Tower Controller working all positions combined on a mid shift described a runway incursion event indicating coordination regarding closures were lacking.

Narrative

I was working the mid shift in the Tower with everything combined. Every night something different is closed. That night Runway XXL and Runway YY were closed as well as all the taxiways west of XXC. I was looking out at the airfield when I saw a lot of vehicles moving east on S Taxiway which was closed at the time. At the same time I was watching the couple aircraft left in the airspace being vectored for the visual to XXC. I watched the vehicles turn north on V then right on V4. I expected them to stop but It appeared at least 1 of them entered the active. I checked the ASDX and sure enough it showed a target on the active however this piece of equipment has been wrong in the past. A B717 checked in and I told him to continue because I had a vehicle issue. I tried to ascertain who was in that area by talking different airport vehicles on the frequency. I was not comfortable with the situation so I sent the B717 and the next aircraft over from XXC to XXR to land. Eventually I got an airport vehicle to go over to XXC and V4 and make sure there was nobody on the runway. He replied that they were clear and would hold short. I said they're holding short now but one vehicle was on the runway. He replied that one vehicle had gotten away from them. During this time we were trying to find out if XXC was supposed to be closed. They eventually closed XXC that night to work in that same area. There was no loss of separation since I sent the planes to a different runway so I didn't think it was something that had to be reported but after thinking about it and talking it over with a friend it was brought to my attention that it could still be considered a runway incursion and it was without doubt a unsafe situation. Recommendation; make sure that coordination is better as to what is closed and not closed.