dual vacuum system C337

[cessnadriver]

HELLO ALL. Got a question for the group. Recently installed a G5 AI but needed the old vacuum AI to run the 400 navomatic. While behind the panel. I decided to remove as much old 1/4" rubber hosing as possible. So I installed 1/4" plastic tubing/ Now I have a vacuum DG, pilot's side and a Vacuum AI co-pilot's side. Hooked up the Garmin G5 and re-plumped the vacuum system. Went out and test flew my skymaster after the update. Wasn't too sure of my plumbing job, but had the G5 to give me airspeed , altitude and heading, just in case. Vacuum instruments spooled up just fine, BUT the vacuum gage ( the PSI side was not working), although the red buttons where IN. I cannot find a GOOD illustration of the skymaster's vacuum/instrument system. Some show the twin engine configuration BUT show four lines coming from the vacuum gage, mine has three, two to the vacuum manifold and one main to the AI/DG. Any suggestions?
Many thanks as usual.
Regards, BILLS