Since your 1989 Volvo has separate wiring(meaning the brake and turn signals are sent along separate wires) I recommend the Vehicle Wiring Harness Kit, part # C59496.
To install this harness you will need access to the wiring behind each tail light. Starting on the left driver side, you will need to find a place to mount the converter box. Then, ground the white wire to a bare metal surface.
Next, you can use the included circuit tester to check the wires until you find the one that... view full answer...
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