Labor day Results
 

OK, it's labor day weekend and what better to do than repair may blower motor on the E420?

Here is the data

1. yellow wire at the firewall form the controller reads ~2-5 volts. ie controller is ok

2. Red wire at the firewall from the controller is not grounded and does not read 12 V as it should.

3. Motor doesn't run when blue wire is grounded (of course, based on #2)

4. Motor does run when +12V is supplied to the red side at the motor AND blue side is grounded

5. Motor does not run when +12V is supplied to the red side at the motor AND blue side is connected to regulator

My conclusion, I need a new regulator and possibly a climate control unit; blower motor is OK.

My question, is there any way to diagnose why the red wire from the controller is not reading 12V?

The good news, most parts are out of the car, hood closed and it looks fine and it's driveable!


Thanks for all the help...

#2 and 4 indicates you have a bad power feed fuse.

Fuse harness
 

No voltage at the fuse. Remember I had overheating on the fuse harness. So, with no 12 Volt at the fuse link, I traced this fuse cable down below the brake booster and it disappears from there. Any suggestions?

One thought is to bring a new +12 leg and abandon the old fuse cable. Would this work?

Is there a better option to repair the +12 lead at the fuse?

Since I have to replace the regulator, is there any difference in the regulator itself between the cabin filter-fitted and the non-cabin filter-fitted parts, other than the shape of the heat sink, which doesn't need to be replaced? This E420 has a cabin filter.

By the way, driving the car without all the insulation by the firewall allows some engine sound into the cabin. First I thought the blower was back (which couldn't be). Interesting how much sound insulation you get from all this rubber and plastic at the firewall.

Thanks for taking the time to help

<<One thought is to bring a new +12 leg and abandon the old fuse cable. Would this work?>>

You could , but you want it AFTER the ignition switch.
I would certainly do a little further search myself, if for no other reason than the possibility of shorting circuits with the old feed.

Does the fan operate if you jumper bat+ to the fuse holder????????????

Not Fixed yet
 

The fuse holder directly goes to the red wire at the motor on one end. The other end I traced to go inside the car under the steering wheel and into a wrapped bundle that I would rather not mess with. I think it goes to a +12 V source past the ignition switch. So, in answer to your question, yes it will run.

Any other thoughts? Anyone?