W126 keyless entry installation
 

I just installed a keyless entry system in my 89 420SEL. I used the system shown over on the W126 coupes web site.

http://www.mbcoupes.com/audioalarm/alarm/keylessentry1.htm

Great price & it works as it should. Only one minor difference in my 89 SEL's wiring harness for the pneumatic lock modual compared to the 85 SEC's.....the red/black wire described on the
SEC is red/white on my SEL. No biggie, just thought I'd share.

Thanks Jim Ham for supplying this info for all to see!
Now I don't have to worry about scratching my doors with the keys anymore. :D

did it affect your factory alarm system in anyway? The reason I ask is on my 1988 560sel if you lock the driver's door with the key and try to unlock the passenger door with the key - the alarm goes off. I then have to lock the passenger door and run around and unlock the driver's door with the key to disable the alarm. I was just curious if releasing the locks from the trunk will trigger the alarm or if you lock the doors with the keyless remote will the alarm even be activated? I have heard that there is a mechanical mechanism in the driver's door that is used by the key to arm the alarm. Is your alarm disabled when you lock doors with keyless unit? Thanks. If everything is good, I will definately install one in my car.:confused: :confused:

An alternative solution
 

Neat idea.

For those looking for a more comprehensive solution, consider the Code Alarm available from Crutchfield:

http://www.crutchfield.com/cgi-bin/S-zfzIxvRCv7P/ProdView.asp?s=0&c=2&g=802&I=514REC11&o=m&a=0

I paid about $100 with the necessary relays and diodes (Radio Shack) and have the whole thing wired into the vacuum pump in the trunk of my 1990 560SEL. The advantage is that this installation optionally allows visual confirmation (1 flash of the parking lights=locked, 2=unlocked) and aural confirmation (I used an old horn from my BMW bike mounted outside under the rear deck, and a relay - the Code Alarm beeper is way too quiet to be heard).

This should take a couple of hours but took me much longer as Crutchfield provided the wrong relay holder/wiring. However, they did work with me to sort it out.

On a good day mine has a range of 60 yards.

You can also set it to lock the doors when you start the engine, but in my case that also sets off the factory alarm and I have not yet worked out how to defeat that 'feature'.

I have had it in daily use for 9 months now and the only thing that has gone wrong is the battery died necessitating reporgramming, a DIY job. The kit comes with 2 remotes.

If you want to use this on earlier (pre-1986 I would guess) cars that do not have the auxiliary vaccum pump, you will have to deal with the additional complication of lock actuators.

I havent had any problems with the alarm since the installation. I honestly couldnt say if the alarm is activated or not. It should be according to the instruction on the MB coupes site. I'll see if I cant get the alarm to go off while the doors are locked in the next day or so.

Thanks Clay
I appreciate it.
Maurice

Moedip,

If the alarm goes off when you unlock the passenger door, see if it goes off if you twist the key to the lock position with the door open. It might save you 20 or so steps.

Sixto
91 300SE
87 300SDL
81 300SD

I'd validate that the actuator has to use the trunk wire. On a W124, using either door wire doesn't set or upset the alarm. The W124 alarm wiring looks just like the 91 W126 alarm wiring.

I'm not arguing with empirical evidence, though.

Sixto
91 300SE
87 300SDL
81 300SD

Re: An alternative solution
 

Don't all W126 sedans have a vacuum pump? My 81 SD has a vacuum pump in the trunk just like my 91 SE. Maybe only the pre-86 Diesels have a vacuum pump.

Sixto
91 300SE
87 300SDL
81 300SD

Re: Re: An alternative solution
 

Yes. I believe mine is underneath the rear seat.

Re: Re: Re: An alternative solution
 

In the SDL? Isn't there a blob of foam with wires and vacuum hoses leading to it in the right rear corner of the spare tire bay?

Sixto
91 300SE
87 300SDL
81 300SD

That's what I've been told by others - never had to need to investigate myself.

Hmmmmmm
 

Moedip....I haven’t been able to get my alarm to go off at all.

According to the owner’s manual, the alarm will go off if the brake pedal is depressed with the doors locked and the ignition off.
So I locked the doors with the driver’s window down and depressed the brake pedal with a broom stick...no alarm.
I popped the hood with the doors locked...no alarm
I locked the driver’s door with the key and then unlocked the passenger side with the key...no alarm. I locked the passenger side with the key with the door open...no alarm.

I tried all of the above with the key & keyless entry.

I can’t think of any other way to get the alarm to go off.
Does anyone know of tried & true way to do it? Or should one of the above procedures made it go off? Perhaps my alarm has been disabled with the keyless enrty.:confused:

Hi Clay - that is what I was worried about. I have read sevral times of problems installing aftermarket remote car starters, alarms and door locks on Mercedes. The install you did sounds so easy I am tempted to try it. Maybe we can get lucky and either Dave Petryk or Mike Tangas will join the discussion and give us some help to keep the factory alarm so it works with the remote. (hint hint):p :p :p
Maurice

Code Alarm and the MB factory alarm
 

FWIW, the Code Alarm preserves the working of the factory car alarm. (See my post above for the one exception - I have disbaled the 'lock doors on start' to avoid having the MB alarm go off - otherwise, the MB alarm functions as designed).

The Code Alarm has a lot of programmable options, as well as a panic button mode. It also offers a starter disable option (you need another - heavy duty - relay for this) but that s/b redundant with the MB alarm remaining fully functional.

One final generic thought on remotes - true for my Code Alarm and the wife's factory remote for the 1999 E320 - hold it under your chin pointed upwards when you press the button and the range is vastly increased (at least 2x) - must be something to do with the skull acting as a parabolic reflector. Of course, you also fry your brains in the process....

420,

Check the alarm controller in the passenger footwell. Lift the mat and carpeting and remove the board. There should be an approx. 6" x 10" box with 2 long connectors with about 12 pins each. When the door switches get flaky, a common fix is to disable the alarm by disconnecting the controller.

Sixto
91 300SE
87 300SDL
81 300SD

I am considering installing the top of the line Crimestopper Informer alarm on my 420. It has all sorts of bells and whistles on it including keyless entry and remote start. It has its own siren too. Could I install this w/ no problem? Couldn't I just disconnect the factory alarm and start with a clean sheet so to speak?
www.crimestopper.com

You can disable the factory alarm by disconnecting the two plugs. That should leave you with a fairly clean sheet. In fact, most of the connections you need will be collected in the alarm box area. You can even use the factory alarm horn instead of that annoying multi tone siren that no one pays attention to anyway.

Sixto
91 300SE
87 300SDL
81 300SD

Isn't the alarm box area in the passenger side footwell somewhere?

"Check the alarm controller in the passenger footwell. Lift the mat and carpeting and remove the board. There should be an approx. 6" x 10" box with 2 long connectors with about 12 pins each."

That's what the guy said. Wait, it was me :)

Sixto
91 300SE
87 300SDL
81 300SD

420,

did you have to perform that surgery on the circuit board? i wanted to try this but that part sort of intimidated me. i'm also wondering if anyone has ever attempted this on a W124. there is an alternative method using Crutchfield components but it seems somewhat more complicated. i'm almost sure the connections are available in the w124 trunk because you can lock / arm from there...

jsmith wrote.

"did you have to perform that surgery on the circuit board?"

Yep. I wasn't too difficult to do but I do have some soldering experience from working on RC cars in the past. It can be frustrating so I'd get some practice in before you try this.

What do you guys mean by surgery and soldering? Those to wires and connectors don't just pop off to disable the factory alarm?

mbtjc,

we are dicussing the adaptation of the JCWhitney Valiant system for W126 & possibly a W124. if you read the step by step procedure in that link ath beginning of the thread, you'll see that you have to open up the Vaiant unit and do some minor soldering / modification to the printed circuit board.

lock doors after engine start
 

this sounds like a nice to have feature but it really just gave me a lot of aggravation in the family van. i would start up the engine, which would then cause the doors to lock. whoever was outside would then try to open the door while i was trying to unlock the door which of course is mutually exclusive. repeat a couple of times and it gets really annoying. this went on until one day i got really tired of it and disabled that feature...

could you rig this up on a pre-86 model with an electric pump? i have an 83 300SD that i would love to rig up keyless to, dont care about the alarm. Car doesn't have a factory alarm. If i could install myself for 40 bucks i'd do it over the summer!!! thanks
Ryan

Ryan,

The procedure described at the begining of the thread will work on any US W126. You don't have to worry about the factory alarm since your 83 doesn't have a factory alarm.

Sixto
91 300SE
87 300SDL
81 300SD (on ebay)

sixto,
you know if this has been done on a w124 successfully? the crutchfield solution is tried and tested and even at double the price of the jcwhitney solution it is still a good deal...

I don't know if anyone's done this on a W124. I can't imagine it would be any different. the only real difference between the W124 and W126 is that the W124 pump is under the rear seat.

I prefer the Crutchfield solution myself since I can't solder to save my life and the benefit of Crutchfield support seems to be a worth the extra money.

Sixto
91 300SE
87 300SDL
81 300SD (on ebay)

Crutchfield support on Code Alarm
 

I should add that I did not find Crutchfield's support to be that good - it required many calls before they figured out they had sent me the wrong relay connector. The way 'they' figured it out is when they sent me the wiring schematic and I realized I had the wrong connector. I did get a full refund on the part, though.

This does trsanlate into a waste of time and distrust of the vendor.

Eventually, I made my own relay connector by following the schematic and bench testing the whole thing with a 12v supply. All that bending over into the trunk/pump area gets really tedious....

I bought the third relay and socket for the horn and the diodes for the flashing lights (you only have to connect the rear ones to get all four flashing) at a local electronics shop. Very inexpensive.

ok, i pieced together all the information and realized that all that was really involved to do the keyless part of it was to send power into the unit and the to figure out which wire would do the lock / unlock. apparently on the w124 it's that blue wire that's connected to the vacuum pump. i could brobably go in the trunk but i hate having to do trial and error since nobody seems to know about the connections back there for the w124. i picked up a jcwhtney keyless entry that says it has built in relays and works with vacuum pump systems. i will be sure to post my results...

I installed JCwhitney Valiant remote controller on my W124( 92 400E) 2 months ago, it's running perfectly, I got the idea from mbcoupe.com:

http://www.mbcoupes.com/audioalarm/alarm/keylessentry1.htm

But I got the cheaper version of Valiant, it has only 2 buttons(lock and unlock), the original valiant system described in mbcoupe.com had 3 buttons, the 3rd button was wasted(for trunk release).

Because my 2 button Valiant has different PCB layout, I did figure out the proper connection by a multimeter and cut some tracks on the PCB, also soldered some wires on the PCB, then I also mounted the receiver on the back of tail light.

By using exact the same remote controller as described in mbcoupe.com, you just need to completely follow the instruction. For W126 and W124, the color code for the wires may be different, the control line is yellow, the +12V may be Red or Red/White, the Ground may be Black or Brown. It's good to verify it with a multimeter first.

carman850,

i think that's the same one i have - haven't gotten it yet. can you explain the need to rewire the unit? i thought i had it figured out from:

this explanation

it appears that all you need is for it to send a + or - 12v to the vacuum pump and it says there are built i relays. i had decided that wiring at the pump itself was more straightforward...

Joe,

Mercedes uses unusual center door lock, there is only one wire in each front door and trunk which controls the center door lock, when this wire has 0 voltage (Grounded), it unlocks all doors, when it has 12V voltage, it locks all doors. when it doesn't operate, it stays with high impedance. Please note, it doesn't require a constant voltage, all it needs is a longer than 2 second pulse to allow center air pump under the rear seat to finish the operation.

So the object of the add on remote control, is to ground that wire for about 2 seconds when "unlock" key is pressed, and to connect the wire to 12V voltage for 2 seconds when "lock" key is pressed. After that it should maintain the original connection, one may still be able to use key to open all door.

If you ordered the 3 button Valiant remote control, it has 3 relays, one closes for about 2 seconds when "unlock" button is pressed, and one closes for about 2 seonds when "lock" button is pressed, the 3rd one is for remote trunk release which you don't need. You can not just simply use one relay to ground it, and use the other one to connect it to +12V, because if you accidentally press one button right after you press the other one, you will have a short circuit.

Because Mercedes is unique, you need to modify the PCB board for the target above. I have attached the schematic from mbcoupe.com, the author was very smart to put two relays in serial, it doesn't interfere the existing mechanism at all, and there is no risk of short circuit.

It'll also be good if you install it near the air pump, only the control range may be less due the shielding caused by metal body and tint glass.

thanks, that finally makes sense. i think i only ordered the two button remote. i guess i'll have to take a hard look at that pcb and see if i can figure out how to do the same modifications.

and yes, the main reason i would put it in the trunk is to get the extra range...

carman850,

from the schematic and from checking the relay functions, i determined that the momentary contact poles are shown in this picture. i figured that the connection between those two are what need to be snipped. it appears that the etchings are on the other side of the board. now did you have to desolder and remove the relay to get at the connection between the two pins?
help! i didn't count on having to do that - i just might send the thing back!

thanks

Joe,

It's too bad, the track connects those two pads is on the component side of the PCB, it's under the big black relays, you have to use desoldering gun or vacuum gun with a solder station to remove the relays in order to access that track.

Rats! Anyway, thanks for the confirmation - I might still give it a go. If they had only not connected those two, this little unit could really be a Universal keyless remote. I figure you only need to solder one of those pins to ground and then use the other connectors.

My two button Valiant has only one remote, it doesn't look as nice as those OEM ones, more like a cheap toy for kids.

two button version works good!
 

it's not really that cheap looking :( , my $300 Viper remote start in the family van only has a few extra buttons but otherwise does not look that much better. all in all this is an excellent value at $40 shipped.

for those interested in doing this - i did have to desolder one of the relays and snip the connection between the two contacts i mentioned previously. not a big deal, you can get a $3 desoldering bulb at RS. then i had to jumper the lock relay contact to +12v. the other contact still had a wire that i simply spliced into the black (ground) connection. the rest i accomplished by splicing the wires together (relay series connection). i stuck the finished unit in the cranny above the right tail light with velcro and snaked the wires down underneath where i spliced into the trunk lock actuator harness. it passes directly underneath which is very convenient. the harness is sheathed in black and you have to cut through to get to the yellow, red and brown wires. i drilled a hole in the tail light assembly and stuck the antenna thru there and secured it with a small piece of duct tape. the range is pretty decent and it works as advertised including arming the factory alarm.

if you're not interested in features like flashing confirmation lights & beep etc, this is the easiest way to go. if you need other features you will have to wire into the convenience module underneath the rear seat.