Alrighty y’all I’ve got a 95 12v 5 speed after about 30 minutes of driving my check engine light comes on and my voltage meter drops too the low side truck drives as normal and starts super easy I’m going to check my alternator today and battery but I was thinking maybe the grid heater was coming on anyone have any ideas?

I would have the alternator tested. I drove from Amarillo Tx to South Fork Co with a dead alternator and couldn’t tell except for scan gauge going to sleep.

Probably alternator 

27 minutes ago, Dieselfuture said:

Probably alternator 

X 2

Yup I agree with alternator check. Verify the blue wire for 12V at the field leads.