Got a '92 300SD (with its exceptional wiring!). Had some problem with a short draining the battery. Haven't found it yet, but got it to go away. I think it may have been in F3f17 as I found removing that fuze got rid of the drain. Inspected the various things on that circuit, found nothing, put all back together again and it works. Turn signal/Hazard Warning are on that circuit. I know that's not a fix, but it has to fail again before I can find it.

Problem is, and has been since the beginning, that the left signal blinks fast with the stalk in any position (left, right, center) and the key in accessory (1) position. With the key in run (2) position, the left signal blinks fast in either left turn or center (no turn) and fast on the right side in right turn. It seems to me that low voltage makes a fast blink, other than a bad lamp. Any ideas greatly appreciated.

Update: I have also just learned that the hazard signal blinks at the normal rate and supersedes the turn signal. Also, if I turn the key slowly from off to 1 and stop turning just as the accessory power kicks in, but before the click into position 1, the turn signal blinks at the normal rate in all three positions. Thanks

I'm generally a simple things first type of guy. Have you looked at the lamps to see if someone put an LED lamp in the mix somewhere? (Not sure how long you have owned the car) The different draw could do something.

From your description the problem would seem to lie with the ignition switch. In certain key positions the ignition switch is altering the normal resistance value of one or more light circuits. The flasher unit is reading this altered resistance as a false indication of a "lamp out" condition and is responding by raising the flashing rate to its alert status.

I can't imagine anything in the wiring or turn switch which would cause this. Normal behavior when not enough current is drawn by the bulbs. Usually due to a bulb filament being out, but can also result from using LED bulbs (draw much less current), as mentioned.

Cheap, basic flashers do this. I don't think it is intentional in the design, but can be thought of as a useful diagnostic. You can buy electronic flashers that have a constant flash rate, insensitive to current draw. Some will even play Elvis', "Love Me Tender" as you signal (quickly proved bothersome to me). You can also buy LED bulbs with a resistor to draw more current. Wasteful, but one way to keep using a cheap flasher w/ LED's.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans

Original post is from June, has the problem been fixed yet?

If the turn signal bulbs are not from different manufacturers, then maybe there is one or more faulty ground path?

I thought I had a failed right front turn signal harness on my 78 W116 300SD that turned out to be a poor ground connection.
W116 right front turn signal electrical gremlin

Follow the negative wires (usually brown) from each turn signal socket to where they ground to the chassis.

Disconnect the negative cable from the battery.

Re-establish a good ground by removing the grounding screw, exposing bare metal at the chassis and cleaning
all the ground wires at the connection with electrical contact cleaner before you reconnect them back to the chassis.

Reconnect the negative cable and hopefully enjoy properly working turn signals.

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78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022