Charging trouble.

[Runslikeapenguin]

So i had my room mates 1979 620 all squared away for him to use as a daily driver, up until yesterday.

 

I get a call from him at like midnight after he got off of work. He says that his lights wont work, his radio wont work, all the dash lights came on and he pulled off of the freeway and shut the truck off and it wont start. So i grilled him until i got the truth, which was he left his lights on at work for like 9 hours, then had some one jump him and they hooked up the jumper cables backwards on his truck and ran it for a second (so he claims) then they fixed the cables jumped the truck and he took off. Well he had melted some wiring and god know's what else and was running on what was left of the battery for like 5 minutes.

 

So i went out to the gas station he was parked at and fixed the wiring and put my multimeter on his battery, it was at 8v and when i jumped his truck nothing worked except the engine. So i went and got a new battery at Wal-mart put it in and got him home.

 

I started working on it today and i pulled the Alt and had it tested, Autozone said it was bad and i got another. I installed the new alt and still I'm only reading 12.35 at the battery posts with the car running.

 

Wiring fixed, new alt, new battery.

 

what else could have been fried that I'm missing? Is there an external regulator on this beast or is it internally regulated? Is there a relay or something i should be checking?

[drxfter]

I had a look at my 620 an my trusty manual: it shows an external voltage regulator is mounted remote of the alternator, so it would seem likely that this, along with other components, is fried. It should be a black box bolted on the inner guard next to the battery.Also check all of the fuses and fusible links, as an incorrectly jumped battery is the fastest way to blow every major fuse on the truck. Be thankful that it actually runs, too! ;)

[banzai510(hainz)]

a 679 should have a IR alternator. The reg is inside the alternator.

How about measure at the output post of the alternator for voltage.??try that if you get say 13.5 or so I say alternator is good and you have dirty or high resistance connections soemwhere.

You clean the insde of the battery cables???????? Mine were dirty and you have a big voltage loose between the batter post and cable. used those battery post cleaners(wire brush).

 

 

You know autozone and others sell shitty alternators!!!!!!!!2/3 out of 5 could be bad from the box.

 

 

ck all your fuses everything

I dont know later model 620s but ck

 

 

also soemthing could be loading down or shorted.

 

let truck sit and if doesnt start in a couple days you have a short to ground for sure.

[Runslikeapenguin]

Strangely none of the main fuses blew in the truck. Which is what has me worried, that means i lost wiring somewhere instead of the fuses.

 

I checked the charging from the alt posts as well as the battery and it was slightly less than the battery. Meaning the power i was seeing at the alt came from the battery. The thought of a bad alt from the factory did cross my mind, i would rather not take it off again but i could have it checked. The good news was removing the alt in this car was pretty easy, which made me happy.

 

 

I'm not sure what the charge light did when my friend did all this but it doesn't come on at all now. It should turn on with the key then shut off as soon as the truck is running right?

[datsunaholic]

Could have blown the choke relay, its hooked up to the alternator sense wiring. Or could have just blown the bulb it it suddenly found itself with 24V running through it.

[Runslikeapenguin]

I was curious about those three relays that were behind the black cover. Which is which? and how would i check them?

[ppeters914]

If it -REALLY- has an external VR, now's a great time to convert to an IR alt.

 

Your room mate owes you -BIG- time for being a moron. Tell him next time to call you first before getting "help" from other idjits.