MilesFinn said:
I was hoping for a document laying out the controller's cables, including the purpose of each (e.g., + 5V, gnd, or "connect to speed potentiometer") , its color, and the connector type.
Very very few give this info. Grin Tech at http://ebikes.ca has it for most of their stuff. It's the only seller I've got any experience with that does. EM3EV may also do this; I haven't checked them in a long while.
Some controller manufacturers like Kelly provide this kind of information, but they are the manufacturer...they are one of the few that will sell to individuals. Most only sell to OEMs; you can buy their stuff (Sevcon, ASI, Mobipus, etc) from third parties but you're pretty much completely on your own at that point (no support, no documentation, software, passwords, etc; they only deal with OEMs on that stuff, not individuals).
But I've got to think that that there must be a lot of these controllers that were purchased but never successfully wired.
That's almost certainly true.
Certainly seen it happen enough here on ES.
Is there a standard for displays, or do you need to buy a display that the controller vendor promotes?
THere are no shared standards. Not even a guarantee that the same brand of display works on the same brand of controller; they may have different firmware versions, or even not be designed to work with each other.
There is a sort of standard in that most of the controller/display sets communicate via a serial RX/TX two wire bus, and use battery voltage and ground from the controller, and control anohter battery-voltage-level keyswitch-ignition (KSI) line back to the controller to power it on remotely from the handlebar controls. They even often use the Julet / Higo 5-pin "green" connector for the waterproof cabling sets, and may even use the same wiring of that connector.
But the serial protocol may be different, and even if it is the same, the data being sent will be different for different controllers, displays, firmware versions, etc etc.
Then there are different sellers of the same brand, who may have custom versions of them, that don't even have the same settings available in the menus, or the setting means something different in one seller's version vs another.
Then there's the stuff that comes on OEM bikes, sometimes developed by that OEM, sometimes not, that only works with itself.
Etc.
There are some controllers that work with multiple models of display, and vice-versa. But to be sure what will or won't, you'd probably have to search ES to find out if someone successfully used Controller X from Vendor A with Display Y from Vendor B. (it could make a difference where it's purchased from because some sellers do have their own versions of things).
Then there are the several Open Source FirmWare (OSFW) projects here on ES, to replace the software on various controllers and displays to *make* them compatible, and to give features the original didn't have (but which the hardware supports).
This whole industry is in serious need of standardization.
That is almost certainly never going to happen, at least partly for similar reasons that Ford parts don't fit Hondas, or Kia parts fit BMWs, etc.