Key switch replacement which one do I need?

[Dentcrew]

Have a 76 Thunderbolt 850 w/85hp but newer (unknown) mercury control box with an 8 pin/wire harness. Doesn’t have tilt/trim. Have no idea what model/type key switch to replace it with. Motor won’t run with kill wires hooked up to switch box. Suspecting ignition switch unless there’s a way to test b4 I replace?

 

[Chris1956]

Any Mercury OEM switch will work, as they are made to be universal. A 1976 Merc 850 should be 4 coils and 1 switchbox. A magneto-type ign switch should be in it, if replaced with non-Mercury.

The ign witch should unground the ign killer wire (orange or salmon on motor, and possibly black/yellow on control).

 

[Dentcrew]

Thanks Chris1956, you've been a BIG help. Do you think the Key Switch could be the only issue, as it also has a Toggle Kill Switch on the control box under the key switch as well?

 

[Chris1956]

Toggle Kill Switch? Not sure what that is. Original MerControls did not have that. What do you have?

 

[Dentcrew]

Here's a pic. It's a silver "Toggle" style switch under the key. My guess it's a "Safety/Run" Switch?

 

[Dentcrew]

I checked all the Key Switch/Ignition Switch wires, and all function correctly. Then I disconnected the Yellow/Black from control box to the Grey (Choke Solenoid ) to the engine, everything worked perfectly with the Kill Wires connected to the Switch Box. So, as of now, everything works as it should. BUT, from the control box harness, I still have a Tan/Blue Stripe Wire and a Yellow/Black wire not hooked up. And from the engine, I have a Grey Wire (Did confirm it's the choke wire. So, as you can see in the photo, I have a "run" silver toggle switch at the bottom, then the Keyed Ignition Switch, and I have NO idea what the top one is: Has that Tan/Blue Stripe Wire and Purple Wire coming from it. Any ideas?

 

[Dentcrew]

BTW, the ignition switch is a 6 wire:
Red
Black
Yellow/Red
Yellow/Black
Black/Yellow
Purple

 

[Chris1956]

Itis hard to see, but it looks like the lower switch has black/yellow and black on it. That makes it a kill switch. Maybe some sort of lanyard used to fit on it, for safety?

Anyway, your control has the new wiring colors and your motor will have the old wiring colors, if the harness is original, or replace with an original one.

Black and red are ground and |12VDC battery.
Yellow/red is starter solenoid, engine was solid yellow
Black/yellow is ign killer, engine was orange or salmon
Yellow/black is choke, engine was grey
Purple is ign power, your engine probably doesn't use it, but the original wire color was white
Grey is tach signal, engine was brown

Hope it helps

 

[Dentcrew]

Thanks Chris, the : "Yellow/black is choke, engine was grey" is the one I disconnected, as with it connected, the engine would crank, but would not start. It's VERY weird I know. So, I just left it disconnected, and everything works as it should, ignition wise. I know the choke solenoid is missing the plunger, so doesn't work anyways. So I just use the manual choke. I'm just glad it's back on the water! I appreciate all your help!