New electric jack

[Craigrrr]

Bought an electric jack 3500 # Haulmaster has the 2 side led lights and a 5.5 " drop leg. I do have a wire at the tongue labeled elect. jack So I ground off the paint on jack and trailer so to have a good ground and even used the star washers provided to give that extra bite. Now I hooked up the jack wire to the tm tongue wire labeled elec. jack, the lights are only dim and jack does nothing, so I chk for power at that wire, I have 8.6 volts dc. and I have the trailer pluged into shore power, but I did not have the battery switch on. So then I checked the 7 pin bargman connector on the tm , I have 14.1 vdc at that point so I plugged the jack wire into that and the lights are bright and the jack works fine. So my question is this...Why would the wire labeled elec. jack only have 8.6 volts?