Normally-high run switch vs coil-ground out to turn off

Question

I'm restoring a 1958 larson Playboy - it looks like it originally came with an evinrude engine as there was an evinrude starter solenoid box in the back. This was cabled into the main key which has three positions - off, run, start. The pinouts are as follows:

• off - 12v connected to nothing
• run - 12v connected to one wire, which runs into the starter box
• start - 12v connected to both wires

My understanding is to shut off a small engine, the high side of the coil is tied to ground, so this switch behavior is confusing.

The previous owner was partway through the work and it looks like they installed a switch specifically to get around this - this switch was wired with the intent to ground out the coil.

I'd much prefer to use the original key system if possible - is there an easy way to accomplish this? The only thing I can think of is to use a normally-closed relay and have the key being in "run" hold the relay open, but that seems like an active solution to what should be a passive problem.

The new motor is a ~1980 mercury thunderbolt 40HP

edits

The new motor has an 8 pin connector, and as far as I've pinned it out, has:

• 12V
• Ground
• Starter solenoid signal
• Choke solenoid power
• Ignition kill (kills when grounded in the original ignition)
• Tachometer

There's an accessory pin and a prime pin as well, but this motor does not have those features.

Answer 1

From the information you have provided, I cant see any other option other than what you have suggested of using an normally closed relay that is operated by the run position of the switch.

Without this relay, I can't see a use for the output of the run position of the switch. The 12v connection to the motor sounds like it needs to go directly to the battery to carry the large starter motor current. The start position will operate the starter solenoid.