I have a 98 Ram 1500 with 318 V8 and 2 wheel drive.
When I try to start it all I get is a single click.
Since I had a battery that had been giving me some slow starts I replaced the battery and cables. Try to start, all I get is a single click.
Next thought isit must be the starter so I replaced that and all I still get is a single click.
Now I'm lost, what could it be? Everything else electrical seems to be working fine except this.

 

The main power cable to the starter motor is two pieces. One from the battery to the PDC, and the other from the PDC to the starter. Verify that you have 12 volts at the fat cable on the starter.

Welcome to DF!

 

What is the PDC?

 

Power Distribution Center. Big black box behind battery with fuses in it.

 

Gets plenty of power. All other electrical works, new cable recently replaced.

 

Maybe the ground wire isn't getting a good connection to the frame.

 

There are several grounds- battery to block, battery to frame, frame to chasis. I would check all of them also.

 

Good point gdstock!

 

Unless you got a bum starter (always a possibilty, but kinda remote), maybe try this: measure the resistance between the negative battery terminal and the case of the starter. It should be practically zero. (This is pretty much the equivalent of saying "make sure that the negative battery cable is well grounded at the block, and the block is grounded to the frame").

As everybody has said, it's probably a bad ground somewhere; you might have enough of a ground that "everything else works" as you said, but not good enough to handle a big load like the starter motor. Just enough of a ground to let the starter solenoid make a pathetic attempt at doing something.