W126 alarm wiring

[944S2cab]

I need to fit a new alarm and immobiliser to my 1991 W126 300SE.

My copy of WIS does not have wiring diagrams. Does anyone know where I can get a wiring diagram showing the functions of the existing wiring?

Thank you.

 

[grober]

Don't think the w126 of that age had a factory fit alarm [ USA models may be an exception?] so any alarm wiring you have at present will be after market or dealer fit and undocumented. They all follow basically the same pattern with input tied to the door switches and ignition and possibly ultrasonics if fitted. Immobilisers normally break into the fuel pump relay/OVP relay/ starter motor solenoid circuits by placing a relay in series with their signal lines. Most alarms come with instructions how to fit them or just get it fitted by an alarm specialist?

 

[Dec]

May be of some help, the diagrams below are for a Scorpion alarm around 1993.
What remote fob, if any, do you have?
Any odd looking keys with that car?

Dec

 

[944S2cab]

Thank you grober and Dec.

I only received 2 keys with the car; one for door locks and one for ignition.

The fob is like the one in Dec's diagram. When I got the car the alarm module (part no. Q3 50 06918) was loose in the glove box. Not a good sign. Someone with more knowledge than me must have thought it was faulty. I've opened it up and cleaned the printed circuit board with electrical cleaner. I reconnected it but nothing happened.

The fob shows a red light when the buttons are depressed so I assume it is OK.

The wiring diagram is helpful. I'll have a look at the car's wiring tomorrow and see if the colours correspond.

 

[Dec]

That part number is for a Scorpion 918 and the diagrams are for a 918.

Check if there is a Red LED on the dash, it should illuminate (and blink, I think?) when the car is locked with the two button remote to indicate that the alarm is armed.

Any sign of the alarm siren in the engine bay?

You could give Scorpion Alarms a ring to see if the can offer any advice… Scorpion Automotive - Supplier and manufacturer of vehicle security alarm systems and mobile communication Interfaces - Contact Us … have the part number to hand if you call them.

Dec

 

[grober]

I think Q3 50 06 918 refers to a Scorpion 918 alarm. which is probably the one DEC has posted. Your car should also have a [ red or black]siren unit [ containing backup batteries] under the bonnet somewhere but may have been removed if its gone faulty. I would seriously consider just getting an entire new setup fitted- new control unit/wiring/switches/siren [ basic setup will do --ultrasonics are notorious for false triggers for example and more trouble than they are worth ] Because such an old alarm system has the capacity to totally immobise the car should it go faulty the unreliability inherent in an old system [25years plus] should not be ignored. These devices are OK to repair/ fiddle with in your garage with the right tools and visibility but not at 11pm on a wet night on the hard shoulder of a motorway----- don't ask!

DEC beat me to it again

 

[Dec]

I'm just too fast for you. I agree, it's probably just better left alone, it was disabled by the previous owner for some reason, it could have been causing starting (immobiliser) problems or draining the battery.

Dec

 

[944S2cab]

I was intending to buy a new system and fit it myself. I was hoping to identify the functions of the existing wires and connect the appropriate new wires to them. However, if there is a problem with the existing wiring I may not have the knowledge to sort it out.

On balance I think I will get a professional to fit a new system. Can anyone recommend a fitter in north west England, please?

 

[grober]

Because most modern cars come with built immobilisers and alarms now the number of alarm fitting companies has diminished. Much more likely to be combined as IN CAR ENTERTAINMENT AND SECURITY OUTLETS.
This would be typical in Cheshire?
Approved Thatcham Car Alarm Installations - Sounds Alarming Welling

http://www.soundsalarminguk.com/contact.htm
I know nothing about them personally but they are Thatcham approved[ if still current?] so I guess must meet certain standards. If you are lucky they may remove your old alarm FOC. Otherwise try your local yellow pages