An index of useful guides designed to help you care for and maintain your Mk3 Cavalier
#160084 by Robsey
Sun Nov 06, 2016 11:09 pm
System 90 Alarm System – Type 901


This model of alarm is used on early vehicles from 1982 onwards including, Nova (Corsa A), Astra 2 (Kadet E), Carlton (Omega A), Cavalier 2 & 3 (Ascona C & Vectra A), Midi, Brava and Rascal.

For the most part, I am reproducing the details in the fitting instruction manual “TD 4733”, except that I will put my own slant on this, as I feel that these instructions are not what I would see as being wholly adequate. This mainly refers to the wiring up section.
No apologies for being pedantic about doing the job to a proper standard - if a job is worth doing, it is worth doing properly – especially if it is your pride and joy.
There are others who get by with bodges etc., such as twisting wires together or using Cellotape. I have seen it done – even by so called professionals.
I have also edited out fitting and wiring instructions for the other vehicles as it is a Cavalier Forum after all.

Okay let’s see what the manual says.

901 – System 90 Alarm Unit – part number 91143121 - replaced with part number 91145765.
902 - System 90 Alarm Unit with Integral Remote Control wiring - part number 91143122
903 – Remote Control for System 90 alarm unit – part number 91143123
904 – Ultrasonic Sensor – part number 91143124
905 – Microwave Sensor (Not Cavalier Mk3) – part number 91143125
906 – Starter Inhibitor – part number 91143126
907 – Battery Back-up – part number 91143127
908 – Central Door Locking Motor – part number 91143128
910 - Fuel Pump Inhibitor - part number 91145819.

Window Stickers – part number 91143189
System 90 Pin switches (2 pack) – part number 91143190
Rear Door Pin Switches – part number 90213038
Boot Pin switch – part number 90347641
Hatch Pin switch – part number 90355384
#160085 by Robsey
Sun Nov 06, 2016 11:10 pm

Arm / Disarm – Activation “Beep” Jumper – Remove Jumper to silence activation Beep
(Jumper is located behind socket P1)

P1 – Volumetric Sensor input.
For Ultrasonic Sensor – 904
(For use to detect glass breakage and entry into vehicles other than via the doors)
For Microwave Sensor – 905
(Used to protect the interior in Convertibles).

P2 – Status Monitor Connector
(Switching between on, auto and off should be done with the ignition ON)
Status Monitor part number - 91145767
Mini loom for status monitor - 91145775

P3 – Optional Remote Control Connector – 903

P4 – Main Harness Connector

P5 – Siren Connector

System Disable Switch (Alarm On / Off) –
(Switching between on and off should be done with the ignition ON)


Entry delay adjustment –
Minimum =5 seconds
Maximum = 15 seconds
On the top of the box in the rear right corner.
There is a round hole with an adjuster inside.

Note that the Exit Delay is always 20 seconds after arming.
#160086 by Robsey
Sun Nov 06, 2016 11:12 pm

a – Remove Glove Box
b - Attach Alarm control unit on top of the lowest shelf on the rear of the glovebox.
Use double sided fixture strips, or you can use screws if you do not mind damaging the casing of the glove box with screw holes.

a – Install siren on bulkhead above steering rack.
(Remove sound proofing on strut – On diesel variant mount on passenger side strut)
b – Use the siren and the bracket to identify the location
c – Using the siren mounting bracket as a guide, mark the mounting holes – at least 6cm apart.
d – Drill two suitably sized holes for the screws in the kit.
Before drilling any holes, make sure that there are no components which may be damaged on the other side of the bulkhead being drilled into. Double check for any wiring harnesses that might easily get damaged by a drill bit – there is a large main-artery of wiring loom across the inside of the bulk head behind / above the glove box).
e – Install siren assembly

a – Install the status monitor switch into the pre-machined switch blank in the alarm kit.
b – Fit the new blanking panel on the right hand side of the steering wheel.


a – Drill a 9mm diameter hole 30cm to the right of the driver’s side wing edge and
2.5cm forward of the rear edge of the slam panel.


a – Use original vehicle grommet, which is exposed when you remove the glove-box.
You will need to thread the wire for the bonnet contact (Pin Switch) and the Siren loom through this grommet.
#160087 by Robsey
Sun Nov 06, 2016 11:12 pm


Wiring Precautions. – Yes, I am keeping you safe from harm and tears caused by things going wrong.

1 – Read these pages several times to ensure that you are happy that you understand the work to be carried out. I would even suggest printing this all out to be totally sure.
2 – Make sure you have the codes for the radio or other audio equipment.
3 – Disconnect the battery before working on any wiring.
4 – Ensure that all joints are secure – I mean, in the 80’s and 90’s, scotch-locks were seen as a quick fix, but as many 901 owners will attest, they are not the most secure and reliable way to splice additional wires into a circuit.
It is therefore recommended that all joints should be soldered and then insulated with heat shrink sleeving.
I also find the idea of making a joint to a random wire of the correct colour that happens to be in the big bunch that runs above the glove box is a bit hit and miss.

5 – Check all wiring thoroughly before reconnecting the battery and fitting the in-line blade fuses.

From Left to Right

Requires additional Optional Module 906 or 910
Used only in conjunction with Optional Remote control Unit 903

After looking at my loom, it appears that the Brown wire mutates.
There is a big chunk of heat shrink sleeving that covers the whole loom for a few inches.
When the Brown emerges from the other side of this sleeving, it has turned into a smaller gauge Brown and Brown with White stripe pair of wires. These terminate at a two pin socket, which miraculously matches to the Brown and Brown with White stripe pair of wires in the inhibitor module connectors.

Connect to an ignition live feed in the main loom above the glove box.
(Ignition live wires in the car loom are Black)
Personally, I would find an ignition live spare fuse point in the fuse box, as tapping into “any old black wire” could over load a circuit if you happen to make the wrong selection.

GREY with BLACK tracer stripe – ACCESSORY GUARD.
Attaches via a ring terminal to rear of the radio.
If not connected to the radio, connect to a good ground for the alarm to work correctly.
I am sure that on the cavalier, Pin 1 of the radio’s ISO connector is actually for this function.
I also think that the Cavalier wire colour for this function is violet with brown tracer.
In this instance, I would cut off the ring and solder on a suitable female ISO pin and then insert this into the ISO connector of the body loom clipped into the rear of the radio cage.

Run a wire via the grommet into the engine bay, to the pin switch on the slam panel. Cable tie the wire in place.

Feed a wire along the passenger side sill, under the plastic trim towards the rear load area.
Dependent upon model – Connect to the boot lamp switch Black wire or brown with white tracer.

Connect to a Black wire with White tracer stripe in the main loom above the glove box.

Connect to a Black wire with Green tracer stripe in the main loom above the glove box.

Connect to a grey wire in the main loom above the glove box.

Cut off ring terminal and use red scotch lock to splice into the brown wire going to the glove box light.
I would find a grounding stud for this, rather than tapping into the glove box lighting circuit.
There will be plenty of suitable such studs behind the dash panel or glove box for this.

Connect to a permanent live feed in the main loom above the glove box.
(Permanent live wires in the car loom are normally Red)
Similar to the comments for the orange wire, I would find a permanent live spare fuse point in the fuse box, as tapping into “any old red wire” could over load a circuit if you happen to make the wrong selection.
#160088 by Robsey
Sun Nov 06, 2016 11:47 pm
I will modify the thread as I proceed...

I have the starter inhibitor unit coming this week and I am still looking for a status monitor switch.

All in good time.

Update - Unwittingly I lied.
It isn't a starter inhibitor, but a fuel pump inhibitor.
A very small unit identified as the 910 module.
And it is super basic to wire in...


Two fat black wires that daisy chain into the fuel pump relay wire in the main loom above the glove box.

The other is a Brown wire and a Brown with broken White stripe pair, with a two pin connector on the end.
Apparently this plugs into the 903 remote control unit; but as mentioned above, there is a matching two pin socket on the 901 loom.
So it is possible to have either inhibitor connected directly to the 901 unit should you wish not to faff with fitting the 903.

Here is the bag of parts including brown Scotch-Locks... :sick

#161439 by Metallicav
Mon Feb 13, 2017 10:58 am
Very informative and helpful writeup, my 901 has decided to malfunction, setting off the siren and not being able to turn it off was the first problem, so I had to remove it in Tesco car park late at night and in Asda carpark midday after I reconnected the unit after the problem temporarily stopped.

Now this morning on my way into college it has decided to continuously set off the hazards flashing every half a minute, making a very fun drive in, good to know there's a master switch on the unit!

Is the unit shown above one that you have purchased for your cav? if so some information on where you managed to get it from would be much appreciated.
#161442 by Robsey
Mon Feb 13, 2017 5:29 pm
I bought the 901 from ebay.
As I write this, there is a complete "Vauxhall Alarm 901" on ebay for £52.
In 1996 the dealer price for this was £286 fitted.

Mine looks like it was new, but had been raided for the status monitor.

I may abandon fitment of the 901 alarm, as I have a working Meta / Toad unit already fitted; and I cannot get a status monitor and cable anywhere.

I bought it in a momentary urge to revert everything to GM only.

The 910 immobiliser unit, I bought from Genuine Parts Search / AutoVaux.

All part numbers are in the first post.
By the way - the 902 alarm follows the number sequence above so it's part number is - 91143122

In your current situation,
(Ignore this next comment and move onto the next post)

I would check connections to the door pin switches.
Especially if the alarm is a self arming unit and relies on the opening and closing of the driver's door to set it.
#161443 by Robsey
Mon Feb 13, 2017 5:31 pm
I would also check for ignition live voltage to the orange wire in the alarm.

If this is live, then it should prevent the alarm from self arming.
#162545 by Robsey
Wed May 17, 2017 10:38 pm
I now have 1 3/4 System 90 901 alarm kits.
I bought a cheapish used unit from a Frontera A.

What is interesting is that the 'Frontera specific' installation manual is a lot more informative than the generic booklet.
The fault finding section is two whole pages.

I now have a much clearer understanding of what all the pins do.

Had I stripped the plastic casing from the alarm ecu itself, I would have noticed that all the connector pins on the printed circuit board are labeled.



I also discovered that a 902 ecu appears to be a 901 ecu but with a lot more components.
The 902 components are soldered inside the areas on the left within the dotted outline.

The entry delay adjuster is in the top right corner of the circuit board.

The System On / Off switch is in the bottom right corner of the circuit board.

The other thing I have is a status monitor and mini loom.
The only two parts missing from my original unused 901 kit.

One scary thing I noticed, is that the Frontera alarm kit had been fitted as per instruction - that is 'with scotch-loks' !!
It had been stripped out carefully - with the scotch loks still attached.
#162546 by Robsey
Wed May 17, 2017 10:48 pm
I could use the status monitor LED to give the impression that a factory fit alarm is fitted.


The LED is conected via -
Pin 1 = LED + on the Orange wire.
Pin 3 = LED - or ground on the Green wire.

Pins 2, 4 and 5 have strange initials designating manual (set via 903 remote if fitted),
Manually off - or valet mode
And Auto - sets itself 20 seconds after the last door is closed.
But at this stage, I could not say which pin does which function.



Here is the fault diagnosis tables for the 901 alarm system.





Sadly, I do not have access to the 902 or 903 modules, so cannot provide info for these.
Hope it helps none the less...

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