Think about what needs to happen. 1. Large cable from battery to solenoid needs to be clean and tight on both ends. 2. Starter needs to be well grounded. 3. Trip wire to solenoid needs to have sufficient current to close solenoid contacts. 4. solenoid contacts need to be in good enough shape to allow current to flow. 5. Battery needs to be charged with clean connections.

It should go without saying that the starter itself needs to work and the engine needs to be free to spin.

On Dodge Cummins solenoid contacts wear out. I saw a place on line that sold generic contacts for pennies. There is a guy that sells them for $35 because others aren't willing to do the work to find what fits.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.