new to diesel world and need help
 

i have a 1992 w350 flat bed 1st gen but having some problems in the charging system it stays charged with battery hooked up but un hook the battery and it dies i think it the altenator but want to make sure before i go and spend money on something it does not need also battery voltage say its 12 when running but whe go to start t it will crank once and the click runs fine as long as i dont shut it off

Run down to the local garage and have them put a "load test" on it, they will tell you if the alternator is bad in 2 seconds.

ok newest find i must have a wiring gremlin every time i turn head lights on or turn signal the voltage gauge follows the turnsignal could this be a bad relay switch