Complete Vacuum Routing for 390GT

My 1968 Cougar XR7 GT is almost restored after 6 years of 2 different restoration shops. (That’s an entirely different story) I am trying to find a correct vacuum routing for all the non-headlight system for the Cougar that is equipped as follows:

  • S code 390-GT
  • A/C
  • Automatic Transmission
  • Tilt away steering wheel
  • LA CA DSO 52
  • Speed Control
  • Power Disc Brakes
    *Equipped with TE emission system

I can find bits an pieces of the routing system but not a valid definitive answer from various items on the internet, I have see the the Mustang related materials for a 1968 but I am not sure that they are the same as the Cougar.

I believe I have confirmed I have a single distributor advance which is a Motorcraft DD-190.

Any input would be appreciated!!


I can see in the 1968 Lincoln Mercury Service Department Vacuum System Diagnosis Guide that the following vacuum lines are all tee-d together (A/C, Speed Control, Headlights and Tilt Away Wheel ) and end up plugging into the back of the manifold into the fitting C8OZ-9A474-B. This System Guide shows the automatic transmission going to the second studded port. As I have Power Brake Booster, the metal line attaches by screwing into this fitting as well.

My understanding is the air cleaner vacuum motor goes to the hollow stud on the drivers side of the Holley 600 CFM carburetor.

Is the C8OZ-9A474-B (2 male studs and screw in thread for the power brake booster) the proper rear fitting for this many vacuum accessories?

I have seen a 3 male studs vacuum fitting C8AZ-9A474-B for sale on the internet. I am not sure that 3 studded port fitting is correct for the 390-GT.

I have a handle on the front manifold fitting.

Found this in an article we have posted - redrawn or just cleaned up (can’t remember) and colored from a factory diagram but for a non-AC application. Can’t think of any differences that would be required for a AC car other than the vacuum sources for thew dash (under dash for heater, AC and tilt can

Unfortunately it shows the system in a diagram not showing the hard vacuum balancing lines and illustrating what this all looks like on a real engine. Sort of the difference between a regular wiring diagram and a wiring illustration like Ford and Mercury produced.

Also does not include the attachment for the PB where the flex line from the booster connects to a reinforced rubber line that connects to a long hard line that attaches to the rear vacuum block behind the carburetor that also services to connect the balance tube to the front vacuum block and vacuum nipples for allot of other attachments like for the automatic transmission, dash and so on.

Most of my pictures have the air cleaner in the way :frowning:

69 Assembly manuals might be more helpful in that department

Hope it helps for some of the connections

Here is a picture from the Mansfield site - they sell a fair amount of the parts and focus on FE related engine parts

I’ve seen many loaded 68 Cougars with 390s and they usually had the C6 vacuum line attached to the hollow carb stud. The front manifold fitting has one line to the temperature vacuum advanced valve and the other to the air cleaner. The three port rear manifold fitting would have the headlights and A/C on their own fitting then the tilt and speed sharing the remaining one. I saw once a small pamphlet from Jim (can’t remember last name) that showed all the vacuum routings. The shop manual misses stuff.

Most of the drawings like the one above and at mustang barn are not correct for a 390 GT with automatic transmission as the distributor vacuum advance should be single diaphragm unit. (This was the opinion of Tim O’Conner and Royce P.) There was a thread on this back in 2016 or 2015 I believe.

Motorcraft did not come into being until the 1973 model year so if you do have a Motorcraft distributor it would not be original. It could be a factory replacement and basically the same as the original Autolite part. I cannot speak to that, only that anything Motorcraft is not original on a 1968 Cougar. It may or may not have the same vacuum fittings on it as the original.

Randy Goodling
CCOA #95

CATHOUSE - Yes you are correct that the DD-190 is not original as the correct unit is an Autolite. The service part number is C5AZ-12370-A which the Motorcraft part replaces. The DD-190 looks exactly like the Autolite single diaphragm shown on the 428CJ website -

Eventually, I will hunt down a proper Autolite unit but the Motorcraft DD-190 should keep the motor running correctly.

I had to start with a lot of the expensive and unique parts to a GT 390 parts missing off the engine when purchased. Surprisingly there are not many concours correct pictures of a 1968 Cougar GT 390 motor on the internet so that is why I have many questions on the routing of various vacuum systems. Mustangs are similar but not exactly the same.

The good news is the rebuilt motor fired up recently with no problems. Hope to have her on the road by the end of the year, if not sooner. Still trying to sort out the tilt away system.

This drawing shows the dual advance distributor C80F-D, which apparently was used during the latter part of '68 model year on both manual transmission and automatic transmission. There is a different diagram for earlier cars that used the C70F-F single advance distributor. There is a TSB that advises the change, I don’t know the number off the top of my head.

Is it Ford TSB no. 1415 dated May 31, 1968?

Anybody have an opinion on the Scott Drake vacuum hose kits?

Thinking of redoing the mish-mash of odd length and off color vacuum hoses that reside atop my motor.