1988 ford f150


#1

just bought this truck. it had this problem when i bought it. new alternator new battery new starter. alternator not charging. bypassed fusible link with wire. alternator seems to work ok 13.89 volts. however put a regular in line fuse like under the dash upto 30 amps. blows everytime?

i have never had a vehicle with fusible link. i went to my local carquest said i could ot get a replacement and had to do it this way? Do it need to use a different type of fuse? I dont know why fuses are blowing? I do not have a good wire layout to run down the problems?

any ideas? thanks for the help


#2

The fuses are blowing because you have a short to ground.
Troubleshooting this type of problem usually requires a schematic, a wiring diagram, and some understanding of electrical circuits. What I’d recommend up-front is
(1) remove that bypass wire and put in a fusible link. Buy a few while you’re at the parts store so you can troubleshoot without causing a fire. You might even use alligator clips on the ends to make putting new links in while you’re troubleshooting,
(2) remove that 30 amp line fuse,
(3) remove the fuses for every circuit that’s noncritical to engine operation,
(4) see if the problem, goes away.

If you’re lucky, this will help you at least isolate the problem to the noncritical circuits… or eliminate them as suspects. The most common places for shorts to ground are where the wiring harnesses go through the cutouts in the body metal. The most common of all are the ones where the harnesses travel from the body into the doors. That portion of the harness gets flexed big time every time the door is opened or closed. Those fuses will be for the power doorlocks and the power windows. If the problem disappears with those fuses removed, you’ll need to remove the inner door panels and the kickpanels, cut the harness open, and visually inspect the harness wiring insulation, splicing and reinsulating any that are suspect.

You might be able to get a wiring diagram, a schematic, and even “exploded view drawings” for the door panel and kickpanel installations from the dealer… because of the age you might have to look for an old repair manual on the internet. These things will be an enormous help.


#3

I’m in the dark about the 30 amp fuse and exactly what it does but I agree with mountainbike that fuse needs to come out and be replaced with a fusible link. It could be that a short has been created because of someone eliminating that link.
Are you saying this fuse is between the alternator and battery?

You could temporarily install say a 20 amp circuit breaker in place of the fuse. That would overheat and open the circuit but at least would keep you from buying fusible links until it’s sorted out.

The charging schematic is pretty simple on these vehicles although I can’t remember it off the top of my head. I’ve got a number of Ford schematics so I’ll take a look-see and be back…

For what it’s worth, all cars have been equipped with fusible links of some sort for many decades.


#4

thanks for the help. i have a chiltons manual for the truck however it only has partial diagrams that are kindof cut and paste because of year and drive train. really hard for me to use.

i am looking for a good complete diagram. there are only fusible links in the engine bay only fuses in the cab. will start with your advise first thing in the morning. thanks again.


#5

My schematics all show a pretty common arrangement; 4 or 5 fusible links off of the starter solenoid depending upon model and engine, etc.

You might consider going to the AutoZone website and starting an account there. There is a repair section with chassis electrical and wiring diagrams. Odds are very high that on a common vehicle like an '88 150 there will be a diagram.


#6

If the link was in the main charging lead, then 30 amps is probably not enough. Most alternators can put out 50-70 amps…I bet your 30 amp fuse is blowing right after the engine starts and the alternator puts out a big surge. Most auto-parts stores will have replacement links rated up to 100 amps…


#7

Autozone has the same diagrams I have.

Carquest had no idea what I was talking about. Can I buy it buy the foot?


#8

Yep.

You can’t substitute a fuse for a fusible link.

A fuse is a fast blowing device. Which means it burns up if the current exceeds its rating.

A fusible link is a slow blowing device. Which means it can handle inrush current for a period of time without burning up.

Tester


#9

Yes, Dorman offers a 10’ roll of 12 gauge fuse link wire. I would use 2 strands in parallel to handle the full alternator load…You can also replace the link with a heavy fuse…Bussman has those up to 100 amps…about $3.50 each…

Think about this…it’s 5 below zero and the old Ford takes a bit of cranking to get it started…The battery is somewhat depleted. The truck finally starts, you turn on the headlights and heater…At that moment, the main charging lead out of the alternator will be carrying close to the alternators maximum output, 50,60, 70 amps, something like that…So you need to wire that circuit accordingly…