Good news, alternator has not gone south after all....

[Nickathome]

I decided this afternoon to find out once and for all what the hell was wrong with my truck's alternator. I started by checking the connections on the unit. My truck has an alternator out of an M151, and it also has the two wire retrofit connection, as opposed to the other system with the generator, etc. There is a thick wire that goes to the starter, and a thinner wire that goes inside the truck and into the spider harness on the instrument panel. Anyway, all was Ok under the hood, so I decided to trace the wiring through the firewall and under the dash. As soon as I traced the thinner wire, I noticed it was unplugged from the spider harness. My truck has the rubber connectors in this area, not the older metal ones, and when I was installing my heater, I had taken out the instrument panel in order to see what I was doing under the dash. I must've jarred the wire connection loose without knowing I had done it. The wire was numbered 27, and as soon as I reconnected them, and hit the master switch, I realized that I had solved the problem. I started the truck and let it run for about 15 minutes, the needle of the volt meter was in the green again and moved slightly when I'd rev the truck. I even tried the system under load, by turning on the lights, wipers heater etc, the needle barely moved. I'm happy this problem was such an easy fix and my alternator was not the cause of the isuue.

[rixm37]

That has got to feel great!!! It's amazing how alot of the time it is something really simple but hard to figure out that causes a problem.

[WarrenD]

That's good news. I have a habit of doing similar things, my 4 year old snowblower's engine seized last year (with over 12" snow already down!) and after removing the rear cover, I got the crank to turn again (big socket+long bar!). After I got things back together, it would start, but not run for more than a few seconds, seeming to need continuous priming. After several hours of consternation, I found that a choke/vacuum linkage rod was just slightly bent, I had done it in order to take the rear cover off and forgot during re-assembly. Stuff happens, glad it was an easy fix.

[Nickathome]

Yeah, I'm hoping that was the cause. I was wondering last night though why the one wire not being connected would cause the alt not to charge the batteries....I'm hoping my elation doesn't turn sour. I did charge the batteries last week and am hoping my seeing bright lights etc, isn't just the freshly charged batteries I'm seeing. I guess the only real way to know is to put the volt meter to it while the truck is running.......We'll see for sure soon. I'm going to take the truck out tomorrow to get fuel and to take it on a short run. I'll run the heater and the lights just like durin gthe storm to see if it drains the batts. If no noticeable drain, then I guess I'm good to go.

[WarrenD]

Best of my recollection, the alt needs 12 volts fed to it to work (talking 12V system, so in this case, 24V). If the wire that was disconnected had something to do with that circuit, it would make sense, especially if everything was working correctly before. OTOH, it may have been grounding out, in which case the draw would be substantial.

[MSeriesRebuild]

That was definitely your problem. There are 2 wires, the smaller of the 2 feeds power to the alternator when the ignition is turned on. Thus it connects to wire 27 which powers up the instrument panel when ignition is on. Power through the small lead simply turns on the unit. The larger gauge wire is the lead that flows current to charge the batteries. Long story short, having the small lead unplugged yields the same result as having your radio unplugged. Unplug the radio, get NO music, unplug the alternator, get NO charge.

[Nickathome]

Thanks for the info fellas.

[k8icu]

Yeah what Charles said.

[HingsingM37]

Glad to hear it was an easy fix