1994 E500 won't start - due to alarm or radio?

[bpat]

Hi guys. My '94 E500 green machine has been my daily driver for years. I have an aftermarket but plug-and-play Continental TR7412UB-OR stereo which I love and which has been working fine. I recently replaced my front under-dash speakers because they intermittently didn't work -- actually I had them replaced. I don't have the time or aptitude to do much of this stuff myself.

Anyway, about a month ago I noticed that the dome light did not go out when I started the car as per usual. Then later the same day the stereo started acting weird; the face lit up but no sound and the antenna did not raise. Then the car intermittently wouldn't start . Turn the key and nothing would happen under the hood, although the electrical accessories would power up. I drove it to my local dealer (Medford, Oregon) where it wouldn't start at all.
They found that the rear window actuator didn't work and needed to be replaced. I knew about that but of course but it didn't address the problem I came in for. They can always find a way to spend my money. I let them do it. But it took them over a month to figure out the no-start problem. Apparently the car is older than their manuals and most of the people who work there. Eventually they decided that the problem was related to the alarm system (which hasn't worked since I bought the car over 10 years ago; or at least I've never had the fob for it) which they said is locking out the start up. They say they figured this out by bypassing the alarm after which the car would start. They suspect that my radio is at fault because the alarm system is somehow channeled through or otherwise connected to the radio. Who knew? I brought them the original head unit (I have 2 of these) to install but they can't get my current one out because they say that the removal keys I brought them don't fit. I can't swear they're wrong about this; maybe I gave them the keys to the original unit. But for now I can't find any others.

Does any of this make sense? Is it time for a new car? Mine was running great until it wasn't running at all. By the way they say that a local audio shop couldn't remove my head unit either because they don't deal with Continental, so I know at least they're trying.

Any ideas or suggestions?
Bruce

 

[gsxr]

1993-up 124 chassis have a starter disable built into the alarm system, so in theory that is possible. And it can be easily bypassed if desired.

However, normally the radio has NO connection to this system. Unless someone did really weird stuff when installing the radio, that should have no effect on starting.

BTW, I assume when you say "no start", you mean you turn the key and nothing happens, the starter does not engage, there is no click, nothing.

 

[bpat]

That's exact;y right, turn the key and nothing happens. Thanks for your reply. It didn't make sense to me that this would have anything to do with the radio. The new radio is just plug and play with no wiring required. Someone did install new speakers.

 

[nocfn]

On my dad's 94 E420 (from PNW) The alarm system was disable, but behind the cluster was some type of alarm after market wiring.

Is there an alarm module in the PS FLOOR lime a w126?

 

[Jlaa]

brought them the original head unit (I have 2 of these) to install but they can't get my current one out because they say that the removal keys I brought them don't fit. I can't swear they're wrong about this; maybe I gave them the keys to the original unit. But for now I can't find any others.



Any ideas or suggestions?
Bruce

IIRC with the 92/93, you have to undo the ashtray area wood in order to take out the head unit as well — Is that the same on the 94? Is the dealer undoing the ashtray area wood when trying to remove the Continental?

 

[TerryA]

Is the alarm system stock or an aftermarket unit?

FYI, My 84 500SL had a Derringer Alarm wired in.
In this system if the battery is disconnected the car will NOT start when it’s reconnected. After reading the alarm manual I discovered a button inside the glove compartment that had to be engaged (pushed in) while starting (turning the key to start) the car.

The Derringer system was designed to foil a thief that disconnect the battery to shut off the noisy alarm. When the battery is reconnected car won’t start unless you know where the secret button is pushed.

Anyway, stock or aftermarket alarm check the manuals.

Just my $0.02

 

[gerryvz]

Check your fuses first !! That's ALWAYS your first step. The fuses, specifically to check, are fuses "5," "B" and "C" in the fuse box on the driver's side underhood. But, CHECK/REMOVE/ROTATE ALL of your fuses !!

Quite often, the alarm boxes fail on these cars with time and age. When they do, they must be unplugged/disconnected.

The facelift W124 cars have a relay, which is located behind the instrument cluster, which controls the starter lockout. This is called the K38 relay. There is a thread about it here:

K38 Relay | Electrical, CAN and Wiring

Has anyone had the K38 relay behind the instrument cluster fail and prevent the starter from engaging on an intermittent basis? I can't seem to find much information on this forum about the K38 relay. I am trying to help a guy over on peachparts troubleshoot his 400E. He said the starter is...

www.500eboard.co

In particular, this post should help you: K38 Relay

If you jumper two of the pins (I think pins 30 and 87....NOT 87A) on this relay, it will eliminate the immobilizer that is also controlled by the alarm system. IIf you do this, you also MUST unplug the alarm box under the front passenger side footwell.

Cheers,
Gerry

 

[bpat]

Well the dealer has decided to punt. Basically they say that they don't know what's wrong and they can't fix it. They got it to start by bypassing the alarm but the radio still won't work (it lights up but there's no sound; tried 3 separate head units) and the fasten seat belt light stays lit no matter what. They agree that there's an odd electrical gremlin but they can't identify it.

They say that as a long shot they could replace the all activity module (AAM) if they can get one from Germany but they have no confidence that will fix it. They imagine that I could get the stereo to work by having an audio shop rewire everything to bypass the Mercedes amps and directly power the speakers from the head unit. I don't love that idea.

It feels like a permanent workaround for an underlying problem we're not fixing. These problems all started on the same day and I assume have a common cause that they just can't identify. I'll try the fuses when I get it back form the dealer. They've had it over 2 months now.

Anyone know any particularly clever independent mechanics near southern Oregon? I may be looking for a new vehicle. I can keep driving my old 560SL in the meantime.

 

[gsxr]

I'm not confident the dealer knows what they are talking about. I've never heard of an "AAM" on the 124 chassis, or anything that might be confused with an "AAM". The stereo system should be 100% isolated from the engine starting system.

As a wild shot in the dark I'd inspect/replace the ignition switch, located behind the ignition tumbler. Has this been investigated yet?

 

[bpat]

Yeah, the dealer admits that they're stumped. And from what I can figure out the AAM may have been associated with the ML320 series of the time, not the 124. And the radio is clearly not to blame, though it's affected by the same gremlin. The ignition switch hasn't been checked that I know of. That might be beyond my capability. Thanks for the suggestions.

 

[gsxr]

My keyboard diagnosis is either an ignition switch failing (replace and see what happens), or a loose ground connection somewhere (far more time consuming to trace).

This assumes the basics have been covered, starting with making sure the battery terminals are tight, specifically BOTH nuts on the positive terminal.

 

[nocfn]

(not to highjack but it may help a future search) If you buy ignition switch and or headlamp switch, buy MB and not after market. The two switches that control the most current on the car are those two, and they have lasted 25 years. Pay the slight premium and get genuine MB switches.

 

[bpat]

Thanks. How hard is it to change the ignition switch? Is it something that I could probably do with commonly available tools? I assume I could order the part from the dealer.

 

[gsxr]

Thanks. How hard is it to change the ignition switch? Is it something that I could probably do with commonly available tools? I assume I could order the part from the dealer.

The easy part is buying a new OE/dealer switch. Installing it is a PITA... I've not done it on a 500E, but I did do it on my old 87 300D and it wasn't fun. There's limited space to fit your hands and/or tools, and you can't see some of what you are working on without a mirror.

IIRC you remove the lower trim cover (knee bolster) and work from below, but pulling the instrument cluster may help also. Might be a "How-To" somewhere on this?

 

[bpat]

UPDATE: I took it to my indie mechanic where most everything seemed to be working aside from the stereo. The Mercedes amps were no longer working, so they just bypassed them; the speakers are now directly powered by my Continental head unit and it sounds fine.