Adding A "Sport" Mode To Your Transmission by way of Kickdown Circuitry
Let me first address the concerns that a few people have voiced about this type of modification. It has been suggested (not by me) that wiring in a kickdown switch override or auxiliary kickdown switch will wear out and/or destroy one's transmission.
I don't think this is true, and here is why. Sure, if you just spliced the wires leading to the switch together so the car is always in kickdown mode, you would probably prematurely wear out the transmission. Fair enough. However, I believe that having a switch wired in properly that activates kickdown mode under less than full throttle is relatively harmless, for two reasons.
First, kickdown is a misleading term in the case of these transmissions; what actually happens is that the transmission's shift logic is altered, allowing downshifts under less (seemingly about 50% less) throttle and holding lower gears longer. Thus, having this operation take place under half throttle would seem to be less stressful than the same action taken under WOT. The kickdown solenoid may wear out faster, but it is relatively cheap and very simple to replace. How could half-throttle downshifts be worse for the car than full-throttle downshifts? Besides, the car downshifts without the kickdown anyway.
Second, I performed this modification 50,000 miles ago, and have experienced absolutely ZERO problems. I have changed my transmission fluid and filter twice in this time, and there has been no bizarre shrapnel in either. So, my own experience suggests that this is a perfectly safe thing to do. I have also heard from people around the world who have done the same with similar results. That said, this is a non-factory modification, so perform at your own risk, blah blah blah.
So, let's get started. First, it is very important to wire this switch in the manner shown in the diagram I provided. Crossing the wires will leave the car in KD mode all the time, and wiring the OEM switch out of the equation will prevent kickdown from occurring under typical kickdown conditions (with the switch off.) Splice one wire into each of the wires coming out of the kickdown switch (located under the gas pedal.) Then run these wires to any simple two-pole switch of your choosing. This switch needs to be a toggle-type switch, not a momentary switch. The circuit must remain closed while the switch is in the on position.
I personally prefer to make any modifications look like expensive, rare factory options, so I decided to go with a factory MB two-pole switch. The only switch that fit the bill was a rear dome light switch, so I ordered one on Feebay for five bucks. Installing it was simple; I removed my rear antenna switch since my aftermarket stereo controls the antenna anyway. The antenna switch needs to be connected to its' plug to keep the antenna functional with the stereo wired as I have it, so I simply cut the octopus leads on the switch and plugged it back in behind the climate control panel, out of sight and out of mind. Sure, I could have spliced the correct wires together instead of just putting the switch back in behind the panel, but this works just fine. You can take the switch out without removing the panel, but the panel needs to come out anyway to run wires to the kickdown switch.
From there, I decided that I needed a decal or emblem of sorts to indicate that the switch triggers "sport" mode and is not simply an upside-down dome light switch. In the interest of combining a sort of "MB inside joke" and making the car look to the untrained eye like it has an expensive factory option, I selected an original-style AMG logo. The size of the Affalterbach emblem on a set of valve stem caps I found on Feebay seemed right, so I bought a set. The logo looks pretty cool on the switch - the photo shows the switch in "AMG" mode.
As for the 50,000 miles I have logged with this switch, I tend to only use the switch when needed rather than leave it on all the time. Downshifts occur when the economy gauge nears the middle of its' travel - I suspect that "AMG mode" may also help fuel economy a bit! It is a great addition to my 300SE, letting the M103 take full advantage of its' power band. I use the switch for rapidly merging onto freeways, passing on rural highways, or just generally smoking lesser vehicles like so much Nova lox. It is also fun to convince passengers that your car has the super-rare "AMG transmission" that only you have to know did not exist!
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"It has been my experience that folks who have no vices have very few virtues." - Abraham Lincoln
DIYMBREPAIR.com is a credit repair site, has nothing to do with MB. It's referenced on this forum in several places - either it's out of date, it's been hijacked, or something.
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