If your Ambassador originally had an battery it would have been mounted in a battery box on the front of the trailer. These were long batteries, approximately 6" wide and 18" long and often referred to a tractor batteries. Most your lighting is 120 V AC. If you have dual lighting fixtures, then one is at 120 Volt AC the other at 12 Volt
DC. The Univolt converter with 12 volt
DC output was not installed until 1965
, therefore battery charging had to be through either the TOW vehicle or by using a seperate battery charger. You will probably have to build a battery box to be mounted on the tongue or install an AGM type battery inside. Also will need a converter such as Progressive Dynamics Intellipower.