Yes, the lift switch energizes an electromagnet in the solenoid that causes it to move to the "closed" position (with an audible click). That closed position completes a direct circuit from the battery to the lift motor that allows it to run to power the lift pump.
The amount of current the motor draws is VERY large, and a solenoid is a kind of heavy-duty switch that can handle that current.
If you're not hearing the click, then either the solenoid is bad, or, it is not getting current from the switch, which is my guess since you've replaced the solenoid. You could have a broken wire or bad contact from the lift switch to the solenoid. This would be the wiring in the trailer.
Here is a link to the 1990 Model Year Owner's Manual for HiLos.
https://www.hilotrailerforum.com/f49...-classic-2016/
HiLo publishes a "generic" manual for all trailers each model year and there are very little changes from year to year. Your trailer should be very, very similar. There is a wiring diagram in it on page 18.
The lift circuit is in the upper diagram and it shows a yellow wire from the lift switch to the solenoid that would supply activating current. With a voltmeter, you could check this wire at the solenoid to see if it has battery power with the switch in the lift position. In the diagram, it shows 4 wires to this solenoid post. The lift switch wire, the positive battery cable, the charging wire from the circuit breaker in the tongue, and the connection to the solenoid switch (which may be internal and not visible). The negative post on the solenoid has the negative battery cable and a wire from the lowering valve.
I don't know how to tell you to identify these posts, but the alternator shop should be able to do it.
I really suspect your problem is in the trailer wiring.
- Jack