OK, doing this from memory..so if I omit a step, or the Dodge is slightly different, you should still be able to figure it out.
The Corvette Vacuum Door system consists of two separate Vacuum circuits, The Control circuit, and The motor actuator circuit.
It starts at the manifold, where it goes to a Vacuum Filter, and a one-way Check Valve.
From there it Tee's off, One side to a Vacuum Buffer tank (usually in the nose) , and the other goes to the Bypass switch, (a Vacuum valve that cuts vacuum to the switch allowing the headlights to fail safe "Open") and from there, to the vacuum port on the light switch..
From there, It goes to the Vacuum Relay (s) up front..Works like an electrical relay, except it's controlled by vacuum and directs vacuum and static pressure to the door actuator motors.
From there, The control vacuum terminates at the relay control port (coil on an Electrical relay) Vacuum on this relay directs Vacuum from the buffer tank to the Relay Vacuum port (Contact on an Electrical relay) and the other side is Static air pressure..
When activated..the Vacuum relay valve travels between static air and Vacuum pressure to the Vacuum motors..On a Vette , If I remember correctly, It takes Vacuum to close, and Static pressure to open..
The Vacuum motors are a large vacuum canister, with a set of ports on them , one for Vacuum from the relay, and the other for static pressure from the relay, with the diaphragm in the middle..It moves by varying the pressure / Vacuum between the diaphragm.
To trouble shoot, get a hand vacuum pump and a handful of vacuum caps of different sizes..
Pull the control Vacuum line from the manifold check valve , and insert your hand Vac pump..
Next at the light switch, on the output side of the Vacuum switch, going to the vacuum relay(s), pull and plug that port..Pump up the hand vac gauge, to about 15 In Hg..and let it sit..It should hold vacuum..(at least 5 minutes..)
If it leaks, check the switch and bypass switch and the hoses..repair as needed..Move on to the line going from the switch to the relay..same applies here..
If that checks good, attach the hand Vacuum pump to the relay control port..it too should hold vacuum..If not replace the relay..
That should be the total of the control vacuum circuit, if good, hook it all back up and move on to the Vacuum Motor Actuator circuit..
Locate the Buffer tank, it should have 3 ports on it (looks like a standard vacuum tank) locate the two lines going to the vacuum relay (s) pull those at the relay and plug them..
Pull the hose going to the manifold filter and check valve, insert your Hand Vacuum pump..Pump it down to about 20 to 25 In Hg..and hold,
It should hold vacuum at Least 5 to 15 minutes..(in a perfect world, forever..) If it won't hold Vacuum, or has a bad leak rate, move your plugs to the tank canister itself.., and plug..then pump it down at the TANK, and see if it holds vacuum..
If not, you have a bad tank..(they like to rust out..) repair or replace as needed..If it holds Vacuum. test each hose to and from it..for rots or splits..
If good, go to the Vacuum relay, the center port is input from the Vacuum tank, the large port is vacuum to the actuator motor..pull and plug the actuator motor line and pump the center port down to about 15 In Hg..and hold..
If it leaks, replace the relay (s) If good, move on to the Motor actuator..the large hose is vacuum, place your pump here, pump down to about 15 inHg with the static side of the motor open to air..and see what movement you have..
test from both closed and open positions..If you CAN NOT get any movement and have a major leak rate you have a blown motor, replace it..do the same on the other door..
If that is good, from there hook everything back up and backtrack with the vacuum pump actuating components as you go, where it quits working, is where you need to replace the component..
The first thing to check is the filter and check valve at the manifold..they fail regulary..and be sure there is NO( water in the system..
That's about all I can remember..I'll try and pull up the diagram today..should you need it..