JD 4010 24v starter + series/parallel relay issues, cont'd

Hello again all,

The patient: 4010 w. Delco 24v starter, 2 x 12v batteries + Delco alternator, using a Delco-style series/parallel relay. Had been starting fine until I had the bright idea to replace harness. Then starter barely turned- apparently receiving 12v only. Everything checked out, wired to spec, batt's good, etc. Start problem apparently resolved by running small (10ga) jumper from Bat B + to starter ground terminal. No idea why this worked- but P.O. had a pencil sketch illustrating setup so I followed it. But then, after a week working fine, it stopped starting again. Relay energizes fine, but fuse on + jumper fries instantly when batteries connected.

Suspicion went to starter solenoid. Sure enough, on disassembly solenoid contact plate had clearly welded to contacts at some point, so not releasing. Ordered new solenoid & replaced. Fuse still blows, starter doesn't spin. VOM shows:
12v at batteries
24v at series/parallel relay when starter key turned. Relay energizes as it should
24v at starter solenoid (trigger posts) when key turned
24v at starter battery terminals when key turned

Still, starter either doesn't spin, or barely spins. Was spinning fine last week.

Any ideas/recommendations not already offered??

Thanks!

Without knowing exactly how it's wired one will just be guessing the correct way to solve this 24 volt system. Are you aware that the 24 volt system is capable of catching on fire without the addition of large circuit breakers? Does this tractor have these large circuit breakers?

If I was repairing this 4010 I'd change it to a 12 volt system & solve a lot of future problems