch because i doubt it would even start by jumping across the solenoid if the clutch switch was bad ! your talking about where you have to push the clutch in before it will start ? you can test the clutch switch by unplugging it and hook the 2 wires together and see if it will start by the key ! if it,s still the same then hook the wires back up on the clutch switch and replace the ignition switch !

 

When you jump the circuit across the solenoid you are bypassing the clutch and ignition switch. It the same as hooking battery positive directly to the starter. It tells you the battery cables are good, and the starter itself is ok.

The purpose of the solenoid, actually a relay, is to allow a small amount of amps to control a large amount of amps.

On the side of the solenoid there are one, or two, small wires with boots. If there is only one, that wire sends current to the solenoid from the ignition switch through the clutch switch and to the solenoid.

If there are two wires, it is the one marked "S" on the solenoid.

To test the ignition switch and clutch switch remove the small wire from the solenoid and attach a test light from the female end of the small wire to ground. You can also use a multimeter set at 20 volts DC.

Now get in the truck press the clutch pedal to the floor, and turn the ignition key to the start position.

The light should come on, or battery voltage should indicate at least 12.6 volts. If there are two small wires attached to the solenoid make sure you are testing the right one. Agian it is the one marked "S" on the solenoid.

If the light does come on it means the solenoid is bad. But, before you change it make sure the old one is properly grounded. Run a wire from the where it attaches to the body of the truck to battery negative, hook the small "S" wire up, and try it again.

If the light does not come on bypass the clutch switch, as discribed in a previous post, and try again.

If the light now comes on the clutch switch is bad.

If the light does not come on with the clutch switch bypassed it means the ignition switch is bad, or as with all these test procedures, there is a bad wire, or connection.

 

Thank you very much (bandit1948 & thexlo8ers) for taking time to help. I will check out the switches & try to determine if one or the other is bad.