Hi, My 99 F150 Has started to blow the #21 start fuse under the dash. But, only sometimes. It can go up to 15 starts sometimes and then turn the key to start and I hear the fuse pop. I unplugged the pigtail wire from the solenoid to isolate it and then jumped with a screwdriver for a while and finally popped another fuse so I figure the problem is after the ignition switch but before the solenoid. My neighbor laughs every time I start it up with the screwdriver. Wait 'till he has trouble... Has anybody had this problem or know what it could be???

Any help is appreciated. Thanks

 

Circuit depends on whether a manual or automatic.

If manual, goes to clutch pedal switch, then to starter relay.

If automatic, it goes to the clutch switch jumper (same harness is used in that portion of vehicle), then to the TR sensor on the transmission, then to the starter relay.

Steve

 

This is the Automatic diagram from the 2000 EVTM ( only one I have access to at the moment ), so it should be close ( same ) , but if something does not look correct, don't panic that something was changed on your truck ( at least on the surface ). Some of the late build date '99s follow the 00+ almost to a T, but there are some items that are not the same.



You unplugged the circuit 1093 from the Starter motor Relay, and the fuse still blows, even though you are shorting hte pins on the start motor relay ?

Did I get that correct ?

Does not make sense on the surface why that would happen, if you are not using that circuit, for starting. Is it actually upon starting, or at the time of moving the gear shift lever from P to D ?

 

I got the fuse to blow via the Ignition Key even after disconnecting the small wire from the solenoid. It took a couple of tries but finally blew. "Sorry for the confusion in my original post". It has no pattern. Sometimes the fuse will blow twice in a row and then not again for a over 10 starts. It is 5.4 auto trans super cab 4x4. Thanks for the help guys. It is appreciated.
Thanks Again

 

P.S. Fuse will only blow when ignition key is turned to the start position. No problem in run position. Thanks

 

That fuse controls the power to the starter motor relay so it will only blow in the start position when it has power. How could it blow if that circuit is off? What wire did you disconnect? What terminals did you connect to jump the starter?

JMC

 

I disconnected the small push on wire from the starter relay/solenoid. While disconnected, the fuse still blows when the key is turned to the start position. 12v power is being supplied from the ignition switch in the start position via the the red/lt blue wire.(confirmed 12v in start position via test light, with fuse removed.) That's why I believe the problem is after the ignition swtch but before the solenoid. Wire shorting out? Neutral safety switch on trans shorting out?

Any help is appreciated. Thanks

 

It has to be for that fues to blow. There is a short to ground after the fuse. Unplug the DTR sensor plug and probe the Dark blue w/ orange striped wire for a short to ground. Then the tan w/ red striped wire for a short to ground. There is a black wire that is the ground. If it has rubbed any of these two wires and made contact it could cause the fuse to blow. Check the wire loom for any sighs of melting or chafing. An intermitant short to ground in the switch will cause the fuse to blow when the starter is engaged.

JMC

 

Thanks. I will check those wires. I hope I can find the problem. I just don't look forward to cutting a big loom of wires apart to find the short but, I'll do it if I have to.

Thanks again for the help...