1987 F150 - With the help of this forum I corrected the problem of no lights. I changed all of the fusable links at the starter relay with in line buss fuses and all of the electrical is working.

A new major problem has now started. The alternator fuse keeps blowing out. I replaced the alternator yesterday with an original 65 amp alternator but that did not help. I replaced the 15 amp fuse with a 20 amp fuse and it still blew. The battery is not charging.

The problem is where the one wire from the relay goes to three wires to the alternator. The fusable like showed 14 amps.

When I replaced the fusable links I soldered all of the connections so they are strong.

What could It be? Should I be using a larger fuse?

 

Solved my own problem - I thin. The first advice I received from one of the local auto shops was to replace the fusable links with the buss fuses. In going to another store another salesperson mentioned that I had to replace the alternator link with a 14 guage not a 14 amp fusable link because of the amount of current going through.\

I will do that this afternoon. Now I am wondering about the rest of the fuses I put in. Are they too high or too low?

Does anyone know what the relationship is between the fuses and the wire size on:

20 guage
16 guage
14 guage.

 

Don't know the relationship. And I think it's more a question of the characteristics of the fuse vs the fusible link. The automotive electrical system involves a lot of surges, and a fusible link can handle these better than a regular fuse. I would keep going up on the fuse rating on the alternator till it quits blowing. But once in awhile the alternator may be called for full output, which is may cause a regular fuse to blow.

My old cars don't have any type of fuse in the alternator/underhood wiring. And I have read most of the car manufacturers are getting away from fusible links, and are going to what they call a "maxi" fuse. These can be rated up to 100 amps.

 

A chart from the National Elertic Code:

COPPER CONDUCTOR AMPACITIES, IN FREE AIR AT 30 DEGREES C
================================================== ======
INSULATION RUW, T THW, THWN FEP, FEPB
TYPE: TW RUH THHN, XHHW
================================================== ======
Size Current Rating Current Rating Current Rating
AWG @ 60 degrees C @ 75 degrees C @ 90 degrees C
================================================== ======
20 -------- *9 ----------------------------- *12.5
18 -------- *13 ------------------------------ 18
16 -------- *18 ------------------------------ 24
14 --------- 25 ------------- 30 ------------- 35
12 --------- 30 ------------- 35 ------------- 40
10 --------- 40 ------------- 50 ------------- 55
8 ---------- 60 ------------- 70 ------------- 80
6 ---------- 80 ------------- 95 ------------ 105
4 --------- 105 ------------ 125 ------------ 140
2 --------- 140 ------------ 170 ------------ 190
1 --------- 165 ------------ 195 ------------ 220
1/0 ------- 195 ------------ 230 ------------ 260
2/0 ------- 225 ------------ 265 ------------ 300
3/0 ------- 260 ------------ 310 ------------ 350
4/0 ------- 300 ------------ 360 ------------ 405




* = estimated values; normally, these small wire sizes
are not manufactured with these insulation types

 

I have never read anywhere that the amp capability of a wire from the NEC chart has anything to do with the rating of a fusible link. The ratings in the above chart are how many amps a certain size wire can carry with a tolerable temperature rise. I would think a fusible link would be rated as to when it was getting ready to burn in two.

 

I don;t know what your short is, but I do have two important things. Never use a larger fuse than what is recommended (though it will locate your short pretty quick by melting the wiring and possibly causing a fire) and never solder fusible links. It changes their ratings, pretty much making them like using a larger fuse.

 

Actually, your table as you have made it here is written as though the ampacity of the wire increases with temperature rise, which is incorrect. Ambient temperatures above 86F require derating of the wires current carring capability, not increasing their current carrying capabilities. Using the 14 gauge as a example the maximum current that is reccomended to be run on that gauge wire would be 25A for the unrated insulation that is used on all of the aftermarket automotive wiring. In addition to the loss of current carrying capabilities that are associated with the rise in temperature, you also need to keep in mind the length of the run of each wire as this also will determine the wire size that is nessasary. These things are important to keep in mind to avoid wiring problems and possible fires.