77 1150 Orange wire

[MatthewtheDruid]

I was hooking the tach wire to my rectifier for an aftermarket unit, no problem but I realized there’s this orphaned orange wire. Its connector is tapped so it’s never been hooked up. The engine runs, starts stops. So I’m stumped. On a wiring diagram I see the external harness has an Orange. Connects to ground when you shut off but the internal has no matching wire shown... soooo. Anyone know what this is?

 

[Chris1956]

On a 1977 (or older) Merc Inline 6 motor, the ignition is battery powered CDI, using a distributor. The ignition is killed by depriving it of voltage.

The orange wire grounds the ignition of Mercury motors with multiple coil ADI ignition. It is unused on your motor.

If you were to get a motor of about the same vintage, with ADI ignition, the same wiring harness you have would work, because you have the orange wire available.

 

[MatthewtheDruid]

Thanks, so other engines in 77 used adí which is killed by grounding out but they used the same harness because it’s probably cheaper to have one fairly generic one than a dozen slightly different ones produced? Better that than missing wires I guess.
cool. Kinda suspected but wasn’t sure.

 

[Chris1956]

Yes, the 4 cylinder Mercs (80-85HP) went to ADI ignition in 1975. The 90-115HP inline 6 motors converted to ADI ignition in mid-1979.

Not sure about the other Mercs.