Fuse-able link keeps burning on firewall

[Cornfield creations]

I had this problem a long time ago when I put a different alternator on. Now again since I upgraded to a cs-144, 140 amps. When the a/c is on and windstar fans running, stereo on, and outside lights on, it shoots up to 18 volts. Normally without a/c and fans, it's sitting at about 15-16.

Now I did put resistors in the sensing wire and that did the trick, but why would it randomly shoot up that high? Bad regulator in the alt?

I got it home knowing the link burned off, but when I got in the driveway, it would surge between 12-17, up and down, up and down. Just seems odd like something went out in the alt.

 

[diesel4me]

It could be whatever is shorting out causes the altenator to charge all the more,and that burns the link up--the altenator dont know if the load is a battery or a dead short,all it knows is something is demanding more current,and when it supplies it,the wiring cant handle the overload...

You need to do some investigating to find out if anything is shorting out first--use the old bulb between the battery terminal and cable trick to find a drain on it..if no shorts are found ,then I'd assume your accessories draw so much current the higher power altenator can keep up or exceed the demand,but the wiring is too small a gauge to handle the amperage...did you run a thicker wire from the altenatoi stud right to the battery??..the stock 10 or 12 ga. wires aren't up to the task of handling 100+ amps especially after they get old and may have corrosion building up inside them..

 

[63chevyll]

Sounds weird, but I had same problem after I installed 2 very large amps, and multiple speakers in a blazer I owned. Couple of 12s, 4 mids, and 4 tweets.

I installed a bigger alt(essentially from a 94 suburban) and kept blowing firewall link at junction block.

I had all factory grounds and in good shape, but what finally ended the blowing links was new 4 guage grounds from body to frame, frame to engine, and engine to body, and another ground at the rear from body to frame where the amps were.

Don't know if that's your problem, but I chased that Damn problem for a while. The same issue even blew out an autometer tack.

It's like the factory grounds are only adequate enough for factory loads

 

[Cornfield creations]

Yeah it originally destroyed my fact. tach, twice. When I went back to a factory size alt. 60 amp. It quit. I know I have a 4 gauge ground from the battery to the body. May try running them to the frame and block.

The fuseable link is 16 gauge which I think is tiny for what power goes through there, but I stuck a 10 gauge piece of wire on there to get it back into the garage and it fried that too. The alt. should only supply the draw needed to maintain the voltage level. I may test the battery, it's an optima but I put it in there in 2005, so it may have lost capacity and therefore charging more to make up for it.

 

[Fordum]

If the voltage regulator is doing its job, and it has a good ground reference, then it will maintain approx. 14.5 volts no matter what up to the limit of the wattage output of the alt. Some have temperature compensation built in that will change the output voltage depending on the air temps.

Under certain circumstances, a defective battery can cause high voltages, but usually it will not crank if its that bad.

In a straight resistance setup, the higher the voltage, the higher the current, so if the voltage goes up, so does the amps.
But, if you are frying a 10 gauge wire with a load that a 16 gauge wire should handle, then you have a major short somewhere.

Or a major open. Its possible that another, heavier, cable is not making good contact, and its load is going through that link.

Which link is blowing?

 

[Cornfield creations]

It's the wire going from the block next to the booster, and runs down to the 2 wires that goto the starter.

 

[diesel4me]

Make sure that junction block thing itself hasn't melted and allowed the shunt inside to ground out on the firewall....something is probably shorting out and creating a heavy drain on the battery...a friend had multiple fusible link failures on his K5 and it took him a long time to find out what was causing it--on his truck he found out the power tailgate motor was not shutting off after the window went up all the way!--one day it stopped working and he smelled burnt motor windings...and the fuse never blew on it either!..after he put another motor in the tailgate it didn't melt fusible links any more...might have been a poot ground issue??..