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fuse- link blowing

4K views 2 replies 2 participants last post by  Mr Mac 
#1 ·
I've been having trouble with my 1990 F-150.

It started with a fuse-link blowing. I believe it was fuse link P (that's the designation in my "electrical and vacuum troubleshooting" book) when that happened the truck died.

Next, My mechanic changed the fuse-link out with a Napa fuse link of the same gauge. The truck ran for a few weeks (it's not a daily driver so I used it maybe 4 of 5 times) then that fuse-link tried to blow, but didn't, and fried my under dash wiring harness. The main power wire (yellow) to the ignition switch melted and burned a bunch of other wires. I was finally able to replace the harness, and put the truck back together.

I changed out the alternator thinking that that might be the cause of the trouble. I put an in-line fuse (20A) in place of the fuse-link, and ran the truck for a few more weeks, then pop! the fuse blew.

I have looked for a cause but cannot find one. Dose anyone here have any idea what could be causing this problem?

-everettdale
 
#3 ·
Sorry, been away for a couple of days.

You mention the P link. In my manuals I see the M link which connects to the voltage regulator so I believe you are on the right track. If your truck has the regulator in the alternator then that is the most likely cause otherwise look for the external regulator.

Mac
 
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