The vacuum amplifier ports shown in the following image are identified as follows mostly as you have surmised:
(using the clocking here to specify)
- 12:00 - Manifold vacuum and/or reservoir vacuum
- 3:00 - Venturi signal vacuum
- 6:00 - EGR vacuum control (direct or via delay solenoid)
- 9:00 - Not used, for possible future use (may be blocked or open)
The small red opening separate from these is the air inlet vent. Inside is a foam filter, which is likely deteriorated after time.
NOTE: An additional separate port is adjacent to these ports on some later vacuum amplifiers and is capped.
The device next to the amplifier in the image is the EGR delay solenoid that blocks the vacuum signal to the EGR valve when activated by the EGR timer.
A molded plug with color stripe coded hoses connected to the ports and is secured by the screw in the middle:
Chrysler specified testing of the vacuum amplifier while on the running engine with the EGR system as shown in the following:
(from the 1978 service manual)
A basic bench test can be performed as follows:
1.) With the EGR vacuum control port (6:00) capped, apply a vacuum of 10-20 inches to the manifold vacuum port (12:00). The unit should hold a vacuum. Leakage of 1" or less at 10" in one minute is expected for a new unit. For a well used unit, 2-3" per minute might be seen. A rapid drop indicates a bad amplifier.
2.) With the EGR vacuum control port (6:00) capped, apply a vacuum of 10-20 inches to the venturi signal vacuum port (3:00). The unit should hold a vacuum. Leakage of 1" or less at 10" in one minute is expected for a new unit. For a well used unit, 2-3" per minute might be seen. A rapid drop indicates a bad amplifier.
3.) With the EGR vacuum control port (6:00) connected to a vacuum gauge, apply a vacuum of 10-20 inches to the manifold vacuum port (12:00). Some leakage to the vacuum gauge might occur until the setup stabilizes. Vacuum should hold at this point. Apply a small vacuum of 2-3" to the venturi signal vacuum port (3:00). The vacuum gauge connected to the EGR vacuum control port (6:00) should show the vacuum building. Stopping the venturi signal vacuum should stop the building vacuum. If these actions does not occur, a bad amplifier is indicated.
There were multiple variations of configuration uses and connections to the vacuum amplifier from 1974 - ~1985. Later configurations were more complex than earlier. Different engines had different configurations as well. California versus federal and/or Canada compounded the mix as well. In some applications, the vacuum amplifier was not used, and ported vacuum was used instead, so it is an alternative.
A federal vacuum amplifier and hose harness for a 1975 318:
A federal vacuum amplifier and hose harness for a 1984 360-4V light duty cycle truck:
Chrysler patented the vacuum amplifier under number 3818880. Following is the PDF from the US patent office:
