Go ahead and Google "1982 Corvette - Speed Control Replacement" and you'll find the strings that I used, and probably my posts. I can't help you with the testing, voltage, etc. But, the root cause of most 1980-81 C3 cruise control failure is the transducer. Perhaps you are the minority and that is not the issue with yours so no promises. I was initially skeptical until the thing suddenly, and joyfully sprang to life when I first pushed the cruise control engagement button on the turn signal stalk after replacing it. The original owner of my car said that it hadn't worked in many years.
The replacement was a PIA, but satisfying. If I had smaller hands it would have been no problem. Getting it out is harder than reinstalling it, but take mental note of how it comes out through that small opening, so that the rebuilt one, that you buy for no more than $125 plus core, can go back in the same way. And, since the speedo cables go in/out of it, be sure to pull them out from their housing (they come out and go back in amazingly easy) and lube them with either a dry graphite lube or, as I did, a light lithium grease lube. So, you will kill two birds with one stone. My only advise is to hire it out if you have especially large hands due to the comparatively small space next to the windshield washer bottle. It is not an overly complex repair. And, be sure to have a small flex socket adapter ($6 and worth far more in this repair) because it's the only way to get the right angle to remove and replace the two bolts that hold the transducer in place. It is not an optional device in this case. It is a DIY repair that you will be glad that you did if you are at all mechanically inclined because it is fun to engage it on a nice long stretch during that occasional weekend getaway. Pay attention to the adjustment instructions that are included. Mine will accelerate and additional 4MPH using the stock adjustment, though I couldn't care less - but, if you do, the MPH calibration adjustment is straightforward using the adjustment screw/nut on top of the transducer. I spent the good part of a Saturday morning on mine, and I'm glad that I did. Btw, while had the patient on the table, I pulled back the protective black rubber accordion cover on the adjacent speedo servo and sprayed some silicone lubricant into the servo housing, just to lube things up. Hope this helps you and good luck. Dave
p.s. add a couple of pieces of duct tape along the inner edge of the fender before you start in order to protect the skin on your fingers in the tight space. You will know what I mean if you don't. Good luck and enjoy that speed control.
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