[njsteve]

Did you disconnect the brake light switch to see if the car still dies when the brakes are applied? Could be a 12v wire crimped against the firewall by the brake bracketry - when you apply the brakes, the bracketry shifts and grounds the wire and backfeeds the car into a 12v positive ground system.

When I pulled my 69 Z11 pace car apart I found a main power lead wire from the dash harness clamped between the brake/clutch pedal assembly and the firewall. It would have eventually caused one helluva electrical fire.

Also, one of the brake light bulb assemblies themselves could be internally shorting to ground when the power goes to the bulb. From experience I know the Mopars are extremely sensitive to a bad ground on the tail lights - so bad that they backfeed all the other lights in the car when the brakes are applied, if the ground is not good enough.