Somewhere here on SS I posted up about the resistance values and how the circuits work of the FSOV. The one pictured in the first post is a Trombetta, they were VERY problematic. They were changed to the Synchrostart brand and things were much better. The biggest issues on the C and B for that matter, were grounds. One of the fixes was to eliminate the harness ground and ground the FSOV wire coming out of the solenoid itself, directly to a bolt on the intake manifold, however, when that is done ALL of the grounds must be checked to make sure there is a good return path back to the batteries.
The books stated that anything less than 10 ohms of resistance was a "good" ground, nope. If you have 10 ohms cold, guaranteed the value will go +20 when things heat up or when things all start working at the same time. They need to be in the area of 1 ohm. Check engine to cab and chassis, cab and chassis to battery ground. When these were new, we saw a mess of them, most were just the FSOV being the Trombetta. Replaced it and all was good. But these things are pushing 40 years old and have been through many people, places and processes, who knows how the connections are now. For all anyone knows, the ground straps were removed and never put back in place orput on loose and painted over.
If good grounds cannot be achieved through cleaning and tightening of cables, you can make new ground paths using 8-10 ga wire from and to any cleaned/prepped point on the engine, cab, chassis. IIRC, we had to run new return path wiring on the early, 1991-93 Navistar COE trucks that JB hunt ran because the grounds were junk in the Navistar harnesses.
The ground R values apply to the control box grounds too.
