Anyone have any experience with a cruise control system in the early 240s?

I just grabbed a whole unit out of a '80 that was in the junk yard. (Same car that it will be going into. It was even a manual transmission like mine.)

I got the speedo out of the car as well. It looks like (not 100% sure) that I can take the sensor out of it and put it in mine. At least, I sure hope so. (Donor car was a sedan, mine is a wagon.)

Anyway, I don't know much about these early cruise control systems.

Basic questions:

How well does the system work?

What are common failure points?

Anything I can do to the system to improve it, or prevent any issues while the system is out of the car?

Just how important will my speedo's accuracy be? (The needle bounces a bit.)

If anyone has any schematics that show how this mess is suppose to be hooked up and could give me a few details about the wiring, I'd appreciate it. (I didn't take notes, as I had to pull the thing quickly.)

Thanks as always.
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If you listen to the radio in Portland, OR, you may know me as 'Portland's Favorite Soul Brother!'

I repaired this unit on my 82 242 . It took a look at the green book I got from Volvo. The cruse book and electrical book is around $ 40. and I think well worth it. Dana stopped making this unit in the early 90s and the only parts are hard to find. I also read that when the servo unit shorts out it takes the computer with it. When working the unit works pretty well but you have to get the spedo cable working smoothly and not jumping. The cable that goes to the throttle can be changed out to fit your car , May have to look at the pick and pull for the correct length. To me it was worth the effort to repair this system but the green books are needed . Not hard just a lot of parts to install.

Eck 242 81

Does 80 use the "Dayna" system or is there an earlier type? I have the Dayna system on my 84. It works Ok, but it is not as accurate as computer newer types. Mine sets a little faster then I am actually going. There is an ajustment for that but I have never gotten it perfect.
The main problem is that it is driven by engine vacuum. A real problem for me because mine is on a turbo. When it goes up hill the turbo boost kills the cruise. It is probably OK on a NA car.
If you took note of where all the parts were off the parts car you should have no problems installing it. The throttle cable is intake manifold specific. There are different length cables depending on the intake and where the vacuum actuator is mounted. IF your car is identical to the donor you should have no problems.
Both Bentley and Haynes have wiring diagrams for this cruise. At least on the 81 to 85 speedos you can just add the pickup to your own. If your speedo is jumping because of a bad cable or speedo drive it would affect the cruise.