Car: 1987 Corvette Coupe
Alternator: 105 amp

Ok I have almost exhausted my ideas for why Fusible Link C keeps blowing on my charging sytem. This is the fusible link in-line between the 10 gauge wire on the alternator to the jumpstart junction block behind the battery which itself is a (+) connection right off the battery.

The very last thing I found tonight before coming inside is that I am getting continuity between ground and the jumpstart junction block. I am pretty sure this isn't right at all. :nonod:

Things so far gone wrong and/or found.

1. Finished installing engine and systems.
2. Charging system was fine.
3. Went for test drive and 3 miles out the entire electical system shutdown for about 1/2 second and came back. From this point on the charging system was failed.
3a. As always expect dead alternator, install new one. Still nothing.
4. Inspection showed Fusible Link C blown.
5. Continuity on cables was fine, no shorts found.
6. Installed new 30 Amp fusible link. Continuity checks out.
7. Start car, fusible link blows immediately.
8. Jump junction block and alternator momentarily to test, charging system works.
9. Search for things wrong.
10. Starter connections extremely loose.
11. Tighten starter connections firmly, suspect loose connections creating extreme high current draw.
12. Install 30 amp circuit breaker (i'm not going to keep doing those damn links!)
13. Start car, still no dice. Charges.... stops.... charges.... stops..... so the breaker is opening and closing.
14. Inspect for more.
15. Find continuity between ground and jumpstart junction block stud where all terminals are connected. Damnit.

I'm out of ideas. It looks like I'm going to have to search for pinched wires aren't I? There is a ground strap above the oil filter that I am not sure is routed right. Does this one go to the frame?

Below is the wiring diagram (its huge sorry, wanted to make SURE you could read it). Perhaps I do not have the correct fusible link? I am using a 30 amp. The alternator lead is 10 gauge wire, the other side of the original fisible link was the what appeared to be 12 gauge.




[Modified by scorp508, 11:20 PM 10/3/2002]


[Modified by scorp508, 11:26 PM 10/3/2002]

 

There could be an internal short in the alternator.

 

Whoops sorry, check out 3a added above.

 

Are there any grounds accidentally connected to the + lug on the jumper block?

 

Mine is an 88, automatic. There are two ground strap to the engine block, one with a ~12 guage wire and the other is the negative cable. At the bottom left bell housing there are three ground strap to it, one of them looks like a flat braded metal wire going from the side of the car near the body, I didn't check where it goes. I think there was another ground attached to the upper left bell housin stud/bolt. Did you ground those wires?

 

Scorp,
The 30amp circuit breaker might not be heavy enough. The alternator could be putting more that 30 amps through that line. Try hooking up a battery charger on the battery, turn it on to 35+ amps, and then start the car and see if it is pulsing the 30amp circuit braker. I've seen guys using circuit breakers before in the alt output, they were usually 60amp. The 30amp might be enough with the bat. charger on, but I think it is to lite. :cheers:

 

On my bellhousing....

Upper Left Bolt : Tach Filter Mount
Upper Right Bolt : Nothing
Middle Left Bolt : Wiring Harness Bracket
Middle Right Bolt : Wiring Harness Bracket
Lower Left Bolt : Nothing
Lowe Right Bolt : Nothing

That ground strap you mentioned is located on my engine as one of the 4 connections to the large bolt that goes into the block above the oil temp sending unit and oil filter.

 

Scorp,
Another thought, do you have an old amp gauge lying around in your collection of goodies? If you do, put it in line in place of your circuit breaker and see what it reads when you start car. If it pegs the gauge, you have something pinched or crossed that is causing the alt to full field charge. Make sure that you have the correct amount of voltage coming out of alt when it is running, if it is too high it would also indicate full field charging of alternator. It could be possible that with the loose starter wires it spiked the alt. and caused damage internally that is now causing the full field condition. I'll keep thinking, good luck. :cheers:

 

Wow, I don’t know where to start.

Did you isolate the suspect circuit? By this I mean did you disconnect the battery and disconnect the plug to the alternator and then check for continuity? (Suspect wire with fusible link to ground)



[Modified by Bender, 12:27 AM 10/4/2002]

 

Yes. Full continuity from alternator to jumpstart junction.

Also, both red leads on alternator show 12v hot at all times as they should.

 

Look at page 6D5-2 (88 shop manual, hope your is the same) the lower left bell housing bolt does has some ground attach to it.

 

Scorp,
I'VE GOT IT, I KNOW WHAT IS WRONG CAUSING THE CONTINUITY AND PULSING OF THE CIRCUIT BREAKER. YOU TELL US WHAT YOU BUILT FOR AN ENGINE, BE SPECIFIC INCLUDE ANY AND ALL POWER ADDERS, AND THEN I'LL TELL YA! :lol: :lol: :lol: :lol:

just kiddin! :cheers:

 

Let me try this again.

1. Disconnect battery
2. Disconnect alternator
3. Disconnect starter solenoid
4. Check for ohm reading from fusible link connection to ground.

You should not get any reading in step 4. If you do, you have a short and can backtrack. When checking step 4, make sure to wiggle wires around.

Hope this is clearer.

 

Ok, can do that, thanks. When you say the fusible link connection I assume you mean the end that would normally connect to the alternator.

 

That would work. You are drawing to much power causing the link to blow. I am assuming you are grounding out. With this test, you would isolate the circuit and you shouldn’t even get 1 ohm of resistance.

 

I guess we should also somehow decide if 30A is enough. Anyone know what a "3 Rust" fusible link means to GM?

 

Scorp- I know this is probably not of much help- but if you've got continuity at hot "to ground", there's your short- follow it back. (?) When your alt thows out charge, it blows the link, circuit breaker.... I had a similar problem with my other car- harness problem- that blew fuses only when the car was started and charging from the alternator kicked in, otherwise the short was so minor (low current draw) that it didn't drain enough current to pop the fuse- start her up and...pop- sounds like the same prob here. I'd follow your hot lead down to your starter and see if it's grounding out.... Just a thought.-J

 

I have no idea what a “3 Rust” fusible link means.

One more thing that I want to add that may or may not be related to your problem. One time many years ago, I changed a motor in a car. Everything worked fine, but every morning the battery was dead. It was driving me crazy. (Way back then, my father was still alive) My father walked in the garage when I was trying to figure out the problem after several days of dead batteries. He looked at it and started to laugh at me. He told me that I forgot to ground the engine to the frame. I thought he was crazy, but put on two ground straps. Now, this was in the old days where the battery was grounded directly to the motor and the radiator support. After I put the additional ground straps on, no more dead battery. Ever since then, I ground everything out very well.

 

The "3" means the metric wire size is 3.0 mm^2. That corresponds to 12 AWG. That's how they label wires in schematics, I assume fusible links are the same.

Rust should be the color of the wire or fusible link.

The third entry is a circuit/node number. e.g. ".5 BRN 25" means 0.5 mm^2 wire size, brown wire, node 25.

 

It won't matter which end your check from.

The question is is the block grounded; if so which lead is causing it.