RV Electrical Nightmare

I recently purchased a 1992 Holiday Rambler Motorhome. It has a 3208 Catopillar diesel engine with 51,000 miles. Everything seemed to work fine except it had a drain on the batteries for the chassis and the batteries would not start the engine after it sat for a couple days. After cleaning the battery cables and reading the manual I realized the batteries (2 huge 12 volt batteries) were installed wrong! They were hooked up in series (24 volts) and the owners manual says it is a 12 volt starter on the engine. So I hooked the batteries up in parrallel 12 volts. Now the starter workes fine, but all my accesories seem to be quiting! First the security system stopped working, then the radio, then the lights for the heater/AC control, and now the Gauges for the fuel and volt meter are not working properly. They seem to be getting current but the fuel gauge goes all the way to full (I actually have about 1/4 tank), also the volt gauge moves up to about 8 volts with the engine running), also my backup moniter will not come on, and the dash clock has stopped. This motorhome has about 50 plug in fuses that seem to be OK, also it has about 10 breaker fuses that seem OK, but there are about 10 Bosh relay fuses that I don't know how to test.I have cleaned all the ground connections I can find and am now wondering if a relay fuse could be the problem? I also replaced the ignition wire (about 6" from a plug connector to the switch as it was spliced and had a very poor soldering job. It has a Chevrolet ignition switch but seems to work just fine as for starting the engine, and having current to the accesories. Please help if you can. Thanks Graystation.