intermittant blower motor operation manual heater, a/c 450 sl 1977
 

This is driving me nuts! Need help! When motor is cold, blower moter works fine on all reostadt switch setting (low to high). After run (or during), (no blower used or switch on) the blower will not operate with switch on. When try next day with engine cold, works fine! Seems like electrical? resistance in wiring from motor to firewall? All fuses OK. Any relay to check, location? Any help appreiated. Abe G PS which pins on plug (removed from 450sl) on blowermotor for testing with 12 volt battery? If possible sketch or photo appreciated. ONe lead to pin (positive) and one to ground?