I am from Ohio, but currently I am living in New Zealand. I must be part of an unknowing exchange program with your NZ caller from last week. I take advantage of your website each week to get my weekly fix of CarTalk 
I purchased a 1990 Honda Acura Legend and it has a strange problem with the speedometer. I can drive the car for about 5 kilometers and then the speedometer starts jumping and/or just goes straight to zero. This is where it gets interesting…I have found that sometimes (not always), I can make the speedometer work correctly as long as I do the following: With the windows up, press the up button of either the rear windows or the passenger window (Pressing the up button on the driver’s window never makes the speedometer work). When I release the up window button, the speedometer returns to zero.
Also, occasionally the electric locks will click to auto lock the doors and the speedometer will start working again. I cannot manually make the speedometer work by pressing the lock/unlock buttons.
I spoke with the previous owner and his mechanic replaced the speedometer cluster and the VSS (Vehicle Speed Sensor on the transmission).
Do you have any idea what needs to be replaced to get the speedometer working correctly (or any suggestions as how to do some testing to identify the problem)?
Thanks,
Jerry
PS: None of my cars back in the States have this problem. One assumption could be that this problem is caused by the steering wheel being on the wrong side of the car. I thought I would get your opinion before I moved the steering wheel to the left side
I have a 1993 Honda Civic which I purchased new, and about a year ago my speedometer started doing the same thing. Apparently this is pretty common with Hondas, according to my mechanic. The only solution is to replace the speedometer head. What has happened is that the circuit board inside that head has gone bad. This head can be replaced individually in your cluster. Google “speedometer repair” and you will find many places that offer this service and quick turnaround.
As for your other problems with power windows - my car doesn’t have this feature, so I am not sure if this is related. My solution was to buy a GPS unit, which not only tracks the mileage, but also acts as a speedometer. I may still cough up the $200 to replace that speedometer head, however - as it is a pain to constantly have to attach and remove the GPS unit from the windshield.
I have a Honda Accord 1994 with the same problem. I have replaced the speed sensor on the transmission and I still have this speedometer on and off. Your sensor is seding the correct signal to the ECU that is why you do not see the engine check light on but there seems to be a bad connection in the wiring between the speed gauge and the speed sensor. I could not locate it so I gave up fixing it. You may have to find a way to drive safely without it. Sorry.