70's Merc 850 Kill-Switch Retro-fit

[rgrycki]

I've searched the forum for a similar post and couldn't find an answer, so here goes. I got a mid 70's Merc 850 T-Bolt a few weeks ago an a '72 Starcraft SS 16'. The guy says it was a '79 motor, but after some research I found that the 850 wasn't made in '79.
I want to install a kill switch that I bought, but I'm not sure how to connect it. The switch has a red wire and a back wire coming from it (it is a hooded toggle switch that captures a small plastic d-ring). I am re-wiring the wire harness since the insulation is old and crumbly and would like to do the retro-fit at this time.
Any help provided would be much appreciated, such as connect the salmon wire in parallel to the red lead and the black lead to the ground bus etc.

 

[usskydvr]

Re: 70's Merc 850 Kill-Switch Retro-fit

What is the ser# of your engine? Do you want to wire in the kill switch to the Control or go back to the engine?

 

[rgrycki]

Re: 70's Merc 850 Kill-Switch Retro-fit

The serial # is 4100xxx. That means it's a '75 right? Anyways, I would like to wire it to the controls. My last resort was to use a continuity tester and find out what wires the key used to shut the motor off when turned to the off position and try to replicate that circuit path with the kill switch. However, I don't want to do anything that could cause damage. the guy I bought it off of said the power pack is sensitive to voltage variations.

 

[Faztbullet]

Re: 70's Merc 850 Kill-Switch Retro-fit

First off the "kill" switch must be checked to see if its NO(normally open) in run position(up) or NC(normally closed) ,if closed it will not work. You will need a NO switch with one end to ground and a wire ran back to engine switchbox and tied to the brown wire on trigger side. Someone will say you can break the white lead(12v to box) but Mercury did not recommend this and that why the OEM "kill" switch ran all the way back to engine.

 

[rgrycki]

Re: 70's Merc 850 Kill-Switch Retro-fit

Uggh, sounds like a pain. I'm assuming this means there is no way to do this from the controls. Is there any trick to running this wire from the inside of the cover to the outside without cutting a hole?
Oh yeah, the switch is NO.

 

[Faztbullet]

Re: 70's Merc 850 Kill-Switch Retro-fit

The salmon wire is not used in a distributer motor,the only problem is the internal wiring harness is not pinned out for it. If your not going to use a tach you can use the brown wire(hope you really use tach) other than taht you will need to run seperate wiring.

 

[Moody Blue]

Re: 70's Merc 850 Kill-Switch Retro-fit

I did what Faztbullet mentioned not to do.

I interrupted the white +12V wire inside the controller and ran two wires out to my kill switch (N.O.). There is a convienient 1/2 moon shaped opening at the bottom front of the controller housing just big enough for a 1/4" split loom wire harness out to the kill switch.

The kill switch effectively interrupts the switched +12V to the switchbox in the engine. Was no need to run a separate wire back to the engine.

Faztbullet, do you know why Merc recommended against this approach?

 

[Faztbullet]

Re: 70's Merc 850 Kill-Switch Retro-fit

I cant really recall but I think it had to due with switch getting dirty,resistance and voltage drop to switchbox imput causing problems/failure.

 

[usskydvr]

Re: 70's Merc 850 Kill-Switch Retro-fit

Interrupting the voltage to the White wire is essentially what happens when you turn the ignition switch to the off position (and for those harnesses that feed the salmon to the engine, it (the salmon) gets grounded too)

 

[rgrycki]

Re: 70's Merc 850 Kill-Switch Retro-fit

I wired it up and tested it out. It works great! Thanks everybody.

 

[Moody Blue]

Re: 70's Merc 850 Kill-Switch Retro-fit

So how did you end up connecting it?

 

[rgrycki]

Re: 70's Merc 850 Kill-Switch Retro-fit

Red wire to trigger side brown, Black wire to engine housing/ground.

 

[Moody Blue]

Re: 70's Merc 850 Kill-Switch Retro-fit

So you ran two new wires back to the switchbox from the killswitch ?

 

[rgrycki]

Re: 70's Merc 850 Kill-Switch Retro-fit

Yes, I was able to run them through the gap between the front cover and the rear cover.