need help with gen 2. light not on but still charging.

[lonewolf90]

On my 1986 m1008 my gen 2 light is not coming on when I turn the key on but when i start the truck in goes in the green like everything is working fine. So I been on here trying to find something and have come up empty handed. So here is what I got. Key off there is 24.9 volts at the red with orange wire on the top post of alt. The red/w wire 12.5 volts. At the 2 plug connection The black/yellow wire is 12.5 volts and red wire 24.9. Thanks for any help.

Key on not started
Red with orange 24.9
Red/w 12.4
Two plug connection
Black/yellow 12.6
Red 24.9

Truck running
Red with orange 29.3
Red/w 14.6
Two plug connection
Black/yellow 29.3
Red 29.3

Back battery pos is 29.3 and neg is 14.6

 

[rlltide12]

2 possibilities. Either 1. the bulb in the dash is blown or 2. (Most likely problem) the connection for the bulb holder on the printed circuit is dirty and is not making connection. To correct either issue, pull the gauge bezel, then you will be able to pull the white dash gauge housing out of its holder. Lot easier to do without the dash pad in the way. Also tricky is getting the speedometer cable and molded connector loose. Once out, take all the bulb holders out of their sockets and use a pencil eraser to gently polish all the copper tabs on the printed circuit. Then take a piece of sand paper and polish all the brass tabs on the bulb holders. Good time to replace all bulbs while you are at it. Then you reassemble and have no more bulb issues. I ran into the same problem.