Background: After putting up with intermittently functioning cruise control for a couple of months after I bought my 300D, I purchased a remanufactured Programma amplifier, installed it and the next day enjoyed flawlessly functioning cruise control on the 500-mile drive from Houston to Tulsa. It engaged, disengaged, held perfect speed without any jerkiness, accelerated, decelerated, etc., all without any problems whatsoever. We stopped and turned the car off at least a couple of times for lunch, etc. and the cruise worked each time I restarted the car.

About an hour after I turned the car off in Tulsa I went outside, started it and took a short highway drive to a friend's house. Wanting to enjoy the pleasure that is fully functional cruise control, I tried to engage it and, to my utter chagrin, saw that it wouldn't hold steady speed, accelerated without my telling it to, disengaged on its own, etc. I didn't have time to mess with it then so I just tried to forget about it.

The day after that, I set off on another long trip - this time to Colorado. Well, I tried the cruise at various times throughout the three week trip and not once could I get it to engage AT ALL - not even intermittently as it did in Tulsa.

My question: I'm working through the test procedures from GDL and am having trouble understanding "Step 3" of the test, which they say is "CRITICAL":

Use a current-limited 13.8 Vdc Power Supply with a series DC Ammeter. Connect between pins 4 and 5 of the actuator plug.

What exactly is a "current-limited 13.8 Vdc Power Supply"? Does the car's battery qualify? I don't want to hook it up to something and make the problem even more expensive to fix.

Also, what is a "series DC Ammeter"? Will my little multimeter work for this test, or do I need to go buy some fancy device that I might never use again?

Finally, while I'm committed to working through the published test procedures, does anyone have a guess as to why the cruise would work perfectly one day with a brand new amplifier, and then stop working reliably later that day, and then stop working altogether the next day?