My windscreen washer pump stopped working on my 1990 190E 2.6. The pump works if I jump direct battery juice to it. so its not the pump, So it is in the wiring, relay or switch. The wiring is buried and I don't have a clue where the relay is located. Any suggestions in my approach to this problem would be appreciated.

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1990 190E 2.6
1996 Grand Voyager 3.3
1985 Mustang GT 5.0 5 SPD
1982 Suzuki GS 750T