[demian5]

Take a set of battery cables and do this:

Hook one end to the engine block, the other end to the frame.
For the other cable, connect one end to the body and the other to the frame or engine block.

If this helps, you have a ground problem where the existing ground isn't enough. Should be:
Cable between battery and engine (alternator bracket, water pump bolt, or bolt on front of block by fuel pump)
Cable between battery and vehicle body (inner fender usually)
Cable between engine and vehicle body (firewall and valve cover bolt usually)
Cable between engine and chassis (valve cover bolt and frame)
Cable between chassis and vehicle body (under cab)