1969 Chris Craft Roamer Refit: Engine Wiring IV

With the OE Chris Craft wiring hooked up to the interface panel for the Cummins engines, next I need to dig into the Cummins loom and also install the senders for my completely refurbished Chris Craft gauges. But first, I wanted to install some sort of neutral safety switches. I spent a lot of time over the last few years wondering what sort of switches I should use and how I should place them so the switches would interrupt the start circuit when the gear levers were engaged either way. Then one day recently, I realized that the ZF gears I’ve got come with built-in neutral safety switches! That’s much better! But for some reason, the neutral safety switch wiring in the Cummins engine harnesses terminate in  factory-installed dead ends. All I had to do was modify the wiring so the neutral safety feature will work from the Cummins panels I will one day install in the engine room or from the Chris Craft helm.

An unloved neutral safety switch

Pretty simple device

Something inside the gear pushes on the ball, which breaks the circuit in the switch when it’s put into gear. Nice and simple design.

Failed switch or failed screw?

I found many forum discussions on the internet about these switches failing. But it’s a simple design that seems fairly robust and is used by ZF, Paragon, and other marine gear manufacturers. Based on what I saw on my switches, contact failure at the steel washer is the more likely cause of switch failure. I bought new ones anyway, and found prices ranged widely: many sellers listed the switches for $50 or more under the ZF brand name. I ended up picking up a set of Paragon branded switches for $17 each.

Digging into the Cummins loom

It’s pretty obvious somebody has been in this loom before. It appears that when they installed the 20′ extension, they clipped the wires rather than just plugging the OE Cummins connectors together, which makes no intuitive sense. They didn’t even bother to use shrink connectors. Either way, the white wire comes from the neutral safety switch to the connector for the Cummins panel. There’s also a black wire that goes to the neutral safety switch, but it enters the loom and heads away from the connector. Hmmm…time to dig in.

That cloth electrical tape is good stuff

The black wire stays in the main loom that passes under the turbo

Ah-Ha! All of the grounds come together at this one connector under the turbo

The Cummins schematic didn’t show all grounds connected at the same point. I’d been trying for a while to figure out where all the black wires tapped into the ground circuit. It wasn’t apparent until I opened up the loom in the most inaccessible place on the block…under the turbo.

Don’t need the 20′ loom extension anymore…

But I do need the factory connector at the far end of the extension

I know where each and every wire goes!

I plan on using Cummins’ wire scheme for all of the Chris Craft senders I’ll be adding to the engines, so purple is ignition, red is 12vdc+, brown is water temp, etc. The 20′ extension harness will provide the wiring I need.

Hello. What’s that about “MARINE WIRE”?

I was surprised to cut back the insulation and find bare copper wire, since I always thought a hallmark of marine wire is that it’s tinned. I guess if you’re buying wire by the truckload, you can order whatever you want printed on the outside of the insulation.

New safety switch terminal

The neutral safety switch completes a circuit to ground when the gear is in neutral. When the Cummins’ panel sees ground on the neutral safety circuit, it activates the Start circuit, so when you hit the START button 12vdc+ current passes to the aux. starter solenoid and the internal combustion magic begins. But on the Chris Craft side, the START circuit is always hot. So to get the two to work together, I believe all I need to do is to cut the ground from the aux. starter solenoid at the big ground connection point under the turbo, then add a separate ground line from the safety switch to the cut wire. That way, even if the START switch gets hit up at the Chris Craft helm, the ground side of the  circuit will be interrupted if the gear isn’t in neutral. The Cummins side is wired per the factory schematic, so it should be unaffected by this.

With the neutral safety circuit pretty much done, I installed the Turbocator wiring and boost lines since they also have to join up with the loom that goes under the turbo…and I never want to have to dig into that ever again.

Turbocator wiring & boost tubing

Turbocator cable/boost line goes into a loom

Thermocouple wiring is almost done

I was so impressed with how difficult it was to remove that cloth electrical tape that I ordered a couple of rolls, along with some 1/4″ and 3/8″ split loom.

Thermocouple wiring is ready to go

And that’s a wrap

All of the engine wiring is done now. In the pic above, you can see all of the Cummins wires on the right side of the terminal block, with the Chris Craft wiring on the left side. The next step will be to install the various senders that work with the OE Chris Craft gauges.

Next up on our 1969 Chris Craft Roamer Refit: Installing Chris Craft Senders on Cummins Engines