The timing light could care less where it gets its power from. You can pull another car, truck, lawn mower, tractor, up next to the truck and hook the timing light power leads to it. As long as the pick up lead is in line with the #1 plug wire on the truck you will read the timing on the 4400. 🛠

Martin
'62 Chevy C-10 Stepside Shortbed (Restomod in progress)
'47 Chevy 3100 5 Window (long term project)
‘65 Chevy Biscayne (Emily)
‘39 Dodge Business Coupe (Clarence)
“I fought the law and the law won" now I are a retired one!
Support those brave men/women who stand the "Thin Blue Line"! Hug a cop!
USAF 1965-1969 Weather Observation Tech (I got paid to look at the clouds)