I received the vesc controller box today. But no power. If the existing fm bms is connected, is it correct that the power does not come on? I’m really curious.
Correct. The BMS requires a momentary short provided on the blue signal wire. Usually this comes from the momentary power switch. The Makers PEV latching power switch will not work to turn the BMS on. In fact- it is designed to turn the foccer off. (the lfoc is ON by default)
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Thank you very much for your reply. So, the solution is to get a new bms or do I need to do a separate job?
you have a few options -
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change the power switch configuration so it is a momentary that actuates ground the to the blue wire of the 16 pin harness. this will turn your FM bms on. now you have to worry about enabling balancing (purple wire) and whether or not to enable charge-only (isolate charge/discharge paths)
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get a different bms (xlite ennoid, zbms, others tbd). will require some effort.
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remove the bms. this is the ‘easiest’ solution. by easiest - i mean involving the least amount of effort and getting you riding immediately. just remove the bms and power the foccer straight from the battery. you can keep the vesc controller box and power switch in tact for this configuration. you’ll be forfeiting other features that come with a bms however. some say this option is not safe. you can consider a daly external balancer to balance your battery cells on occasion.
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Let’s try the above method. thanks for the answer 
Grtting my pre assembled box in few minutes, ordered a momentary switch which will arrive today as well. Do i just take the latching out replace it with a momentary wire for wire???
Disconnect the bms from the battery pack and connect it directly to the battery to drive.
I got it going last night, but today saw the one dude wired the wire to the slr as well for balanced charging??? I want to say i has it wired like that but things wouldn’t turn on soo i disconnecting the slr wire and worked