You can go to radio shack and buy a male cig lighter plug w/ built in fuse. use a guage and figure which wire is the pos. and which is neg. Usually the striped wire is the pos. or red--depends on type of cig plug you get.
Go and get four plugs that are similar and wire the speakers of each vehicle to each plug. You will have to extend the speaker wires a little probably. PUt the other side of one of the plugs on the head unit for speakers.
Then just plug the speaker plug in and plug the cig lighter in and you should be ready.
If you want radio---if your antenna wire is long enough on each vehicle, that just slides in the ant. spot on your head unit. l
SgtDel
aka "Andy"
www.delbridge.net
1979 Big 10 383 stroker
1991 Blu 'Burb 3/4 ton 4x4