This Auxiliary Power Supply (APS) sub-assembly is a DC to DC Converter that converts the 400 Volt DC pack voltage to 12 Volts DC to power Roadster electronics, headlights, audio, VMS Module, Window Regulators, Door and Trunk Actuators, and charges the 12 Volt auxiliary battery which resides inside the Passenger Fender.
It was originally made by Eaton, Martek, and Delta Electronics. It is a custom part, made for the Tesla Roadster, and includes the same plumbing as the ESS Battery Pack Sheets. To service this assembly, a battery pull is necessary.
Tesla may have dwindling supply left. Spares are often harvested from donor Roadsters, the supply of which is also steadily declining. Even if a replacement is found, they have aged and are most likely full of deferred maintenance issues.
Fortunately, this part is repairable and rebuildable. We have successfully reverse engineered this sub-assembly, and are offering full rebuild services.