Robin Allum - Fitting a security immobiliser to my 1956 DB 3 Litre
(This unit will only fit negative earth cars)

I have been concerned about the security on my 1956 DB 3 litre; there can be a problem with cars at shows being stolen as it is so easy to start a lot of classics. I have used a wire clip in the past to bypass the ignition switch. A secret switch to cut off the fuel supply could prevent the car being driven away and I used this ploy on my 1966 Jaguar 3.8S and found that it gave me some peace of mind when my car was unattended at shows. My other Jaguar, a 1975 XJ6 S2 had a full alarm system which could be a problem once activated: the bonnet could not be left open at shows. I know that not many people would want to take a Jaguar XJ6 S2 but the engine was a bit special and quite valuable.

If a determined thief is after your classic, then nothing will stop them. So the thing to do is to make it as difficult for the opportunist; a simple hidden switch is okay but I have forgotten about it in the past whether off or on. This is not for the purist: my car has modifications so this does not worry me. I came across an immobiliser that has a tag that fits on the key ring. This activates an immobiliser relay when it comes in close proximity to a detector coil. This will only work on NEGATIVE EARTH Cars and as I have converted my car to a negative earth this is not a problem; have an alternator and modern internals in my radio. Also, I have installed a more modern Ford 3 litre Essex 6 cylinder engine. Without this engine my car would not be on the road.

A Falcon Predator Mk 2 immobiliser is a small black box that I fitted under the dashboard and the fuel pump, coil and starter push are all immobilised by this device. On my car, the coil and fuel pump cables connect at a junction behind the centre of the dash. They are white cables that connect to a terminal post. I fitted an extra fuse box at this point for the coil and pump and for any other circuits that may want fuse protection. The white cables are easy to follow. One goes from the main loom that passes through into the front of the engine bay, it is the coil cable. Another goes into the engine bay and then down to the rear of the car; that is the fuel pump cable. It is just a matter of pulling these out of the 4-way connector and connecting each to the pairs of cables of the control box. A negative cable connects to a convenient body screw. The rest of the cables connect at the switch cluster. The starter button has a small link from the fuel reserve switch. This was removed and the control box cables connected in its place. A 12 V positive cable is connected to the auxiliary plug live connection. An ignition supply connects on with the white cable at the ignition switch and the door sensor cable connects to the map light switch. A LED needs to be mounted and I found a small gap at the top of the dashboard where it meets the A post screen pillar; it just wedges in by the furlflex around the door. A detector coil hangs up behind the dash by the ignition switch.

I found that the system was easy to fit but the makers do offer an installation service which should be used if an insurance company requests a device being fitted.

Using the immobiliser is simple providing it is used within 20 seconds of the Key tag being detected; if not just move the tag away and then return it. There are no extra cables in the engine bay and everything is hidden and I have less to worry about when the car is unattended at shows.

Immobiliser control box fitted to bulkhead timber.


New fuse box fitted for extra protection to fuel pump, coil & alarm circuits.
Looms that have the coil and fuel pump white wires behind the centre of the dash board that join in 4-way connectors, then up to the terminal post. This car had been rewired by a previous owner so it is possible it is not as original but using the wiring diagram all appeared as it was intended.


Warning lamp fits between furlflex and the dash.


The components including the metal box covers the control unit.
The transponder coil hangs behind the dash by the ignition switch.
All the cables on the unit are black with white printed identification on the tip so put on temporary labels once the cable has been identified as they are soon lost when cutting to length for final connection. Remove all identification after installation.


Robin Allum