Hey all, After a 6 hour job of replacing the heater core over the weekend, I was reinstalling the battery as the last step and made a dumb mistake of connecting the ground cable first, then the positive. When wrenching in the positive cable on the battery, I grounded out on the alternator and sparks flew. Wrnech was on the positive battery terminal and went right to the body of the alternator. I finished everything up and she started right up but only had about 10 volts in the system. Drove it up the street and had a few test done to it. Fusible link from battery to alternator showed no break. Bought a new alternator, same issue no change. I did a little research on the forum and found a wiring diagram for the charging system. So trying to solve this issue, is there a fuse the charging system goes through? I would imagine the fusible link to the starter is fine because the truck turns over fine and I imagine it has no affect on the charging system. Really stumped on this one. all other devices in the vehicle work fine. even the intrument panel and it is showing the voltage at 10 when the truck is running which was verified with a meter. Another BTW, I hooked the meter to the positive stud on the back of the alternator and the positive battery terminal and I had connectivity which is how I determined the fusible link between the battery and alternator was fine. .

 

IN my haste, I failed to mentioned, vehicle info 96 blazer. Any help is greatly appreciated as I'm out a vehicle until this is corrected.

 

That sounds like a fairly lucky way to do it, all the shorted power would have gone through the wrench, and ground wires, not your positive distribution. Look at the battery ground wire, where it attaches to the vehicle. Also there must be some sort of ground strap to the engine, but I don't recall seeing one. Thats more likely with everything else working fine.

A quick check of mine, with no problems, shows 11 ohms from battery terminal to alternator chassis, and that sounds reasonable to me, lower is better.

 

Tested all fuse links and all were good. Is it correct to test the alternator by place one meter lead on positive stud of the alternator and the other to ground? Also could I have potentially not hooked something back up right when I put the dash back and reconnected the dash wiring harness the would affect the charging system? Everything else seems fine. Charging system worked fine prior. Also. I read somewhere else in another thread here that the battery light in the dash was out it would be an open circuit and cause problems. Thoughts?

 

Ok both alternators just passed the local auto store test. So what would not allow the alternator's to charge. The other plug in the back of the alternator, what is it? It only has one wire and I assumed it was for the instrument panel gauge. Does the ecm control the charging system? What tells the alternator to put out juice?

 

I also have a brand new battery. Showed 11.8 volts after sitting all day from a near drain. I'll check the negative ohm read to chassis when I get home.

 

Max was 3ohms but settled down at less.

 

is your instrument panel batt light on when you turn key on?

If not replace the bulb. Should fix it

And 3 ohms is too much resistance in any power lead. Should be less than 1. Check your probes {short blk and rd tips together}

Look close.. is there a decimal point?

 

The alternator chassis can be corroded, you can scratch it a little to make good contact. Or wire brush a small spot. Inside where it's actually electrically grounded should still be clean.

You want to go by the lowest stable reading. Make sure it's not saying K-ohms or M-ohms.

The plug on the back should be related to the regulator built into the alternator... but I don't have the diagrams right now to see where it goes. If you can get over 14V by measuring the stud to chassis voltage when it's running, thats not your problem.

 

It was 0.3 ohms. Whenfirst connected then dropped after so I think that's good. Hoping the idea with the instrument cluster light is it. I couldn't remember if the batt light came on and I've got the alternator out of the vehicle and the battery until this evening. I do remember being surprised that not all bulbs/sockets were present in the cluster when I took it out. I even took one of the bulbs out to look at it and then put it back. Not sure if it was the batt light or not