[fintubi]

In the particular case of the slabside cars, there's a technique given in the wiring manual which is functionally the same as RockBit's solution but even easier to implement:

On the slabside harness, the + and - ammeter connections pass through a duplex Powerpole high-current connector under the dash on their way to the meter. Since Powerpole connectors are genderless, the two poles on the firewall side of the connector can be plugged into one another, creating a direct connection from the circuit breaker to the fuse block. The pin stacking the two poles into a duplex has to be removed, and some tape unwrapped to give enough slack, but otherwise easy peasy. And reversible!

Bill