[mr48chev]

Check the voltage at the battery as Dsraven said first. It might not hurt to put the charger on it for a bit while you check the rest of the connections. A multi meter is you best friend here. after you check the voltage across the top of the battery connect the ground lead to the engine on something bare metal and see if you get a full voltage reading. Then see if you get full voltage at the terminal on the end of the ground cable. I've seen too many that had several coats of engine paint working as insulation to keep the cable from making a good ground. BARE Shiny metal. If the cable is fastened to a bracket rather than the block you need bare metal contact spots all the way back to the block to make sure you have good electrical flow.

I've gotten to where I upgrade the cable size on 12 V rigs after fighting with my 77 dualie They like a good amp flow that those skinny cables restrict.