1982 c-1500 diesel V8 pick-up won't start.

I have the above truck stored in my shop. I took the double batteries out to do some cleaning of the supports and the batteries. The batteries are fully charged but now I can't get any electrical to the starter switch and can't start the engine.

What is the best way to handle this. Is there a step-by-step to track the problem down?
Could I start it bypassing the starter to get it running and out of the shop and to a mechanic I'm asking to check it over?

Appreciate your help.

Just to let anyone interested.

I finally got the truck going. It needed two new batteries.

Thanks