Electric window lifts

[worzel]

Hi

Apologies for posting it here but it is Lotus related (and I never received a reply from the Excel owners forum).
Why does the window lift motor on my 89 Excel only operate for a few days at a time.? I've lost count of the number of times I've stripped the motor to find that where the brushes make contact with the brass/copper internals that a dark "ring" appears that apparently prevents current flow.

Cleaning off this ring with thinners immediately restores power- but only for a few days.

Substituting another known perfect motor produces the same problem so it's unlikely that the actual motor is the problem. If so any ideas on this one- I'm pretty sure the connector plug is not the problem. Is it possible that (in some mysterious way) the switch is the root cause and if so any ideas on what to look for. Incidentally it's not caused by water ingress- where the switches are water never reaches.

The window circuit doesn't have any "black boxes/mysterious electronic bits in it by the way.

Regards

John

[type36lotus]

Have both motors been rebuilt? Possibly with the incorrect type of brushes? Is the dark ring greasy? If so it could simply be grease burning up on the commutator.