Bypass Ignition Switch

[Charlie Buckett]

I replaced my Neutral safety Switch - no joy - it must be the ignition? and so I have been starting the car by jumping from the + battery terminal across to the three prong plug. But would like to connect a switch to keep me from being under the bonnet everytime I need to start the car.
I am bad at electronics, I am simply thinking to run a thick gauge wire, connected by a clip, from the solenoid and another from the + battery terminal into the cabin and connect them to a switch. Sounds to simple, is there a particular solenoid point I need to connect to? Will I fry the ecu at some point (been doing this for few months now and no harm yet)?
Any other recommendations, wire gauge/type of switch/relay in circuit (whatever that means)...?
I was quoted $700 for new ignition.

[AMG]

1. Is the neutral safety switch correctly adjusted and do you have new bushes installed on the transmission selector rod? check this first.

For ignition switch price - Ring the forum sponsor. Tell them I told you to ring them.
a new ignition switch is not expensive. a new ignition key barrel (which you replace if your key starts to get stuck while turning) is not expensive either. Including the time it takes for a professional auto sparky to fit both, it would amount to less than $700 all up.

Don't think for a minute that you can jump your car through a pushbutton switch. the inrush current to the starter switch will set fire to it in no time flat. You do realize we are talking in the vicinity of 4-600 amperes when you bypass the solenoid.

The ignition switch is set like this for a reason. You don't need to be einstein to work out how to do fix it either - it's as easy as the neutral safety switch on the side of the transmission.

2. no it is not good for the vehicles electronics - it is a matter of time before you kill the OVP relay, then the fuel pump relay/MAS, then the ECU.

if you still think it's too expensive go to a wrecker and get the ignition switch off the column. Chances are it's just as stuffed as the one you have in the car.

The reference library section has information on the w124 electrical troubleshooting Manual - aka ETM. It's worthwhile looking there for valuable learning information.

It's also worth talking to members of the Vic MB club - they have a good wealth of technically minded members.

[Charlie Buckett]

Thank you for your reply/advice.

The NSS is correctly adjusted, I used the guide hole with an allen key to be sure, reverse lights come on (oddly they come on even when I delibertely misalign). I also replaced the bushes not long ago. Headlights dont dim at all when I turn the key.

And because I can start the car by jumping from the + terminal across to the middle prong of the 3 prong plug opposite the battery (Is this dangerous?) I presume the solenoid is working, but that only leaves the ignition switch. The tumbler is fine, key and tumbler move smoothly.

[MMWA]

you don't have some silly aftermarket immobiliser installed in there do you ?

[AMG]

you don't have some silly aftermarket immobiliser installed in there do you ?

Good point. I'm so used to the mandatory immobilizer-removal practice that I completely forgot to ask.

There is a fusible link also, but that's unlikely to be the culprit, as everything works, except for the ignition switch, so it's just a case of check/replace fuses, clean all contacts and modules, OVP etc.

[AMG]

Thank you for your reply/advice.

The NSS is correctly adjusted, I used the guide hole with an allen key to be sure, reverse lights come on (oddly they come on even when I delibertely misalign). I also replaced the bushes not long ago. Headlights dont dim at all when I turn the key.

And because I can start the car by jumping from the + terminal across to the middle prong of the 3 prong plug opposite the battery (Is this dangerous?) I presume the solenoid is working, but that only leaves the ignition switch. The tumbler is fine, key and tumbler move smoothly.

The switch is not difficult to replace, but you do need to be a bit of a contortionist to get in there to see it - easier and quicker to push seat all the way back - sometimes easier to remove it (if it's a manual seat, I'd remove it) to allow you to see under the dash.
it's a one-screw affair, but getting the big rubber cover off the rear can be a bit of a pain - I spray some inox on the back and it slides a little easier.

then the connector simply pulls off the switch.

This makes it a good time to check the wiring for any scorch marks, which is an indicator of a more sinister problem - high resistance somewhere in that particular circuit, which means getting out the multimeter and measuring resistance down the wire until you cover off each of the component feeds that hang off that particular feed. - it's not a complicated task, it's just time consuming when you have to check the ETM schematic for each colour, then check the component locations to find the connectors and pin number on that connector which you need to probe.

Despite the preceived complexity, the logical method of the schematic and the component location PDF's make it easier to test. If this was a different car - say a 1992 Range Rover Classic (I'll just use it as an example) then the horrific pommie schematics combined with the horribly invisible and infinitely variable / missing locations combined with the Price of Darkness' oversight, means you have no hope in hell of being able to determine where the smoke escaped from.

Thank your lucky stars you own a Mercedes - because at least there is an instruction manual which tells you what the wire colour is, where it goes and where you can find the connector. :occasion5:

[Charlie Buckett]

Thanks guys.

No Immobiliser.

I just remembered I had an old complete steering collumn in the shed.
I am supposing that this is the switch that needs replacing? (I cant see any screws or such that remove it, just 3 rivets).
I have googled all morning and every search just brings up the ignition tumbler assembly removal. I think I just need to replace the switch. Does anyone know a thread or link that addresses this? The NSS was very easy but this looks much more difficult. And my back is dodgy.

I think I may just have to keep jumping from the positive battery terminal to the three prong plug opposite the battery until I kill either myself or the car. (has anyone else started there car this way?)

[Charlie Buckett]

you don't have some silly aftermarket immobiliser installed in there do you ?

Well I never thought I did, I have never needed to press a button or any other such thing, but what is this speaker doing under the ignition?
The car did have a car phone/microphone from the 90's installed, could it simply be that, or is it part of an alarm (the sticker says to aim the speaker at the driver, then to remove the sticker). The speaker wires lead toward the stereo, I can't see any other aftermarket component though (suppose I'll have to remove centre console bits to follow speakers wires.I have decided to try and do this properly, but didnt realise I need to drop the steering wheel for enough clearence to remove the ignition, another first for me.

[Tony From West Oz]

The speaker does look like those which were installed with earlier car kits for mobile phones (Nokia et al)
You may find the car kit electronics box in there. It may also have a connection to the car radio to mute it during a call.