Hello. Just bought a 2016 Gem and the batteries were bad. I replaced the bank with 8-6volt golf cart batteries but when doing so i didn’t realize the single red wire for the 12V tap was a 12V tap and thought it was the battery charger wire and assumed it went to the 48V (+) and not a 12V (+). When i bought the cart i used 2-24V jump packs to test the cars functionality and everything ran as designed. After making this mistake and swap, i have no functions off the ignition and there is a beep under the dash (low voltage warning) im assuming. I have put the 12V tap in the correct spot and on the BMS module up front (I guess thats what it is) i have 12V to the correct terminal and 50V to the correct terminal. I still have nothing. All 12v fuses are good in the 12v termial but i only have power to the 5A “Drive” and the 30A “Chassis” fuses. Nothing else. I havent checked any relays yet and the battery charger when plugged in, doesnt seem to lock in and charge. Is there fuses anywhere else to check or could i have fried something that isn’t fuse protected by sending 48VDC down something that was a 12VDC circuit. If so what would that component be and how do i test or bypass? Thank you, Jeff.
Most likely smoked the bmc. If fuse keeps blowing, the cluster may be shorted shorted. There are also hidden components in the wire harness. Also heard of one that shorted the tone generator.
There was a recall for 2016 where the 12v tap was eliminated and a 12 volt battery was placed under the dash to do all 12 volt functions. Perhaps someone out there has that document handy. If not, I can try to locate it and post it here,
It’s TSB bulletin number L-18-01-B for model years 2016 to 2018.
I just don’t know how to get it off my iPad and post it here.
I’ve seen that on some. That would just keep idiots like me from tapping into the 48VDC incorrectly and just gives it another stand alone 12VDC source. I have 12V going into the BMC/BMS block but nothing coming out i’m thinking. I think that device may be cooked like Inwo said. Trying to get one from a buddy who has the same year to swap them out and see before spending $350.00. Just didn’t know if there were any bypasses or fuses i’m missing. Does the BMS provide 12 volt outputs to the fuse panel? I only have 12v coming to 2 fuses. All fuses and relays have been tested and work and everything was fine until i sent 48V down the 12V line.
Bmc has 12v in and 12v reg out to the rest of the controls.
All fuses are good? Do not oversize fuses. A shunt regulator, rev polarity protector is in the cluster and will melt if fuse is over sized.
Best case a fuse blows and by disconnecting devices find the short.
Good day Ledft
I have a 2016 also - the 12 batt in the dash is not charging, all other functions seem fine. I charge the 12v small dash batt with a trickle charger when volts get down a bit. What and where would this get its charge from normally? Do you have a schematic for this car? Thanks for any.
It looks like the 12 volt battery gets charged by dc/dc converter through a relay in the fuse box. The BMC controls that relay. As soon as I figure out how, I’ll send you schematics.
Thanks
I have other users, along with a fleet of 2016 E2’s used by a local University that seem to suffer the same issue - so a diagnosis will be highly valued!
Thanks
Tom
OK. Someone will have to try to help this old guy out. I’m trying to send you schematics privately because I’m not sure we’re supposed to post them publicly. However, I’m not able to upload a pdf file. Guess I need some specific direction. 
I’m not an expert. But I think the recall (or bulletin) was put in place because tapping into 12 volt out of your 48 volt pack keeps that part of the pack out of balance with the other batteries and eventually (prematurely) damages the pack.
Or maybe I misunderstood what you were doing to get 12 volts?