Alternator Excite Wiring Issue

[DmitriM1028]

Hi, I have a 1985 M1028 6.2L. I'm having a problem with ALT 1. The light on the dash came on the other day and I tightened the belt, replaced the relay, checked all my fuses. Everything was ok.. except on the alternator excite wire, the white/brown wire on the plug only has 2.8V with engine running or just key on, and the alternator is not charging. So I took my power probe and gave it 12V from the Battery and it started charging but only to 13.3 V and the alternator got hot. When I unplug the white plug and check voltage I have 12V but plugged in it drops to 2.8V. From what I've read in other threads this leads me to believe the alternator needs to be rebuilt? So I ordered kits for both of them. My question is why does it only have 2.8 V plugged in and why does it start to somewhat charge when I jump 12 V to it? I don't Have a wiring diagram yet for the excite system. I'm assuming the alternator is shorted out inside and causing voltage drop, but how come it doesn't blow the fuse or something else. I'm currently waiting for the rebuild kits now, but I need to understand why the voltage is doing that and why when I jump it directly it starts to charge a little bit more. I'm confused. Thank you so much. I'm having a small problem with ALT.2 Also, the light on the dash is blinking on and off when revved up or driven so I cleaned the corrosion off the printed circuit board and replaced the bulb, relay, and tighted belt, still doing it. That's why I ordered 2 kits and I ordered new belts. Am I missing something else. On my fuse panel all the lettering has worn off so I don't know exactly which fuse is which I have to check them all when I have an issue. Does anyone have a diagram of that panel. Is there a manual I can buy with all the diagrams for the whole truck? Thank you for your help, sorry about the long story, just trying to explain everything good. I'm new on this site. Thanks again.

 

[WWRD99]

Hi, I have a 1985 M1028 6.2L. I'm having a problem with ALT 1. The light on the dash came on the other day and I tightened the belt, replaced the relay, checked all my fuses. Everything was ok.. except on the alternator excite wire, the white/brown wire on the plug only has 2.8V with engine running or just key on, and the alternator is not charging. So I took my power probe and gave it 12V from the Battery and it started charging but only to 13.3 V and the alternator got hot. When I unplug the white plug and check voltage I have 12V but plugged in it drops to 2.8V. From what I've read in other threads this leads me to believe the alternator needs to be rebuilt? So I ordered kits for both of them. My question is why does it only have 2.8 V plugged in and why does it start to somewhat charge when I jump 12 V to it? I don't Have a wiring diagram yet for the excite system. I'm assuming the alternator is shorted out inside and causing voltage drop, but how come it doesn't blow the fuse or something else. I'm currently waiting for the rebuild kits now, but I need to understand why the voltage is doing that and why when I jump it directly it starts to charge a little bit more. I'm confused. Thank you so much. I'm having a small problem with ALT.2 Also, the light on the dash is blinking on and off when revved up or driven so I cleaned the corrosion off the printed circuit board and replaced the bulb, relay, and tighted belt, still doing it. That's why I ordered 2 kits and I ordered new belts. Am I missing something else. On my fuse panel all the lettering has worn off so I don't know exactly which fuse is which I have to check them all when I have an issue. Does anyone have a diagram of that panel. Is there a manual I can buy with all the diagrams for the whole truck? Thank you for your help, sorry about the long story, just trying to explain everything good. I'm new on this site. Thanks again.

The relay is for alternator 2. The gen 1 light has to turn on with the key...off when running. From what I read it is coming on while driving. Unplug the 2 pin connector and test for power with the key on....not plugged in. Should have battery voltage. If you do then rebuild the alternator. Can do both since youre in there.

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