As stated in the test ..you leave the sensor hooked up..you simply peel back the insulation sleeves on the spade connectors so you can see the bare spade connectors at the end of the pigtail wires and you jumper across there ..I use a screwdriver blade, but you can use anything..it is just a jumper test. You do not unplug anything.

Alright. I will redo that tomorrow - its late here and heading away early tomorrow for the weekend. I will post my results sometime sunday. Thanks for your help.

OK
You may also want to check to see what they have done at this resistor..

http://catalog.peachparts.com/RenderScriptTemplate.epc?_cmd=epccat_VehicleAAA&cookieID=2EI1B4MYE2FA1DDHNT&yearid=1986%40%401986&ma keid=MB%40%40MB&modelid=300%2DE%2D002%40%40300E&catid=G%40%40Cooling+System&mode=PA&subcatid=G5040@@ Aux%2E+Fan+Resistor&source=www.peachparts.com&clientid=catalog.mercedesshop

This is behind the driver headlamp area and it is in the aux fan circuit..they burn the wires off and that will stop the fans.

They may have jumpered that section.
If those wires are intact, take a jumper from bat + and bring it over to each side of that resistor...one side should give you high fan and the other will be low fan...if YES, then fans/circuit are verified as OK from the resistor downstream, so your problem is upstream feed from the resistor.
I can guide you thru that after I have those test results .

aux. fan
 

No resister near headlight. I have a two prong plug going directly into the fan. I dissconected the plug and the fan ran on high speed, When tested directly from the battery. This is a 1986 300e with single fan. I am thinking of puting a temp sencer at the thermostat inlet and haveing the fan come on from there. I can't trace the wires back from wheel well to the fuse box. No blue wire near the thermostat. Could the differance be that this is a 1990 motor in a 1986 car?

<<Could the differance be that this is a 1990 motor in a 1986 car?
>>

That is exactly what you have..the aux fan circuits had been modified from a standard temp sensor circuit to a Thermistor sensor [ the blu sensor] in 1988.
So, they are not compatable b/c the later one works off the temp input of the ACC panel..You do not have that type on the '86 and the circuitry ..

So, yes..a simple relay and switch type sensor will do the job.
What have you got for a tap hole at the termo housing for mounting a sensor??

Here are a couple of things you may want to know.

Just b/c you have the single fan, you still have two speeds [ that is what the resistor is for].
If you have a/c working, then you are going to want the low fan circuit to also work.
I think they just did not know how these two circuits worked, so they eliminated the Resistor ...

But, I have a schematic for both.

You can also go with a cabin switch as a precaution..many guys do that just to have manual control in traffic, towing, etc.....they just run a jumper wire infrom the a/c high side sw .... so the system is still stock, but you have that over-ride when needed..

Thanks Athur that will help me. I am in the heating air conditioning business and can get strap on sensers for piping. I am going to get a stap on unit and install it on the space between the thermostat and the engin. Thinking 80 degree C for the on temp. This would bring the fan on high speed, or should I go 90 on and 80 off? Could you post a simple wiring diagram for this setup? I would like it to run only when the key is on. Please let me know what you think of that idea. A/C not working, not to concerned here in the great white north. By the way the wires on the air conditioner are loose and I was thinkig of bypassing it?

Well, the reason I asked about a tap at the termo is b/c Benz uses a 100C to ground sensor for some models...you could just screw that in and run the ground wire from a relay coil side to that sensor..then use relay contactor side to trigger a full 12v to the Fan..that will give you High Fan only..
I would even use the relay that is already there , behind the fuse box.
That way you alreardy have the relay and fused circuit..just need a sensor.

I am not at the car right now, but I had the cover off the panel up from the fuses and see more than one relay in there. Which one is for the fan? Are you saying that if I went from my sensor to ground I would activate the high speed fan?

You still have the old motor???

That had a 3 wire switch for the high fan ..think it was on the head.
Anyway, according to that schematic [ pre-88]..the fuse is "D" and the relay is K9
That wire to the sensor is br/gy..look for that wire . if you ground it, the fan will come ON if they left the relay and fuse intact.
try it and let me know

if that is the case , all you have to do is put a sensor in there that grounds when temp is high [ the benz one for 190 is 100c, the E is 105...] and hook that wire to it....or bring that wire to a cabin sw and ground the other side of the sw.

Here is what was on the old engine

http://catalog.peachparts.com/RenderScriptTemplate.epc?_cmd=epccat_VehicleAAA&cookieID=2EI1B4MYE2FD0ZMMN4&yearid=1986%40%401986&ma keid=MB%40%40MB%40%40X&modelid=300%2DE%2D002%40%40300E&catid=G%40%40Cooling+System&mode=PA&subcatid= G5045@@Engine+Temp%2E+Sensor&source=www.peachparts.com&clientid=catalog.mercedesshop

..but if you do not have that one, I would use the 190 one instead..b/c it is 100C and that would help the a/c as you will only have the single speed now.. The RED one:

http://catalog.peachparts.com/RenderScriptTemplate.epc?_cmd=epccat_VehicleAAA&cookieID=2EI1B4MYE2FD0ZYXGJ&yearid=1987%40%401987&ma keid=MB%40%40MB%40%40X&modelid=190%2DE%2D003%40%40190E++2%2E3+16%2DValve&catid=G%40%40Cooling+System &mode=PA&subcatid=G5030@@Auxiliary+Fan+Switch&source=www.peachparts.com&clientid=catalog.mercedessho p

Thanks Arthur : I will check this out first thing in the morning. You have been a great help.
Steve:D

Tried the second test and definitely no go. Before doing that, I caught your post and investigated the area. I found the resistor. Its in a tight spot so I was not able to do much this evening. Poking around further, I found the pigtail that "should" have been connected to the wires I photoed earlier. Unfortunately, the blac/white wire was broken off. I tried to do a quick patch to try and restore continuity but was mostly unsuccessful. Now that I know where the wires are supposed to go, I will get them fixed up tommorrow eve then rerun the earlier tests.

Looks like I have some patching to do first then I will rerun the tests. Thanks for pointing me in the right direction. The PO had tucked the broken pigtail way under the headland in such a way I thought it was part of the lighting circuit. I will get that all patched up the get back with the results.

Any suggestions on the wire gauge to repair with? 16?

Yeah.........

Pulled the wires ffrom the fans out of the front end of the car to get access. Checked them for continuity and resistance and got nothing. Tried hotwiring the black/white to a hot terminal and connected the ground and not even a hint of life. Not sounding good so far.

I did connect the wires back up with the pigtail I found yesterday and ran the tests again in case I was missing something and no response from the fans.

The motors turn freely with no grinding feeling. My plan is to pull the Aux fan assembly off this weekend and trace the wires right to each motor and check continuity. any other suggestions welcome

Once you get the fans off, bring direct 12v battery jumper to each to verify the motors and we can work from there back..that will be the best way as someone has played around and I have no way of knowing how they were thinking. [ if they were ]
It will not be hard to get it back where it belongs, we will just work backwards in this case. These are always fun.

After seeing the nomex, I am surprised they did not throw in a 2X4 and nails also...

Well. Off the fans will come. In looking at the assembly, there are several bolts around the sides. Due to the limited access in front of the radiator, must I pull the radiator to get this assembly off? or can I sneak it through the front structure of the car?