Charging issues.

[buffblazer]

Put a new alt on the 86 k5. and my batt light was on, tested the alt and it's not charging. Took it in and had it tested and it passed.

What's my issue? It's just a 2 wire alt. Everything was hooked up right.

Also the old alt was replaced due to a bent shaft not a charging issue

 

[496truck]

Then they tested it wrong or something.

It charged with the old alt. Doesn't charge with the new one. Try again, with another alt.

 

[buffblazer]

Got another alt still won't charge. Idiot light will be real faint when idling but bright when reved up

 

[buffblazer]

It will slowly charge up to 12 volts but the idiot lights stay on. If I turn on my lights and offroad lights it drains the battery in like 5 mins with it running.

It's s cheapo 65 amp alt ( I know I know but its all I could afford)

Is it possible that it's just not strong enough? Or do I have other issues?

 

[diesel4me]

Assuming you have a typical 10SI GM altenator as that year should have---



You must have 12V at both of the small wires on the plug that goes in the altenator with it running,test it with a test lamp or voltmeter...12V should also be present at the large stud at the back the big red wire goes on also...(always with key on or not)..if that wire is dead,it might be cut,grounded from being melted to the engine,or more likely,the fusible link in it has failed,sometimes they dont burn out completely and will let a limited amount of current pass thru it,which will cause trouble ..)

One of the two smaller wires in the small plug is hot only when the key is on,its usually a white wire..the other ,a brown or tan one ,is hot all the time...

I bet no current is going to the white wire,or not enough,that is what energizes the feild coil in the altenator and makes it start charging,sometimes when you go to touch the test lamp to that wire you'll hear it kick in and the engine slow down a bit..or the fusible links at the starter have been fried or half fried,there are 2 of them in the red wires ,those power the fuse box and everything under the hood,there might be another one near the power brake booster also...

It would be rare to get two defective altenators in a row,especially if both do the same thing...its probably a bad wire or fusible link,or bad grounds ..

 

[buffblazer]

So I'm an idiot, I wired up an amp gauge with an in line fuse a long time ago.

It blew, idk why but it did.

Back to the basics always check your fuses...

 

[ChrisPerry]

How big is the fuse? With a 65amp alt it should be a 100amp fuse maybe even a 120. Personally I would ditch the amp gauge and put in a volt meter. I don't like the charging wire entering the cab, I had a bad experience. Too small of a charging wire + mechanical oil pressure gauge = small flame thrower. 'Nuff said.

 

[diesel4me]

I had a 72 K5 that had a factory amp meter in the dash cluster--it never moved,so I assumed it wasn't charging,but testing voltage with it running proved it was (13.8V),so I started thinking about taking the dash out and replacing the gauge--but first, I looked at a Haynes manual that had a wiring diagram,and it showed 2 fuses in the wiring harness ,one on each side of the front fenders next to the headlamps--had to remove the battery to find the one on the passenger side..both were glass fuses,and both were blown...replacing them after cleaning a ton of green corrosion out of the holders (that were rubber ,and looked just like the ones at the license plate lamps where the wires join the tail light harness),I again had a working amp meter...I never would have guessed GM put TWO fuses in such a strange location for the amp meter!..

Speaking of oil pressure gauges and fires--I remember the night I took a girl out in my '69 GTO,hoping to impress her--and her toes found the oil pressure gauge nylon tube I had going to the triple gauge cluster under the dash--I felt a warm liquid on my sock,then it felt HOT--and soon I heard her sqealing,the oil line came out of the ferrule and was shooting hot oil ALL over both of us!.....spent half an hour trying to stop the leak,I couldn't re-use the crushed ferrule,so in desparation I used a bic lighter to melt it closed,so we could go home!..so much for ever seeing HER again!..her dress looked like a spotted leapord,she was PISSED!...my car was a stinky oily mess too,the interior was never quite the same after that episode--now I refuse to use that nylon crap,only copper tubing on my oil gauges!...but I also had an amplifier power wire rub against a copper oil pressure line and ground out on another vehicle,and I almost lost the car ,it took me a good 2 minutes to get the battery cable off!...had to crimp the copper tube shut to get home..

 

[Fordum]

I don't like the charging wire entering the cab, I had a bad experience.

While most automotive amp gauges require you to run the main power into the cab, there is no reason you should have to.
Electronic and power amp gauges are often remote sensing. You simply put a shunt of a known resistance in the circuit, say .01 ohms, and put a voltmeter across it.
The voltage drop is the amps.
For that shunt, 10 amps equals .1volts, and 100 amps equals 1 volt.

With a sensitive meter, you can use a length of the main power wire as the shunt.

Alternators are correctly rated in watts, but you seldom see that rating.
I once saw a neat crossing needle gauge for that.
One side was volts, the other side was amps, and the center scale where they crossed was watts.

Never found out where it came from, probably be easy to find these days with all the search capabilities.