I have a 1986 740 wagon thats non turbo. The wires going to the hall effect sensor have broken. I want to repair them with a back up connector but the 3 wiress are insulated too tight in their line. Where do the blue, black, and red wires eventually feed into? I have some sources saying the power stage but the colors on the power stage dont match and the insulated three wires contiue past the harness into the drivers side of the fire wall then disappear in the sea of wires.

 

Not the Power Stage. Probably the ECU. It's been awhile since I dealt with that issue but I remember the wiring from the Hall Sensor being a coaxial type cable. When I did it, I just made a good connection with the main "middle" wire and wrapped up the insulation around. It was an '85 740... Should be the same as an '86.

 

Ive tested the wiring at all pin outs at the ecm connector and had no continuity results showing me where the 12 volt ref or signal wires end up. Im also not sure if the ground rapped around the red ans blue wires can just be attached to any ol ground or a specific one in the ecm. I know that coaxial cable stretches all the way thru the harness, underneath the steering wheel then awhile towards the glove compartment.

 

The wire goes imto the ignition module under the dashboard, not the ecu, it is a separate module. you can splice into it just use butt splices and connect the wires including the bare shielding wire.

 

indeed, its shielded 'twinax' with two conductors and an outer ground shield. the output of the hall sensor is a very small signal and needs to be shielded from noise. as 86744ti says, it goes to the ICU, which is behind the dash, either on the glovebox side, or the driver side, I forget which on that generation.

 

Wiring from hall sensor actually run all the way to the ignition control unit underneath driver side dash. Black box 6x6 inches. Good idea is to just rewire as far back toward firewall as you can. Make sure your connections are tight because they send and receive signals from ICU unit I mentioned

 

the hall sensor cable is a shielded twisted pair, aka twinax. the signal is on the twisted pair, weak low voltage high impedance differential signal, while the outer shield is a ground, and keeps the signal quiet and clean, free from electrical interference.