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  #1  
Old 09-27-2011, 11:19 PM
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Join Date: May 2010
Posts: 71
Checking auxiliary fan wiring/relay on an M117

How can I check if my auxiliary wiring/relay is working?
As I understand fan switch supposed to turn on the auxiliary fan when water temperature hits 100 degrees C. Since the fan switch got a single wire I assume that it just makes a ground connection once the switch heats up. So I tried to just ground the wire directly to see if the fan turns on or not, but nothing happened. Is there some other condition that has to be met for the auxiliary fan to turn on or is that a sign that there is something wrong with my auxiliary fan relay or wiring?

P.S. Where is the auxiliary fan relay located?
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Old 09-28-2011, 09:33 AM
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Join Date: May 2006
Location: Atlanta, GA
Posts: 591
Do you have a W108/109/111 model car? If so, auxiliary relay is one of the round relays to the front right of the engine just behind where the ECU is mounted. I had an old post on the location of my fuel pump relay and had a picture of the MB workshop manual that showed all the relays in that position. You may want to search for it.

I "shorted" my auxiliary switch by adding a ground wire under the ground connection of the relay. That activates the current to the fan.

Good luck,

Bert
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Old 09-28-2011, 03:22 PM
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Join Date: May 2010
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Quote:
Originally Posted by sjefke View Post
Do you have a W108/109/111 model car? If so, auxiliary relay is one of the round relays to the front right of the engine just behind where the ECU is mounted. I had an old post on the location of my fuel pump relay and had a picture of the MB workshop manual that showed all the relays in that position. You may want to search for it.

I "shorted" my auxiliary switch by adding a ground wire under the ground connection of the relay. That activates the current to the fan.

Good luck,

Bert
I got a W108. Thanks for the suggestion, I'll give that a try.
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