Proper way to wire a kill switch on Thunderbolt IV

[Broaters]

Hello guys,

we are currently towards the end of rebuilding our 1987-88 searay 20 Seville CC.
existing wiring was a mess with several layer of abuse and we decided to start fresh from the OEM engine and boat harnesses and to get rid of all the extra wiring.
Engine is a 5.7 Mercruiser with a thunderbolt IV ignition and I'm looking for the proper way to wire the kill switch.
I'm reading confusing info from the posts and the MERC service manuals.

Merc manual #9 says to install a NC kill switch between gnd and white/green wire on the distributor. This is what the shift assist switch does for temporary killing the power.
on the other hand lot of posts and other Merc literature says to install a NO kill switch on the purple wire to cut 12V to the coil.
Existing boat kill switch is a NC and i'm not sure if I should re-use it or buy another one.

What is the proper way to do it?
Thanks for your help

 

[Bondo]

on the other hand lot of posts and other Merc literature says to install a NO kill switch on the purple wire to cut 12V to the coil.

Ayuh,..... I think you've got yer NO, 'n NC backwards,......

Ya need a NC on the purple wire,......

Why would you want a kill switch in the motor box, as in yer other scenario,..??

 

[achris]

Are you talking about a 'dead man' style kill switch or the shift interrupt?

Dead man style should be at the helm, wired into the purple wire that comes from the ignition key.

The shift interrupt is a normally open switch which shorts the white/green to ground when activated...

Chris...

 

[Broaters]

Hello Bondo and Chris thanks for your answer.

My initial explanation is confusing sorry for that
.

what we want in the end is a lanyard kill switch at the helm.

The switch which was installed at the helm in our boat by one of the PO is a NC (i mean it closes when the lanyard is removed).
The only way to use this one is to wire it like the shift assist is wired and ground the white/green at the distributor to kill the engine.

To wire it in serie with the purple wire going to the coil i would need a NO (open when the lanyard is removed) which means I cannot re-use the existing switch as it only have 2 wires.

The second option makes more sense to me on the technical point of view and also because this would locate all the wiring in the dashboard.

in the manuals both options can be found depending on what book you read :
The Mercruiser manual #9 page 4E-7 shows how to use a lanyard kill switch grounding white/green wire.
However later manual like #17 page 4E-4 shows how to wire a lanyard kill switch in serie on the purple wire
of course they need to be the opposite type.

what do you think?
thanks again for helping

 

[achris]

...The second option makes more sense to me on the technical point of view and also because this would locate all the wiring in the dashboard.

The problem with using the white/green as your kill wire is that it leaves everything (dash instruments, coil and alternator) powered up after the engine is shutdown...

The kit outlined in Manual #9 is an emergency stop switch, and is located in the engine bay. It's for someone working on the engine for them to kill the engine if they need to.

A 'deadman' switch needs to shut everything off when it's 'pulled'. Depending on which remote control you have, there may already be a N.O. switch in that control.

If you are looking to use this as a valid safety feature, get the right switch and wiring it up the right way. Too many times I've seen jobs done 'to save money/effort' only to bite the person on the bum down the track, causing more damage, or injury....

Chris.........

 

[Broaters]

agreed our goal is to make it right !
we have been working on the rebuild for 3 years now and this is no time for shortcut.

I'll get a new switch of the correct type and wire it to cut the purple wire directly after key switch at the helm.

Thanks for convincing me
hava a great day

 

[Broaters]

our control is the old quicksilver like this one
don't think there is any NO in there.

the boat from the picture (not ours) have a separate lanyard switch

thanks again

 

[jbcurt00]

Closed