Get to know the 12 volt DC system that powers the electronic controls for the appliances, alarms,fresh water pump and interior lights. The converter/charger charges the house battery(s) when the rig is connected to "shore" power. There is a switch that disconnects the house battery so that it can stay charged without parasitic loads like appliance controls and alarms while the rig is not being driven. Your converter charger may need upgrading to a modern one that will not overcharge house batteries. House batteries may need replacement if they are old and/or have been left discharged or if electrolyte levels have not been maintained with distilled water. Check house battery voltage with a voltmeter set for 2O volts DC. With rig connected to shore power or with generator running 13.6 volts, with engine running 14 volts, disconnected from shore power, engine not running, approx 12.6 volts. Expect problems with poor 12 volt connections (corroded, loose) in the 12 volt DC system on an old rig. Your engine starting battery is not kept charged when rig is connected to shore power unless a BIRD device or other device has been installed.
Check brake system for sticking calipers and engine cooling system for water pump, radiator, belts, hoses, and "clutch fan". Tires older than 5 years old may be unsafe, check DOT date codes on each and check for sidewall cracks that can lead to tire failure on the road with possible loss of control. Replace old flexible brake lines that can fail internally and cause loss of steering control,and replace brake fluid. Oh, Check dash AC and dash heater operation, and entire house plumbing system including the toilet, faucets, and holding tank dump valves and sewage hose fittings.
There's lots more to know and deal with on an old rig , good luck with your new hobby. It's a roadable motor yacht.
Last PS: Get the maintenance manual for the van that your rig is based on. RV Owner's manuals if you have one, are usually generic and don't include detailed electrical schematics and details as needed for troubleshooting. You may find good "how to" info on You Tube.
