I have a 1988 300E that developed the problem of having the Auxiliary fan staying on after the car is shut off. This went on for over 2 hours until I decided to remove the fuse to shut it off. Any ideas on what caused this intitial problem?
It also developed a secondary problem when I went to start it the following day. It starts but shuts off within 5 seconds after releasing the starter with the ignition key. It will start this way again time after time with no delay so my assumption is that is not a fuel pump issue unless there is a secondary circuit that initiates after the start cycle.
Any help would be greatly appreciated.

Most likely a bad aux fan relay (2) on that car.

Try removing 1 relay at a time & see which one is the problem.

They are in the rear section of the fuse box at positions "B" & "C".

That letter is inked on the plug connector beneath each relay.

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Thank you for the suggestion on the relays. Do you think this is also the reason for the car not continuing to run after the starter stops?

That sensor will cause the fan to run if it switches on so I wonder if you may not have a short in the wires/harness that is extensive enough to cause your other problems.

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1986 300E 220,000 miles+ transmission impossible
(Now waiting under a bridge in order to become one)

Reading your M103 duty cycle:
http://www.peachparts.com/shopforum/831799-post13.html
http://www.peachparts.com/shopforum/831807-post14.html

1984 300d Turbo 140,000
Tap The Tops Of Relay To Release The Contacts, Had Hi Blower Relay On When Ign Was Off, New Relay $12.00 Auto Parts Store, No 2 Low Fuel Miles 13 Went To 16 Mpg V6 Engine Olds , Relay For Carb Heater Was Staying On, The 12 Volt Elect Heater Under Carb, Relay $12.00 5 Min Done, Check Mileage 3-4 Times Do Not Use Gas Gage Fill Tank Log Miles And Fill Again Same No Pump Same Station
Replace Fuel Filter If Using Power Up Hills Engine Slows

could this also be a solution for a 94 E420?

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