There are simple diagnostic techniques used to find full time shorts. The first is to identify the circuit and divide it untill the suspect is found. It helps to have some tooling. An interesting concoction can be made with some simple pieces. Wire a high wattage bulb through a two prong VW flasher (cheap doesn't need to be VW, domestic cars also use them). Hook the device between the fuse leads such that it flashes the light.

A compase following the harness with be distrated every time the field is made or broken. Without an inductive ammeter thats the best I can do.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician