Trim solenoidelectrical problem

ok- we bought a new/used boat

ok- we bought a new/used boat july 5th. First day we took it out -no problems. 2nd time we took it out-our trim went out. After a lot of troubleshooting-we found it was the solenoids-they BOTH went out at the same time. So we replaced them. By the way- we checked all electrical associated with the trim--The trim up/down and trailer button on the throttle arm and four wires all the way back to the solenoids. The all tested good. I examined the wire all the way back-it was like new. I tested the plug from those wires and the plug at the solenoid-and everything was fine. We tested the pump itself and it works fine up and down. So after everything was fine we replaced the solenoids and we had trim/tilt working again. So we took the boat out on Sunday and everything worked fine. We went tubing and swimming for about 5-6 hours then when we decided to go in and trailer the boat--the trim didn't work anymore! Both solenoids went out again. There is no limit switch attached to it--the only wiring attached is what I described. Someone eliminated the limit switch. After examining everything I could I found that by the lower unit-The trim sender wires are frayed/stripped and exposed. BUT-the trim sender is in no way connected to the trim itself. The trim sender just goes to the gauge. So-is there anyone that maybe had a problem like this before or has any ideas for me? I can't just go blow $50 to replace solenoids every time we take the boat out. I appreciate any help.
thank you
tom

"Have you jumped across the ne

"Have you jumped across the new solenoids' studs to see if they will turn on the pump? If they turn the pump on then the trouble is in the trim/trailer solenoid control circuit. Apply 12 volts to the small + wire of each solenoid. If they turn on the pump then look into the switch circuit. If not then they are dead. But why?

Have you checked the 120 amp fuse for corrosion? It is on one end of the solenoid buss bar and the connections should be shiney. It can be disassembled, polished w/fine steel wool or emery cloth and put back together tight.

If the solenoids are dead, open them up by bending the tabs on the bottom and removing the nuts from studs. Take a look at the contactor disks; if they are blackened and have arc weld burns on them the pump motor is probably drawing too much current. Either the motor is worn out or the wrong solenoids were installed."

"OR the battery cable connecti

"OR the battery cable connections are corroded,especially the neg one ."