amesser325

I've been working on retrofitting the tow module (and manual hitch) to my '10 535xiT. I bought the latest AHM, which is the 4R version that has 20 pins in the connector and two +12V inputs. After a ton of searching I couldn't find a factory harness so I set about making my own - did the wiring research, bought the right pins and connectors etc then set about the install. When I first powered the car up I got a bunch of CAN errors but realized I hadn't yet added $235 to the VO (And default .MAN into the used module), so I did that and seemed to get the errors to go away. Problem is every output is now on - trailer light brake, turns, tails, rear fog, reverse. I'm confident of the wiring with the exception of pins 9 and 10 on the connector, which seem to be Right Brake In (taken from right rear brake light - seems to be a backup in case of CAN failure) for pin 9 and pin 10 is LM input that comes from the Black/Yellow wire in the bundle above the rear fuse box. Interestingly it doesn't have voltage (actually around .7V), but I wonder if it's a message wire similar to a CAN wire.


Anyway, I don't get any errors in Check Control, I'm able to read/write to the AHM module in NCS (and the few parameters don't relate to channel output), and I had an early error in ISTA + but performed the recommended action (it ran diagnosis) but no issues found and with a clear codes action the faults didn't come back.. The AHM board itself looks fine, or at least doesn't look like any of the components on it let out the magic blue smoke, and according to realoem is the correct 'latest' module for my VIN.
From what I can tell, the changeover from the AHM3/3+ to the AHM4R was to address higher electrical loads since it adds a second +12V supply to the board (which I wired). There are significant pinout changes between the two modules so I can't just swap in a 3+ module but if that is what will fix it I'll do it. Of course, I'd also have to buy another module that I'd like to avoid as an unhopeful troubleshooting step.
I didn't find any other posts with this problem and nothing on a wider google search turned anything up.

Anybody have a similar issue that was fixed, or perhaps have a suggestion? The only other thing I can think to check would be to run a wire directly from the LM (pin 29) to the AHM (pin 10).

Thanks,

Andy