Overdrive unlocking on level ground and down hills

[84RabbitGTI]

Well, I am finally having a problem with the overdrive. It has been one reliable part of the car until now. I have the manual and will go through the checks of the electrical setup, but thought someone else here might have had this happen to them and could share the solution.
When I am driving the car on level ground or going down a hill the overdrive dis-engages as if I hit the kick-down switch. It goes back into freewheel mode. You can hear something going on under the floor where the trans is: electrical or mechanical, I'm not sure which, but you can hear snapping, like a spark or something clicking into place, not sure which.
When the car is heading up hill, the unit works pretty much like normal.
Thanks for any advice.

[kaiserfrazerlibrary]

From my past experience and the clues you give, it sounds like your first stop should be to check the wiring from the kick-down switch and the kick-down switch itself.  It can deteriorate with age and may be shorting out which fools the system into thinking the switch  is being engaged to cut the overdrive out.

The cars are now over 60 years old, and electric parts will deteriorate even on the shelf in some cases so strange things like this can happen.

[Fid]

I concur with that. It sounds like a loose or worn wire touching ground some where.

[84RabbitGTI]

Ok, I'm going to work on it tonight. I'll let you know, thanks!

[84RabbitGTI]

I just got back from under my car. My wiring is in first class condition. I replaced the original with a McBride wire harness in 2008. The terminals are clean and tight.  It might be the kickdown switch itself, I suppose as it is the original, but still looks good and clean. I rarely use it while driving the car. I suspect it is one of the relays or the solenoid on the transmission.  I'll have to test them to see after I do the electrical continuity tests to make sure all the electricity goes where it should.  Thanks.