I have an 1989 dodge truck cummins diesel . the power just went out no headlights no nothing , if i turn the key over the starter relay makes a click . I replaced the relay an it has a new battery an voltage regulator , if I hook a jumper cable to the positve terminal an touch the starter it will start but no electric works , does anyone know what this could be

Ignition fuse, or you have a bad ground on the iginition system.

If the batteries are out? I would get a multi meter of your price range. On ohms scale you can measure resistance to see if you have a circuit ( cct) from one point to another point. On DC scale you can measure voltage from point to point. Check fuse links connections maybe bad? contacts not making? etc. A good multi meter of your price range is a good place to start. Goood luck.