Check with your local boneyards to see if you can find another cruise servo. Anything from a late 70's to mid 80's Chevy, Buick, Pontiac, or Olds (I think Cadillac's cruise units were different) Either a midsize or full size car will work. Try to steer away from a diesel unit if you can. They can be adjusted to work decently on a gasoline engine, but why mess with it if you don't have to.
With the engine at idle, disconnect the vacuum going to the cruise, and cover the end with the pad of your thumb. If there's enough vacuum to firmly suction the hose to your thumb, there's enough vacuum to operate the cruise. Also, if you have a hand operated vacuum pump, check to see that the rubber diaphragm that controls the throttle will hold vacuum without leaking.
The backyard mechanic way for checking those diaphragms is to get a clean (at least one end of it!) piece of hose the same diameter as the inlet of the diaphragm. Use your mouth to produce a suction to pull the diaphragm to it's full position, then cap off the end of the tube with your tongue. It provides a good seal for you to check the unit. Leaks are almost always obvious. Slow leaks are harder to find this way, but in my cases has been unlikely. Either it holds vacuum for 30 second without losing it, or it wont hold any vacuum.
Hey, 28 mpg is way better than I thought your initial numbers would be. Congrats!
Found in the repair manual, in the section about adjusting ignition timing:
On 1975?77 HEI systems, the tachometer connects to the TACH terminal on the distributor and to a ground. For 1978 and later models, all tachometer connections are to the TACH terminal. Some tachometers must connect to the TACH terminal and to the positive battery terminal. Some tachometers won't work at all with HEI. Consult the tachometer manufacturer if the instructions supplied with the unit do not give the proper connection.
Never ground the HEI TACH terminal; serious system damage will result, including module burnout.
I was just trying to hook up a tach yesterday. I assumed I should run a line from the "Tach" terminal to the tach, and then ground the other terminal on the tach itself. It didn't work and I figured it was something bad about the tach, which I hacked out of a junkyard Camaro. Now I wonder if I did it wrong...
Well, the unplugged vacuum tee I found indeed belonged to the hose going to the cruise control. I put the tee back in and reconnected the cruise hose and now cruise works.
Next year I think I ought to replace every vacuum hose under the hood. While I'm at it maybe I can neaten it up, instead of dozens of short bits of hose and tees all over the place I could have a single vacuum hub and neatly routed hoses...there must be vacuum hubs, right?
In the meantime, back to chewing on that tachometer wire question...
I don't remember. I grabbed it at the junkyard probably at least a month ago and it sat around until I felt like working on it. I was in a hurry when I got it and I didn't take photos. It has 3 or 5 terminals, depending on whether or not two questionable things are terminals.
Maybe I'll try giving it 12v, ground, and tach signal...see if that works.
My windshield washer fluid squirter is not working. It's getting voltage when I operate the button. I tried applying power directly to it and it goes "tock." but doesn't seem to run. Is there anything else I can do besides replace it?
The washer pump is a mechanical one integrated into the wiper motor. If you can get your hands on a rebuilt motor at a decent price, that would be the best option. They used to sell rebuild kits for them, but I don't know if those kits are available anymore. On our Bonneville my dad had wired in a small electric pump to work, that will probably be the cheapest option.