Just run a dedicated ground wire from the heater to a known good ground or directly to the negative battery post.
Your firewall is probably not properly grounded to the frame/battery, etc.
Install good ground straps from the battery to the cab and frame and clean up both ends of the one that's already there. The standard Chevy ground setup is barely adequate in the best of conditions.
Last edited by Otto Skorzeny; 09/17/2022 12:07 PM.
