Hi I am new to the forum. I have a Hilo 2001 22 foot trailer.
I bought the trailer locally at the end of May. I re-laminated the wall by the shower that had been damaged by an ice dam.
When I got the trailer home it would only go up with jumper cables attached to the battery.
For 2 months this summer we used the trailer on 110 volt service including lights, pump, AC, tanks and battery gage etc.

I bought a new deep cycle battery and new battery terminals, since one was cracked.
Now I must have a short somewhere. I read 12.9volts at the battery and at the closest battery lead bimetal breaker to the solenoid. I also read 5-6 volts at the small activating terminal on the lift solenoid and read 5-6 volts on the down stream terminal on the solenoid as well as on numerous spots inside the trailer.

The 110 volt system works and the inverter has the green light on.

With the master switch in one position we get some light from the light outside of the door and one inside light that looks to be a low watt night light. No other 12 volt systems work.

I am no expert at electronics. I have a standard circuit tester as well as telephone line tracer. I hope it it the main 3 way switch.

Comments welcome. Thanks Marty.

The only other thing I took note of was that the AC switch was turned between AC and Heat. These 2 options are side by side on the AC roof unit.

This response is far from a comprehensive answer. I have a 2000 22ft Towlite that may be similar to your trailer.

1) Clean and/or check the connection where the ground wire connects to the frame. Mine was horribly corroded when I bought my trailer in 2018. Until you are sure of the Negative Battery terminal to frame connection is good, make voltage measurements with the black meter lead on the negative battery terminal.

2) Check that your breakaway switch is open. The steel cable that connects to your tow vehicle goes to this switch & closes the switch if the cable is pulled.

Good luck

Marty, welcome to the forum. Your comments tell me you have a faulty (poor) electrical connection somewhere in the trailer and as On The Road said, it could well be a corroded ground wire, attaching to the frame. You DO NOT have a "short" - that is an closed, NO resistance path that causes immediate wire overheating and blown fuses. Your low voltage (5-6V) is an indication of a high resistance path that is "eating up" all the electrical pressure (voltage), (like a kink in a water hose) so very little current gets through.

The suggestion to connect your meter's negative cable to the negative battery cable is spot on. You may need to employ a long jumper wire to do this. You could use about 20 feet of insulated primary wire (16 or 18 gauge) to extend your negative test probe back to the battery while you used the positive probe to check for voltage at any position in the trailer. I did this when I was troubleshooting a mouse chewed wire that was disabling my rear running lights.

A faulty ground connection will tend to disable multiple circuits, which is what you seem to have.

It's a tedious bit of troubleshooting, but for things to work, you need a complete, good path from the positive terminal of the battery, through the appliance and back to the negative terminal. Any weak connections in that path will result in low voltage and current or nothing getting through at all.

- Jack

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Hi-Lo 1707T - Tire Minder TPMS on Tow Vehicle and Trailer, 300W Solar Battery Charger, Equal-i-zer WDH, Progressive Dynamics Converter, Fan-Tastic Fan, LiFePO4 battery 12V DC Electrical System
2014 F150 Platinum 4x4 3.5L EcoBoost SCrew

use your jumper cable from batt neg to frame to provide a good ground as a test!