Occasional starting difficulty with Digital HP CD box in my D200

I think I figured it out... I started thinking about grounding and after looking around I didn't see any ground straps going from the cab to the frame. I assume the factory relied on the cab mount bolts for electrical grounding. Well mine have some good surface rust being 50+ years old so I figured adding a ground couldn't hurt. I added a wire going from the engine to the firewall and the voltage to the ON wire for the ignition box went up a decent amount, it's now about 9.8V during cranking. Still seems to be some voltage drop through the ignition switch but I haven't had any starting issues since.