Help with starter and solenoid

[Dbluff]

SS- I ran into a problem with the starter solenoid and now maybe starter…

For a little bit on button start truck would click and not fire up, on and off, no real big deal.

Then while driving I heard a humming noise and then a pop and all electronics went out.

So I checked batteries and one was bubbling out fluid. I figured my solenoid had probably welded shut and grounded out.

I removed bubbling battery, and simply put pos and neg on remaining battery to test, and a big spark when connected pos.

so I disconnected wires on starter solenoid , touched battery again and no spark.

fast forward, I ordered a new solenoid, new battery, installed all, check connections on battery, no spark , so I’m thinking great solved problem.

put everything back together, turned ok 3 way, power seems normal, I hear fuel pump. Go hit starter button, and big sparks off connection between batteries where pos and neg cross to make 24v, melted half of the post on battery.

could it be my starter was compromised also?

any further test I can do for starter?