connection meltdown at end of fusible link

[str12-340]

So here is a head scratcher. After driving my 70 Dart for a week at a car event including 200 miles to get there, I'm riding along and the ammeter goes to 60 amps charge, the voltmeter reads 16 volts and I switch the car off and run to open the hood. I check a bunch of connections and wiring and the only thing amiss is that the connector from the main hot wire to the fusible link is melted together in a major way, but the link seems just fine. I restart the car and limp it home 200 miles. and the only symptoms from my obsessive gauge watching is that whenever the engine slows down to less than 1500 rpm the voltmeter and ammeter bounce around like bowl of jello - over 1500 gives 12.5 volts and a bit of a charge with rock steady needles. Any guesses as I tackle this? The front wiring harness is only a few years old (repop from year one with no previous issues). What really creeps me out is that the connector was fried but the fusible link never burnt...

 

[67Dart273]

What probably happened is that something went wrong causing over-voltage and THAT caused the visible damage to the link and connector

Part of the PRESENT problem is probably that connector is now damaged, and not reliably making connection.

Most likely causes of the start of it are probably "lost ground" to the voltage regulator or something wrong internally in the alternator. The green connected brush (field) going to ground, a bad rotor in the alternator. "Something" that would cause a bad overcharge condition

 

[moparman007]

It does for sure sound like a lost ground or short causing a dead ground.

 

[str12-340]

I'm searching for the source of a brief dead ground and and appreciate the leads, But why didn't the fusible link burn and protect the system???

 

[67Dart273]

Fuse links are not dependable. My example was just a guess "could have happened" Here's a true story...........

In the very early 70's not long after I bought my 70RR two girls in a Datsun A-holed the thing in National City (S. of San Diego).......... While it was in the body shop (a long story in itself) they gave me a beater of a loaner, a /6 Valiant.

One morning it was chilly at the RADAR shop, I was getting off work, so I fired it up and went back into the shop for a few minutes. Our leading chief, who I SWEAR was the pattern for "Detective Columbo," came in, knitted his eyebrows, "I just have one little question? Is is supposed to be squealling and smokiing?"

So I go out and the alternator has FROZE and the "loose" fan belt is smoking around and around the pulley!!!!

I shut the thing off, loosened the adjuster, and moved it with a rag. I don't know why, I just did. When I moved it, the DIODE which had fallen out and down INSIDE SHORTED, and I got to sit there and watch the engine bay harness go phzzzzzffff.....ssssss...phzzzzzuuussssaaaawwwiiii......zzzzzziiiiiii.........zzzzziiiii....iiiittttt!!!!!!!

AND THEN THE FUSE LINK BLEW!!!!

So I called the dealer

"Send out a wrecker for this wreck of a loaner, and send out another loaner."

So of course the dealer sent the "jumper cable guy" with his beater, a trunk full of junk batteries and and a few pair of booster cables.

He opens the hood and says "THIS thing is all burned up!!!!"

So then HE goes in and uses the phone, and says, "send out a wrecker and another loaner car!!!!"

 

[67Dart273]

So far as your problem, I would get up under the dash, and examine what all you can see and smell, and do the same under the hood. Look carefully for melted, damaged wiring. The example I used "fit" with a voltage regulator going nuts or coming ungrounded, causing a severe overcharge condition.

I would scrape the VR mounting clean and remount using star lock washers

When you are "ready" to fire it up again, do this...............

Leave the battery unconnected. Repair the link. Then put a test lamp in series from the battery post to the ground cable. If it lights, go around make sure EVERYTHING is off, including trunk, hood, glove box, and dome lights. And the radio if it works with the key off. You should have NO glow at the test lamp

If that is OK, go ahead and touch the battery cable. It might produce a SMALL spark ONCE.

If that is OK, hook up the cable loose. Check stuff like accessories on the key, dome light, headlights, stop lights, etc.

Next pull the field wires off the alternator and lay them safely aside. Start the car and run, and check that out.

Next hook the field wires back up. Start and run WHILE MONITORING the battery voltage with a meter. Slowly bring up RPM. If battery voltage goes above 15--16V find out WHY. If it goes up to maybe 14.5--15, that is OK "for now" Check out if it charges, headlights, heater, etc etc.

 

[str12-340]

Thanks 67Dart273! I'll be ferreting this out going slowly and will post when I get it figured out. I'm lucky to have a local electrical diagnosis and rebuild place that has been going since the 60s so I can have their old pro run the alternator and voltage regulator on a stand and find any internal issues, but I will follow your steps if those check out well...