I installed an aux fan from a 1988 560SEL, and it worked fine when I tested it, but today it didn't turn on. I tried jumping the temp switch but nothing, I then tested my old fan which was working and it didn't work with the jumped wires either. Fuse #10 looks fine and my back up lights work which are on the same fuse as the fan. This leads me to think that it's the relay.

I found out while searching for the relay location that the older model W126s had two speed fans. Could that be the reason my relay went out? Thanks

__________________
'81 300SD

Will your air con switch have to be on? And yes it allso as two relays for the aux fan . Google search, and on the search page click on immages top right put your question in the box click on it. I put [ mercedes auxhiliary relay location. ]

I found out that the aux fan relay for my car is in slot B. I placed a spare relay that I had into slot B and still no luck, then I noticed that one of the plugs got toasted(see pic). I then hooked up the original fan with a good relay pulled from another slot and still no fan with the jumped wires. Even though the fuse looked good I replaced it and I'm still not getting any juice to the fan. Did trying out that larger fan do some serious damage to the circuit?

Attached Thumbnails

 

__________________
'81 300SD

I took a multi meter to the blue/brown wire that goes to the temp switch and got 12 volts. When I installed my jumper wire to connect the blue/brown to the brown wire, I got a reading of no voltage on the jumper. The fan works when I run power straight from the battery. I tried running a jumper wire straight from the blue/brown wire to the positive fan plug and grounded the negative plug to the battery, with no luck. I tested the blue/brown wire again and it came up 12 volts, so I think that my relay and fuse must still be good. I have no idea what could be wrong. Jumping the blue/brown and brown wires has always worked before.

__________________
'81 300SD

What was your outcome? Having the same issue with my 84

Sent from my SM-G892A using Tapatalk

I know someone will chime in with better details but a brown wire any where in the car is always a ground .

If it has a colored stripe it's a switched ground .

I'd begin by testing the plug to the fan to see if power is present with the key on and HVAC set to AC and MAX to begin with .

Detail what color wires are on the plug at the fan .

Do not use a meter for these tests, use a lamp as you need to lightly load the circuit for real world testing .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

On the W123, the aux fan wire connector, below-left of the radiator, is notorious for giving birth to bad connections. If the W126 has the same connector, which I suspect it does, that is most likely the culprit. It's the half of the connector that belongs to the chassis wiring harness and not the fan. If you can't find a connector replacement, you may have to delete both sides and wire nut them together. BTW, the brown wire isn't a traditional ground in that it can't be mis-wired. If it is, the fan will just spin backwards.

__________________

Don't Chrome them; polish them