QuestionVan, I reinstalled the passenger side alternator this morning. Everything is ok,for now. The fuse block had a fuse blown in it. It was the one that says 24v on it on the bottom of the block. Whats this do? If it was blown could it overload the electrical system? The alternators were tested and are putting out 13.4 volts on the driver side and 12.7 on the passenger. Is this ok? Should they be putting out more? The guy who rebuilt the alternator needed a voltage regulator and another set of brushes. He said they were fried. Can the alternators get 24 volts to them somehow? The wire I was referring to was on the passenger side firewall that looks like a battery cable. There are five or six of them bolted to the block there. I disconnected the one that ran that jumper plug. I tested the on to the starter and it reads 27.6 volts with the key on. Most of them were exactly the same reading. Thanks for the help.
AnswerHi Nate,
That pair of blocks on the passengers side is where all the 24 volt things are connected.
The batteries connect to both...one is positive, and the other is ground.
Then the slave cables, starter solenoid, rear mounted radio connections for the military radios, glow plug resistor if it is used on that truck, etc. The passengers side alternator output also connects there.
They should all test the same, since it is a metal strip with multiple studs from each one.
The alternators should put out 14.5 volts and about 100 amps on his test stand.
The passengers side alternator, if you are measuring from the engine block or frame ground, to the Batt stud on the alternator, will show 24 volts...or actually, whatever reading you get if you measure from the grounded battery neg terminal, to the rear battery pos terminal.
That passengers side alternator, though, does NOT ground to the engine or body on the neg post of the alternator. That post connects to 12 volts.
That 24 volt fuse feeds the volt meter, and supplies the exciter power to alternator #2. There is a relay under the dash for the volt meter, and when it is closed by the ignition switch, the 24 volts goes to the meter. It also goes thru the Gen 2 indicator light in the dash, and thru the firewall to the passengers side alternator small plastic two pronged plug. That's to keep the meter from continuously measuring voltage, and pulling the batteries down.
The little two prong plug on the alternators is for exciter power, and for charge measurement.
They do NOT get the exciter power from the same place.
Lets start with the drivers side alternator. The Large red wire, from the + or Batt terminal, goes to the diamond shaped black plastic connector stud on the firewall. The small red wire in that two wire plug, which is # 2 if you can find that, goes to that same diamond shaped connector. In other words, you could use a little jumper from the + stud on the alternator, directly to that little #2 plug. That measures the output for the regulator.
The -, or Neg post of that alternator connects directly to the engine block ground.
Now, go to the passengers side alternator.
The large red wire from the +, or Batt stud, goes to that multiple stud junction block on the passengers side of the firewall, behind the batteries. That is 24 volts.
The small red wire in the two wire connector at that alternator, #2 in that plug, goes to the same terminal block as the output from that alternator. Likewise, a jumper wire from that alternators + terminal, to that #2 connector, would work just fine. measured from there to the engine ground, it will show 24 Volts.
Now, if you measure from that #2 plug, to the Neg stud of THAT alternator, it will show 12 volts. Sounds confusing, right? That Neg terminal does NOT connect to engine ground. The wire from that stud....red with a white stripe.. goes to that diamond shaped 12 volt stud on the firewall.
Although both alternators are 12 volt, and completely interchangable, the one mounted on the passengers side is inserted into the wiring system, and actually starts grounded between the batteries, and only charges the rear battery.
The drivers side alternator only charges the front battery.
That other wire on those small plugs...the #1 terminals....goes thru the firewall, and to the Gen 1, and Gen 2 lights.
If those bulbs are burnt out, their respective alternator won't charge, or may take a long time to begin charging.
That is where the excitation comes from.
So if that 24 volt fuse is blown, the passengers side alternator may not charge at all.
Probably the worst thing that could happen, is for someone to connect the passengers side Neg stud, to the engine block ground. That would make that 12 volt alternator try to live with 24 volts connected to it.
Nuff for today?
Van
PS....I have the wiring diagram directly out of the military manual right here in front of me.
