my 1990 420sel blower stopped blowing, replaced fuses, cleaned connections kicked the underside where its located and it came on a few times, but did not come on again by its self after turning off car. I turned my self into a pretzel to get it out, checked for baring play, no play, spins nice, cleaned it all out, attached 12 V battery, worked excellent, after installation worked great, then one day nothing, after a few miles, it comes on by it self works fine, next day nothing, is their something ell's I can check? im thinking a bad ground?

Also my dash lights at night come on then go off for no reason, then come back on when they want too just like the blower?. do you think this problem is connected?

I have had this car for 9 years, its never let me down, also I notice after I unlock the drivers side door, after driving down the road for 10 min i hear the other three door locks unlock themselves? Ideas anyone?

The blower intermittent operation is probably a bad blower motor. Have you cleaned the fuses and slid the push button HVAC control out and checked/wiggled wires for bad connections? Try jiggling the key a little to see if that affects anything. To know for sure, temporarily wire a bulb in place to the blower circuit. If the bulb stays lit
but the blower stops then it is the blower motor.

Instrument lights not working is often a bad/dirty dimmer/rheostat. Try turning it back and forth many times to see if it will self clean its contacts.

Good luck!!!

bad ground. They do break after oxidation.

check the connections to the blower resistor

or might be the resistor itself.

$$$$

More than likely the brushes are just worn down in the blower motor. Do as Sugar Bear suggested and test a light bulb in place of the blower motor. Use a high wattage bulb like a headlight to put some load on the blower transistor pack. If the bulb isn't dropping out, you can be rest assured the motor is your culprit.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

As mentioned above, the most likely cause of this behavior is the cluster rheostat. Super common issue. You can replace it, or you can just solder a short piece of wire across the terminals on it to bypass it. This will not be related to your blower issues since the circuits are not shared.

If you unlock the trunk or the passenger door, do all of the other locks immediately unlock? If so, you may have a wiring issue in the driver's door lock mechanism or the wiring harness. If not, you could potentially have a problem with the lock pump in the spare wheel well.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)