1970 Mercury 50hp Will not turn off

[Dave O]

Hello Everyone,

I have a 1970 50hp Merc 500 that will not turn off. I replaces the engine side wiring harness as well as the throttle control box (replaced with a Quicksilver MSC4000 Side Mount Control Box and the boat side wireing harness adapter).

I will be replacing the mercury switch this weekend.

Most of the wiring on the engine side and boat side was dry rotted or corroded and falling apart to the touch when I bought the boat last year. The original emergency cutoff was separate from the control box and I removed it since the new control box came with a cutoff switch as part of the box.

The engine started right up after not being run for three years, but when I tunred the key off it would not shut off, I disconected the battery, and then the fuel line to get it to shut off.

Any help would be greatly appreciated.

Thanks Dave

 

[jarand82]

Re: 1970 Mercury 50hp Will not turn off

The wiring diagram at maxrules.com for the 500 merc. with thunderbolt ignition
says that the tan wire from the "KEY SWITCH" to the switchbox is your "kill" wire. When u turn the key to the off position it connects this tan wire to the black ground wire to stop spark to the engine.

Here is the link to the diagram.

http://www.maxrules.com/oldmercs/Wiring/1966ona/26.jpg

 

[Dave O]

Re: 1970 Mercury 50hp Will not turn off

I found the problem. After going back and looking through my manual and at the wiring diagram i found a wire that was disconnected. As soon as I connected it the motor wound turn off with the key or when I activated the emergency stop

Dave