voltage reducer connection

[IcyFrog2]

ok I know everyone in hear has heard this and that with voltage reducers/converters but this one is a stump I have a 2005 48 volt club car DS IQ I have done multiple enhancements on it and put my heart into it first rebuild was new batteries and a stereo with amp in back and some led lights in front using a Nivel 9020 voltage reducer/converter running like instructions said 48 volt positive to battery No.1 and 48 volt negative to battery No.6 no problems at all on this setup now I turn around and really get into it and order a led full street legal light kit well I decided to add a second reducer just for lights and front accessories like 12 volt outlet for plugging in chargers for phone etc. , while the Nivel will only be running stereo and amp. I take things slowly and my wiring is meticuluous including wire loom, I bought a 30 amp voltage reducer from Amazon with instructions on it and guy selling them included own instructions also so heres the instructions on reducer red wire fused 15 amp 48 volt positive input yellow wire 12 volt output black wire public ground fine red wire 48 volt output to electric door locks output can not be treated as input or immediate damage to module will result. ( Note reducer does have 48 volt negative wire also so that a no brainer but instructions on reeucer dont list it.) Now heres the kicker seller included own instructions saying he hooks his up like this 48 volt positive and 48 volt output wire together as this is remote turn on wire and run thes to 48 volt keyed (small post on solenoid) meaning 0 volts when key off 48 volts when key on there by shutting off reducer when key off and the negative 48 volt to B- on controller and the 12 volt positive and 12 volt negative is a no brainer I had cart stripped to run harness fuse blocks etc so i finished all this up and put old batteries back in for a pre-test and everything worked so I cleaned up and put brand new set batteries in and put back together to cut light templates out well now the reducer blows fuses everytime I turn key on only on 48 volt side so the question is WHY I do believe you can use solenoid like that but why would it work with old batteries and only change was new batteries. And for the record I unhooked reducer via quick disconnects and tested cart itself all good even OBC and runs like a charm even charger kicks on and off like should.