Western Star jake wiring

First of all, new user. Hello everyone.
Looking to install an EasyJake switch on my shifter. According to the instructions that came with it, I have to look for the "switched hot line", but I dont have one according to my test light. I tried putting the switch in line with the 'constant-hot' wire, but that didn't work. Just wondering if anyone knows which wire I need to tap into. There are 7 wires on the main on/off switch, one of which is constant-hot. There is one wire that goes from 1.7v when off to 0v when on.
It's on a 2011 4900FA. Thanks for your time fellas.

 

Hey Cetane+ thanks for the reply. This is the back of the on/off switch. The grey wire is the constant-hot. There is an unused stud that switches hot, but putting power to it doesn't change how the jakes engage, meaning - the dash switch still needs to be on and the add-on switch does nothing, except it turns on the little light.

 

According to the meter, I get roughly 1.5v from red to black when switched off, then goes to 0 when switched on. I tried the jumper wire from red to black when unplugged, as well as a couple other combinations, but they didn't engage.

 

Sorry, it does work, jumping those 2 wires. When I tested it before, the truck wasn't up to temp. It doesn't let me use cruise either until it's right hot. Also, I think my brain was getting hung up on the concept of "providing power to something" in order to make it work, instead of just closing a low-voltage loop. Only thing is, the light on the add-on switch doesn't light up. Small potatoes though. It would look good with the other red lights going into it. The main goal was to be able to switch the jakes on & off without taking my eyes off the road. And to keep me from looking like an idiot when that dd15 throws me against the door when I forget to turn them off. I went from a 93 T800 to this truck, still getting used to the electronic throttle.

 

Thanks for your help brother.