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Discussion Starter #1
Alarm Module (Large Plug)

1. Grey/Brown – Spliced Into Grey/Brown/Yellow of Green Plug (X13254) Pin 2
2. Vacant
3. Violet/Grey – To Siren Plug Pin 4
4. Black/White – To Siren Plug Pin 3
5. Violet/White (Shielded) – Spliced Into Violet/White in Loom behind Glovebox
6. Brown – To Earth
7. Vacant
8. Vacant
9. Brown – To LED Pin 1
10. Grey – To LED Pin 2
11. Blue – To LED Pin 3 & 4
12. Vacant
13. Vacant
14. Vacant
15. Red – To Live
16. Blue/Red (Shielded)
17. Blue/Yellow – To Purple Plug (X13253) Pin 17
18. Blue/Green/Blue – Spliced Into Blue/Red/Yellow of Purple Plug (X13253) Pin 4
19. Red/Brown – To Siren Plug Pin 2
20. Blue/White (Shielded). Spliced Into Blue/White In Loom Behind Dash
21. Vacant
22. Brown/White (Shielded). Spliced Into Brown/White In Boot Near Light
23. Black/Brown – Not Connected
24. Brown/Violet. To Siren Plug Pin 5


Alarm Module (Small Plug)

1. Vacant
2. Vacant
3. Vacant
4. Brown/Blue – Spliced Into Brown/Blue/Yellow of Green Plug (X13254) Pin 3
5. White/Green – Not Connected
6. White/Black – Not Connected
7. Vacant
8. Black – Not Connected


Alarm Siren Plug

1. Brown
2. Brown/Red (
Orange on some siren wiring)
3. Black/White
4. Violet/Grey
5. Black (Black/Red or Brown/Violet on some siren wiring) This goes to the bonnet pin-switch
6. Red


LED

1. Brown
2. Grey
3. Blue
4. Blue – Spliced Into Pin 3
Billy do you know what the wires that go to the siren do? I assume there is an active siren line, constant power and a GND? I want to reuse the harness for an aftermarket alarm but want to make back/forward compatible the engine bay harness signals also to prevent fire or damage by future owner/modifiers.
 

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You are right with your assumptions but I don't know for sure despite dismantling every type of siren! The principle is that the siren is active all the time and is charging the backup batteries or capacitors as appropriate. Should power be cut to the siren or the module (either by a dead car battery or the wires being cut) it will activate and will continue to sound until it exhausts it's own power source. Logically as you have already realised this only requires three wires so assuming the Red and Brown are the live and earth respectively and they have a direct feed, that leaves the Violet/Grey, Black/White, Red/Brown and Brown/Violet to do the job of seemingly a single wire! What I haven't done yet is to measure the volatage of these wires at arm and disarm, this may hold a clue to their function.
 
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