On my 2004 Monterey tank gauges quit too.
The Aladdin system has modules scattered around the rig. Turned out the problem was the module in the tank bays.
On mine that module is located behind the first door forward of the right drive wheels that does not have the regular handle. It has hidden latches at the bottom. Beaver put it together so that when I drove in the rain water flying off the drive wheel penetrated an unsealed gap between the wheel well and tank bay. The module was attached in the perfect spot to get the brunt of the water spray. Since I don't drive in the rain all the time, it took about three years for the effects of the water to kill the module. I got it replaced at a Monaco sponsored rally when they were still in business. The Monaco tech replaced it and said I would get a bill for the part, but I never did. The only trouble shooting he did was to see the muddy water on the module and decide it was ruined.
It may have only been dirty. Cleaning of the plug and socket contacts may have been all that was necessary.
With the new module I created a "rain hood" for it with duct tape because I couldn't find the leak. (Honest!) I bought several cans of undercoat and worked on the wheel well, but that didn't work. Finally, last year (just before the Quartzite Rally) I spent a day poking around with a putty knife and found that the top front corner of the wheel well had enough space for the putty knife to easily slide into the tank bay. I sealed it and for the first time in 80,000 miles the module and the rest of the stuff in the tank bay doesn't get muddy anymore.
With old Monaco out of business I don't know where you would buy Aladdin parts other than to try Beaver Coach Sales.
