Can i lower the seat height of my 2006 roadliner?

Ouch... this sounds serious... maybe it time to visit your local Yammer dealer!! This is not complicated, but a very involved and time consuming repair!!

The dipstick on all the Yamaha XV1900 models is under the drivers seat. To check the level, be sure the bike is in an upright position (off the sidestand) then remove dipstick, wipe, and reinsert WITHOUT screwing it in. Just dip it. Oil level should be between the upper and lower marks. Yamaha offers free .pdf owners manuals if you don't have one to access here: https://www.yamahamotorsports.com/motorsports/owners-manuals

Below the tank there should be about 4 bolts holding the tank to the frame, loosen then and lift the tank enough from seat side, you should be able to access the wiring and plugs.