My univolt was exactly where yours was and it appeared to be toast from the last owner (there were hunks of aluminum foil where the fuses should be!) Not to mention the thing sat under the bathtub which was disintegrating. Super dangerous! It had to go.
The only purpose of that thing is to provide your trailer with 12V
DC and to charge your battery. In other words, the univolt is a battery charger with some fuses in it.
I replaced the entire unit with a 10,000W Uninterruptible Power Supply (nicknamed "The ARC") which is housed at the very front of my trailer; it houses 6 marine batteries, 4 2500W inverters, a battery charger, a breaker box, a 50Amp automatic transfer switch, a thermostat, and a wind-tunnel ventilation system. I can be plugged in, then I can unplug and the ARC takes control of the electrical providing all 120V AC and 12V
DC for the entire trailer for as long as the batteries have life (750Amp/Hours total). No appliance even knows the difference during the transitions e.g. the wii never even power cycled when I unplugged.
You can replace this system outright. Here's what I did:
1) Label the wires
**I have a 71. If your scheme follows mine, you're schema is as follows:
red1 & black1 - from battery
red2 & black2 - to ammeter control panel at the front of the trailer
grey - to indicator light in forward control panel
blue - charge line from tow connector to univolt
white - ground
purple - bathroom circuits +12V DC
yellow - middle area circuits +12V DC
pink - kitchen circuits +12V DC
brown - front of trailer circuits +12V DC
A) Go buy a smart battery charger. I got a Black & Decker 40A charger from Wal-Mart.
B) Get a fuse block. I got the Blue Sea systems 5025; it should also be perfect for yours. blue seas 5025 - Google Product Search
C) Get a big 'ole 12V
....Now you're ready to get rid of that archaic and heavy disaster.
3) Hook it up.
A) Connect the battery (anywhere) to your blue (+12V DC) and white lines (0V); (you can discard the red/black battery connections to the univolt; you won't need them)
i) your vehicle (through the tow connector) should now charge the battery
B) Plug in the battery charger and connect to the battery (consider getting battery terminal connections to replace the alligator clamps on the charger)
i) the charger (while plugged in) should be supplying the 12V for your entire trailer
ii) consider the idea of having inverters connected to the batteries to supply your AC power while you're not plugged in; if you do, please realize that you want to run a completely separate circuit that only powers when the trailer is plugged in. You wouldn't want your charger to supply power to batteries to supply power to your inverters which supply power to your AC which powers your charger. The Laws of Conservation unfortunately still apply.
C) Connect your fuse block and trailer circuits; you should have 4 different circuits, connect the blue line or positive side of the battery to each screw fuse block terminal on the left; connect each of your trailer circuits separately (purple, yellow, pink, and brown) to the screw terminals on the right. Add a fuse for each circuit and you're set! (You'll have to figure out the fuse you'll need yourself) You can do this by measuring the current through each circuit first while everything in the section is off (OAmps) and then when everything is on (xAmps); you'll want the amp rating on your fuse to be slightly greater than what you measure with everything on (fuse > x). Finally, connect the white wire to the ground bar on the fuse block.
**If you want your ammeter in the forward control panel to work still you will need to connect the red & black ammeter wires in series with your fuse block. In other words, the red ammeter wire would connect to your blue line or positive side of the battery, and your black ammeter wire will connect to each screw terminal on the left side of the fuse block (instead of the blue wire!!!). The ammeter is like a water wheel, you have to put this device in the path of current. This configuration will allow you to get a total current reading for your 4 circuits.
The only wire you should have left is a grey wire for the indicator light in the forward control panel. What a pointless connection... I'm going to use mine to multiplex information to a microcontroller.
If you'd like the indicator light to come on, just connect it to any +12V DC connection and/or through a switch (if you want to be able to shut it off).
You'll also have a dead ended romex (120V AC) now that connected to your univolt; I just put an outlet there.
I added a circuit diagram for a 71 as reference and some pictures of my configuration during the process.
And for anyone interested... a video of my homemade uninteruptible power supply: The ARC.
YouTube - The ARC