Confirm you battery, cabling and related buss bars are OK and tight.
Your symptom can occur if a back up alarm has been connected to the reverse circuit incorrectly.
Check the brake pedal wiring/switches and return spring, when reversing sometimes the pedal will move cutting out reverse traction.
I do not recall a dash circuit breaker on those old electrics. Unless it was installed to resolve some electrical short. Send to my profile the full model and serial number. May have some old wiring diagrams for your unit.