How do i replace the solenoid only?

Check the starter solenoid and the connections from the battery to ground, battery to fusebox, ignition key switch, neutral or park safety starting switch, solenoid, and solenoid to starter. Make sure you have ignition key switch wires connected to the solenoid - without them - the solenoid can not close to send 12V to the starter.

Replace the starter. It's not a coil, it's the solenoid. You can't get it without the starter.

No. the solenoid has a plunger that hooks onto the arm that pushes the pinion into the ring gear just before the starter motor starts to spin. There is an adjustment at the pivot that has to be set for the new solenoid

Seems your solenoid is activated or jammed. If the solenoid is part of(mounted on) the starter, it's a bad starter. Take the small ignition (starter) wire from your solenoid, it should only be hot (have power ) in the start position. The starter shouldn't turn with it removed. BobB

Check your connetions and make sure you have the wires correctly positioned on the solenoid.

were you trying to start it before you removed the other battery?
if so the solenoid is stuck.
turn the key on and hook up the battery and let it start then turn the key off and let it die. the kick of it starting should knock the solenoid back like it should be. if it keeps trying to start you will have to pull the starter and replace the solenoid

Most starters now a days have the solenoid integrated into the starter and are therefore irremovable. Replace the whole starter.

this sounds like you have a problem with the starter solenoid contacts in the solenoid.change the starter motor as it comes with the solenoid and the starter sometimes goes bad afterwards.or you can buy just the solenoid and replace it alone.

Buying a solenoid without a starter is the same as buying a hamburger without the bun. The solenoid sits on top of the starter in a GM and they come out and go in as a pair. If you go in to buy a new starter it should have a new solenoid already on it. Replacing one without the other pretty much guarantees that you will be doing this job again a few months down the road for the part you didn't do this time. Hope this helps.

no u must remove the starter, as far as the reason i suspect they did something wrong or used sub standard solenoid repair parts