won't start sometimes

[fordcowgirl]

the truck is a 97 f350 auto. 4x4. about every other time you go to start it, it just clicks like it has dead batteries but it has new batteries, alt. and starter. if you just touch the jumper cables to the post it will start but we have cleaned the batt. post also.

[vitalidle]

Put a volt meter on the battery posts. Neg to neg Pos to pos turn the motor over and see if you get a voltage drop and what it is reading You might have some resistence in the circiut with bad cables or connections on the starter.