It has to be connected across the two oil sensor leads in parallel. So you would connect one wire from the 100k pot to the blue wire on the oil sensor, and the other wire from the 100k pot to the green wire on the sensor. I intend to make mine with plugs (scrounged from my old wiring harness with soldered leads) that match up to the existing wiring harness plugs and the oil temp sensor plugs for a "plug-it-in-and-play" affair. It'll be compact, weatherproof and professionally made.
Possible locations on the bike for putting it are somewhat flexible, since it can be plugged in under the oil sensor cover, or at the top frame tube where that sensor harness plugs into the main wiring harness. If you plug it in near the top frame tube, long chosen leads lengths could allow you to put it almost anywhere on the bike that is a relatively cool and dry area, yet is easy to access for quick adjustments.
You don't need to understand much about electronics... or anything else for that matter, really. Just do great work and you will always produce great products, that always work great. That is always true, no matter what you are doing.
Every oil temp sensor measures out at a different resistance than the other at the same temp... and every fan controller will kick the fan on at a different resistance threshold than the other at the same resistance... so there are no set "targets" for you to adjust the resistance signal that circuit sees to, from bike to bike. Follow me?
So, to allow for those differences between parts from bike to bike, the 100k pot you'll need is infinitely adjustable. You'll need to put the oil temp resistance mod on the bike and adjust the fan to kick on at (or around) a temp you'll choose yourself. You'll allow for a few degrees of range for the kick on temp target, because those oil sensors and fan controllers aren't precise enough to be precisely repeatable, to kick the fan on at an exact same temp every time.. I'll allow for about +- 10 degrees variance in kick on temp, for example, when I choose my target temp.
Does the pot affect the fan kick off temp?
Yes. If I understand the fan controller well (I think I do, I've built them from scratch before, with much tighter hysteresis, of course) the fan will be kicked out in a slightly tighter temp range than it would if left unmodded.
For instance: lets say the fan normally kicks on at an oil temp around 285 degrees (F) on our machine and normally shuts off when oil temp drops to around 235 degrees (F). The temp swing we are seeing from highest to lowest, is about 50 degrees on average.
We then add the mod to our hypothetical machine and adjust the pot so that the fan now kicks on around 215 degrees (F). We can now expect to see the fan shut down in less than a 50 degree swing from high to low... lets take a guess since we can't measure our make-believe machines fan shut down temp... say around a 40 degrees temp drop now... so around 175 degrees (F). So the hysteresis in the modded control system should tighten up some. We'll find out how much it tightens when one of us puts the idea to work in the real world.
The pot I tested this idea with was dug out of one of my parts bins, simply because it is an adjustable 100k trimmer pot. I'll attach the data sheet for that specific (size code is: 104) trimmer pot below, so you'll see whats going on here a bit better. But keep in mind that even though the Bournes pot that I chose to test this idea with is a good quality trimmer pot, it is rated for only 1/2 watts current handling max, if its working in a cool environment.
I will order a higher wattage handling 100k Trimmer pot to use in the real world application from mouser.com, because I want the pot to be reliable for decades on the bike.
Hope all this helps... Feel free to take the ball and run with it if ya want. I'd like to see how well it works on a 350. It'll be a while before I can finish up mine...