BMW Repair: BMW Windows Stop Working, bmw windows, volt ohm meter

Question
I just recently purchased a 1994 BMW 540i my windows work with the key in position 2 but after the car has been running for around 3 to 4 mins. the windows quit working.  The only way to roll them down is to pull over bring the key back to position 2 adjust the windows down and start her up again and off i go.  Some say it may be the regulators which may need lubing especially since the car has been sitting for a little while (5-6 months or so).  If I mess with the switches wile driving sometimes they'll decide to work and sometimes they won't.  Could I possibly have dirty contact in the switch area?  Does my battery need checked?  What does anyone suggest?  

Answer
Deb, the E34 (chassis code for your 5 series) is not my area of expertise. I can give you some things to check though. If none of the windows work then your problem in not all four wind. regualtors. If you are able to play with the switch and the windows start to work again the problem is most likely the switches. I you want to do a little diagnosis (never hurt anyone) then buy a good Digital Volt-Ohm meter and a repair manual with a good wiring diagram. Visually check the fuse responsible for power to the window circuit and make sure you have Good Voltage going to and through it. Remove the window switches and make sure they have good power and ground according to the diagram. Check these when the windows work and when they don't and see if there is any difference. If there is no diffence then replace the switch or borrow one from another E34. Or you can pay a quality technician to do it. Hope this helps
-Evan