Always a good idea to add extra ground cables to major parts...include the block, head, transmission,alt...even extra battery to frame cable......this eliminates thin layer corrosion related voltage drops....quick,easy and cheap.....this fix has solved many tail chasing electrical issues...make everything going to the negative post... one big, fat,low resistance, happy conductor....no one can say (probably a bad ground).....

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1978 Yellow 300D (The Mustard Toad)
1980 Blue 240D (The Iron Toad)
1989 Grey Mitsu.4WD Mighty Max Pickup (Needs a Diesel transplant bad)

(Open the pod bay doors HAL)