Daihatsu Rocky intermittent won't crank

I have a '92 Daihatsu Rocky that sometimes won't crank. When the engine/environment is cool, it will consistently crank, but not if it's hot. When it won't start, jumpstarting makes no difference (it's not the battery or the alternator not charging the batter). When it won't crank, bumpstarting will start it immediately.

When the starter does crank, it starts immediately and runs fine. 

This trucklet couldn't be much simpler, so this has to be a solveable problem.

What I've done:

1) bypassed starter switch with push-button start

2) bypassed clutch safety switch

3) new starter (new Bosch, not rebuilt)

I'm at the point where I'm just going to rewire the whole starter system.  

However, I thought of one more thing.  Maybe a bad ground between engine and chassis/negative battery terminal?

Any other ideas?

Sounds like resistance is increasing with heat.  Either in the starter itself or in the wiring/connections. 

Check all grounds and connections including at the battery itself. 

jfryjfry said:

 

Check all grounds and connections including at the battery itself. 

 

 

This is what I was going to suggest. It sounds like a connection isn't quite right. It could be something actually in the wiring harness- I had a car that would start great when it was hot, but not when it was cold. One of the wires in the harness was spliced badly, and I didn't find it until I removed some electrical tape.