[Fish out of water]

Can't get cart to run (was running fine) with 4 ga wires all tight
I checked F&R switch and micro switches and speed control micro with parts from a cart that works
even pulled the motor to bench test it, it works fine
I didn't check solenoid cause my brother said it tested fine
when I put the meter on the big posts of solenoid it reads 16v when I check the working cart it shows around 38v ???? why the differnce
1) have I missed something
2) don't trust my brother
3) is the solenoid my problem

Thank you in advance
Matt