It is not in the service manual.
It's in the rigging guide, however it's vague. Look for a tiller installation guide, I found it there. Ask your dealer if you can view their 2017 or 2018 rigging guide. Don't ask 'em to borrow it unless they offer but they should let you have a look at it. It kinda halfway give you an idea where it's at. Usually behind a plastic cover or laying in the lower pan.
I assume you're speaking of the variable trolling feature (VTS)? On the 25's and 40's it's right in the front of the cowling lower pan. The plug for it has a cap in it. I can't remember if it's a white plug or a blue one, but it matches up perfectly with the connector for the switch harness, and it's the only one that matches. They do a good job of burying it but once you find it, you'll have that proverbial "ah-HA" moment. Be sure to make sure to tie it up so it can't contact the throttle & shift linkages. I had someone call me a while back who ordered a tiller kit for a F40 with VTS and he didn't tie up all the wires. One of them got hung in the shift linkage. When he went to reverse, it cut into one of the PT&T wires and blew the fuse instantly.
