My M715 has both 24v and 12volt. The 12 volt operates the lights, heater blower fan and small fuel pump. The 12 volt alternator is a GM unit from the late 70's/early 1980's.

Here is what I have. When I take a voltage reading off the battery without the truck running or any 12 volt accessory on, I get about 12.4 volts. When I start the truck and turn on the fuel pump, I get about 12.1 volts. Then when I put the headlights on/turn signal lights on, I get a reading of about 11.7 volts.

The reason I ask is because after a month or two, it seems the 12 volt battery goes weak/dead. The battery is about 3-4 years old and charges up well if I trickle charge it overnight.

My buddy had an extra GM alternator and I switched that in and I still get the same readings, so that rules out the alternator. It should be noted that there is one heavy red/hot going to the stud on the back of the alternator. There is also a red and white wire going into a small white plastic clip in the top of the alternator. The red wire coming out of the clip is also attached to the hot red/alternator stud on the back. The white wire is just clipped off and is hanging there.

Any ideas? I thought that the alternator would "charge" the battery while running any give me a higher reading on my voltmeter, but it goes down instead. I also do not have a voltage regulator of any sort that I see inside the engine compartment.

Just scratching my head at this point...