70s merc 850 85 hp mercontroller

[Hotrod758]

I have a 85 hp merc 850 with the original mercontrol shifter box I want to upgrade to a new control box keeping the side mount does anyone know which one would work bot worried about the wiring I should be able to wire anything to work more worried about the cables and such being a fit any help would be much appreciated idk if anyone on here has swapped the mercontrol out for anything if so let me know what ya used

 

[Chris1956]

The mechanicals (shifter and throttle) of the newer Mercury controls will work just fine. The wiring is also compatible, but the connection to the motor is quite different. The newer boat harnesses have a round 8 pin plug, with 2 bullet connectors for trim and tilt. The extra wire is for overheat warning, which you do not have. You will also need separate battery cables, as they are not contained in the new harnesses.

You can graft your old quick-disconnect plug onto the new wiring, or possibly replace your engine harness for one that matches the new boat harness. I would recommend the latter.

Most engine harnesses of motors that old are pretty bad. The insulation is falling off. The wiring colors have changed over the years, but the function of the wires has not.

 

[merc850]

You have the wiring harness take the box apart and check the wires if they're bad and you have extra just cut them and wire to the new control switch. Newer controls short the switchbox to ground to stop, yours puts + power to switchbox and removes it to stop so you have to figure that one out at the switch.

 

[Faztbullet]

Either buy the adapter or use the purple to power the white wire.