You've been a huge help. The unit rated for 750 watts specifically says it's the fat tire MX US motor. The larger unit says MX US, but doesn't mention fat tire. Is there a difference? Would the larger controller (35 amp) have potential to harm the motor?
Sorry for newbie question, propriety ends jacks / connectors? When you say harness, you mean wires coming from motor to controller?
I am ready to purchase, once I decide.
Your first question, what is the difference, is beyond me. No first hand Bafang experience and I'd hate to steer you wrong.
No harm using the bigger controller. Might pay off if some day you decide to go with a BIG geared hub motor.
Ends/connectors = where the wires from one "thing" plug in to another "thing". There's no such thing as a universal connector, or even a standard, therefor expecting the thing you have in your hand to plug into what you need is not something you can take for granted.
The "harness" = all of the wires and connectors collectively
Proprietary= something specially built by the manufacturer for your bike. Not available anywhere else. The opposite of generic.
Bonus - the wire colors are generally similar, but there is NO assurance they will match either. What you can assume, is something like a PAS sensor for instance, will have 3 wires, and those 3 wires will have similar functions, no matter who supplies it. Like one will be + (positive), one will be - (negative), and the 3rd will be the sensor wire. This will be true on both sides, the controller side, and the sensor itself. Your job is to match those functions (positive, negative, and sensor). With a digital voltmeter, it can take longer to write out how it's done vs. the time it takes to do it. Same goes for the throttle and the brakes. Then you get to do the motor!
One nice thing gained from this experience, is you will gain an understanding of how your bike's electronics work way better than most!
Viewed one wire at a time, there's no rocket science involved - though when viewed as an entire functioning bike, some are convinced there is rocket science involved.... Just ask all the bike shops that are not interested in working on an e-bike - ANY e-bike!
Oh, and you can plan on anything coming from China to take 2-4 weeks. Just be patient on the tracking early on. -Al