the o.e. testing states for the 3 pin connector harness side: black wire should have continuity to ground under all conditions. yellow, ignition switch on should have battery voltage (12V) to ground. orange, ignition switch on should have 5 volts to ground.

 

Problem solved.
I **believe** I had two problems. About 3 years ago, my speedometer would work intermittently. I put in a speed sensor and it did not solve the problem. I let it go for 3 years because the cluster was too much money. Eventually during that time period, the speedometer did not register anything at all. I think during this time, and after pulling the connector out several times - this is where the connector went bad. Out of all the parts I checked, the connector was in the worst condition.
Recently, I checked all the wiring (thank everyone for the information here) and found it to be good. So I decided to put in another speed sensor and connector (ebay $18).
After installing that, I had the constant 15mph problem. Then I found the cost of gauge clusters to be a lot lower than 3 years ago, so I sprang for that - $45. After installing it - I was good to go.

Here are some pics I took - maybe they can help some others
Connector C133 - top right under the hood



Connector C429 - this is not easy to get to, and it was wrapped very tight. Unless someone has touched it, I don't think this is the cause of many problems. If you sit in your car and look at the number '7' on the tach, this connector is located about 4 inches behind that, and a very stubborn duct is in the way. You can see the connector from underneath the dash, but it has it's own obstructions and I did not want to work laying on my back.