So we been messing with alternator problems the past few weeks as my other posts show. We thought it might be a relay and many other things but found something out today. Ahhh where to begin??? Ok....the wires on the alternator. We have 2 wires going into the plug on the alternator. One red one tan/white. With the ignition on all the wires have power. Ignition off....Red has power but the tan/white is dead. I understand this is normal? The main bolt on wire has power and is good also. All fusible links are tested and good. BTW...the problem started when the fusible link burned out that runs to the alternator. We put an inline fuse to trouble shoot. With all accessories on....the fuse blows and volt meter in the dash drops from 13 to 8. It makes sense being that the alternator isnt getting power anymore. So after replacing the fuse about 4 times we checked things and tried again. This time the fuse blew out and after putting in a new fuse the alternator still wont produce power. All the wires are still getting 12 volts to the alternator in the run position.

So after days of scratching heads and searching posts on here. We tried jumping the "S" and "F" plug inputs on the alternator straight to the battery. It worked then! The alternator was putting out 14.5 volts.

Question is....what could be causing the problem? Is there a way to rewire the alternator to maybe bypass the factory setup? I dont want to blow out the alternator regulator or anything. The car btw is a 89 RS 5.0 TBi. Its my nephews and hes borrowing one of our cars for now and we need to get him back in his car.

 

like the main output wire on the back of the alternator, the red wire in the plug has full time power. the other wire in the plug has power in the run position.
if you put a small inline fuse (under 50 amps) on the main wire, it will blow the fuse at idle.
if i were going to use a fuse for testing purposes, i wouldn't use one in the main wire of less than 80 amps.
even at 80 amps, with a good alternator and heavy electrical load the fuse can blow a little above idle.

 

The fuse we put in isnt on the main bolt on red wire. Its on the red wire in the plug. There use to be a fusible link there but to avoid having to change blown links everytime it popped....we put in a fuse. The fuse isnt blowing out anymore and its getting 12 volts to the alternator plug but still no charge. I put a jumper wire on the "F" prong (plug unplugged completely) and the alternator charged good. I also tried jumping the wire across the "F" and "S" prong.....still put out a charge. I then put the jumper wire on the "S" prong only and nothing? Why does it charge with the red wire (on the plug "S") not working? Should the alternator charge with only the tan/white ("F" wire on the plug) hooked up?
I tried running a wire from the ign source on the fuse box straight to the tan/white wire on the plug and it didnt charge. It showed 12 volts though??? Why would it be charging with a jumper wire directly to the alternator and not when its to a ign switched source??

 

with the key in the run position, all 3 wires should have battery voltage on them.
with the key off, only the tan/white wire should NOT have power.
the S terminal is the voltage sensing input to the alternator.
you can run the red wire on terminal S to the main red wire on the back of the alternator, that is how most people do it when they upgrade an older car to the later style alternator. when i swapped my TPI motor into my car, i made the same change.
the tan/white wire splits off and 1 side goes to the coolant fan relay and the other goes to connector C207 and turns into a brown wire, then goes to the fuse box to the fuel pump/fan 20 amp fuse.

if it charges when you have all 3 connections on the alternator jumpered to the battery, it should charge with the wiring plugged into the alternator.
if it doesn't charge, then 1 or more wires isn't supplying the proper amount of power to the alternator. a poor connection somewhere can show battery voltage with a volt meter when its unplugged to what it supplies power to.
with everything hooked up, turn the key on and check voltage at each connector.

 

Thanks Denn.... The info on the tan/white wire is very informative. Thats one of the questions Ive been trying to get answered for a week lol. I actually found the problem last night though. It was a bad connector plug on the alternator. The "F" prong wasnt making a connection to the plug. I noticed that the "F" prong in the alternator was a very skinny prong. After looking at the plug awhile....I kept thinking to myself....this plug connector looks a little big to fit good on that little prong. So I took it in the house and played with it awhile. I used a sewing needle and pried the connector inside the plug a little tighter. Went out....plugged it in and hooked up the wires............and bam 14.5 volts ... Now I just have to figure out what made the fusible link blow out in the first place. If there was a short in say the horn....if I took the horn fuse out would that stop it from shorting out???? Its the only thing or way I can think of finding out what the problem is without physically tracing every wire in the car. Thanks again.....your awesome ;P

 

no problem

unlike a regular fuse, it takes a fair amount of current to kill a fuse link, it could have been just its age.
for the link to burn out, the problem would almost have to be between the link and fuse box. the wire between the link and what it suppliers power to may have insulation that has been rubbed thru and causing a short is a possibility.


another one of the things i did on my car when i did the TPI swap was to move all the fuse links from the starter up to the battery.
i use a dual terminal battery in my car and use the side terminals to supply the main power to the starter and ground to the motor.
i use the top positive terminal to supply power to the fuse links and the output from the alternator.
i use the top ground terminal as a redundant body ground.
i did it so if/when one of the links burn out, i can patch it fairly easily on the side of the road.
the down side to moving them like i did, it changes what happens if the positive cable has a bad connection at the battery or starter. you can still have a nice solid click from the starter relay and all the other electrical things work fine, but it won't turn over because the starter doesn't get proper power from the battery thru the main cable. it acts just like a bad starter, and its bit me a couple of times.