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  #1  
Old 03-01-2004, 09:52 AM
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92 400E Aux fan wiring

I was doing some work on my auxiliar fan cuircuit and noticed that the schematics that I have did not match the wiring on the car. In the schematic (below, if it loads OK) the fuse F22 (blade fuse next to brake reservoir) has red wires on both sides and it fuses the high current supply to the aux fan relay K9 but on the car the fuse F22 has black and violet wires on both sides and it fuses relay 87a output to the preresistor (where the hand is). My questions are:

1. Is my car the only one wired wrong?, or wrong schematics? Can other 400E/500E owners check their aux fan, blade fuse wires?
2. why protect this low fan speed (for A/C) circuit while the other fast speed fan (high coolant temperature) cuircuit appears to be unprotected?

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92 400E Aux fan wiring-aux1.jpg  
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Old 03-01-2004, 08:26 PM
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What color wires does the resistor have?
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Old 03-02-2004, 08:30 AM
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pre-resistor wiring is as in schematic

pesuazo - The wiring on resistor color is as in schematic. Black/violet on one side and black/white on the other.
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Old 03-02-2004, 01:22 PM
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So you have the resistor AND the fuse connected to the auxiliary fan (in series)?

Actual pictures can make a world of difference.
Do not be surprised about the color wire, I have found the same thing in my car. The schematic shows one color wire and the car has a different color wire. The biggest concern is the gauge and the routing of the wire.
I think you may be mis-identifying the fuse F22.
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Old 03-02-2004, 01:45 PM
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I may be misidentifying the fuse number but I am few things very sure and confirmed by testing and checking with DMM.

Things I am sure of: There is a fuse on the slow speed side of fan. The blade fuse at the brake fluid reservoir is between the relay K9 (87a marked 1) and resistor. At least this portion of the schematic is wrong or I have a wrong wiring.

If there is a fuse on the red, power supply wire I cannot locate it.
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Old 03-02-2004, 02:25 PM
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I will try to rationalize the circuit set up.
The current coming from output 87a should be lower than the current coming from 87b (due to resistor in series). Experience tells me the wire thickness from 87a to resistor is thinner than the wire coming from 87b. IF the resistor was to fail (short circuit) the current draw would be too large for the wire (from 87a) overheating the wire and creating a fire hazard. The fuse would act as a protective device for the wire coming from 87a to resistor.
Since the wire coming from 87b is thick enough it will be able to hold all the current without problems.
For now that is the only explanation I can think of. I hope it helps.

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