1970 Mark III Power Window Issues & Updates

Hi Bill,
I have just purchased a 1970 Continental Mark III with 139,000 miles on it. The car is in great condition visually, structurally, and runs beautifully. There is one problem, however, the power windows. When the car has been turned off and the engine is cold or when just starting to drive it, the power windows work fine, but after driving for a while and the engine gets hot the windows stop working. It is very frustrating to say the least. I’m not positive that the temperature of the engine is the culprit, but this is just my observation. Do you have any thoughts about what could be causing this? Have you heard any similar stories or do you know any fixes? Should I try to have someone locate the problem (which may be difficult because the windows work intermittently) or should I have the windows rewired? I know Mark III’s have been known to have some electrical issues, but this one has me stumped.
Thanks for any and all help!
Steve
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Hello Steve –
I have never heard of any reports of the power windows becoming non operative upon engine warm up but in this business we learn new things every day. The power windows share the same relay power source as the a/c- heater blower. At the time when the power windows stop working is the blower motor inoperative as well? If so the power window safety relay on the firewall behind the engine or the direct power supply to this relay from the battery is a strong suspect. If the blower remains operative at this time then the circuit for the power windows would need to be traced from the relay to the breaker panel and through to the drivers door switches. The above is the best way to approach this issue and at the same time be on the lookout for some unknown wiring alteration that a previous owner may have performed. Do not try to rewire the power window wiring. Always diagnose the actual problem first with the use of a correct wiring diagram and 12v test light. This circuit is actually not complicated but the wiring diagram is a necessity and will save you much time.
Sincerely,
Bill
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Hello Again Bill,
I emailed you recently about the power windows failing to function after the engine heats up in my 1970 Continental Mark III. Thank you very much for your response and sharing your knowledge of the car it really did help to locate the problem; I think it was the master power relay. It seems the master power relay was heating up, tripping and shutting down and then resetting itself later. I was able to clean up the original relay and rerouted it to the front of the engine bay in order to keep it cooler with more airflow in order to keep it working. After a long ride today and after the engine got hot the drivers side window still continues to work as does the A/C blower, but now the passenger window is not functioning even after the car has cooled down (unlike before). I do here a slight click when the switch for the passenger side window is depressed. Does this still sound like a relay problem to you? Do I need a completely new relay? Or does it seem to now be a window motor problem? Or something else? If the relay was still tripping and shutting down from heat or all together bad, both windows and the A/C blower would fail right? What do you think?
Thanks Again
Steve
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Hi Steve –
Good that you were able to locate a problem area. However, these relays do not heat up and fail when heated as you describe and do not need to be relocated for cooling purposes if they are in good shape internally. If you have relocated yours to the front of the car somewhere you have also added several yards of resistance to the circuit in the form of extra wire. This extra resistance may or may not add to an unwanted drop in voltage. If you suspect that your relay has a further problem you can temporarily jump the necessary wires at the relay for diagnostic purposes only in order to prove if it is indeed faulty or not. You do not tell us where this “slight click noise” is coming from but if it is originating from inside the passenger door the motor could very well be faulty as you have suspected. I suggest that you read the recent July 2 reply to Alec. He has a similar problem with a 71 Mark and the diagnosis and basic testing suggestions in that blog reply should help you as well. To properly do this diagnosis, the correct wiring diagram is a must to have. If you do in fact need a motor we have excellent new ones as well as other p/w parts available for shipment.
Sincerely,
Bill
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Hi Bill,
Thanks for all your help with my problem. I think right now I may just have to change out the passenger side window motor. Hopefully, with everything you’ve said I will get this issue straightened out. Thanks Again for taking the time to answer my questions and help me find the problem with my Mark III. You’ve been a very big help!
Steve