Fitting immobiliser/alarm, help

Hi all, I am looking at fitting a tracker/basic alarm and could do with some advice

I have a 1991 Cruising Cabin camper 2wd with a 2.8D 3L engine. I'm looking for stuff to cut into to immobilise the vehicle. The 2 normal candidates I guess are the fuel pump and the starter motor, the device I have has a 'relay' that can be fit into the live feed and prevent the wire going live (I think that's what it does). But I think my van has a mechanical fuel pump, so there might not be any way of 'immobilising' that, but I think I've found the location of the starter motor relay, according to diagrams, high up in the passenger side of the dashboard - so I think that is my best option for immobilisation, any reason not to use the live feed to that?

I can also use the device to monitor door opening and my van does have a display on the dash which lights up and indicates which door is open, so, and this is a long shot, can anyone help identifying those wires? Anyone done something similar?

Thanks in advance

Mart

Another question, what stops the engine when the ignition is turned off? What is the van stopping or no longer doing? I'm not familiar with mechanical fuel pumps or these old diesel engines. If there's no relay or electrical input for the fuel pump, then it's not obvious to me how it stops pumping fuel, so maybe there is some sort of electrical switch on the fuel pump to stop it/allow it to flow? Or a fuel pump solenoid perhaps? If so, where is it?

With my tracker I can send it a signal to tell it to stop the car - handy if you are looking it unexpectedly disappearing down the road...but I need to find something for it to be able to switch off.

The front and rear door lights are on 2 different circuits, combined via a diode for the dash warning lamp.
Easiest access is via the light assemblies themselves IMO.

The engine shuts off on mine via the spill valve, but that is a PWM controlled item. Perhaps it may be easier to sabotage a sensor (i.e. simulate overheat) to get the engine to shut-down but I'm guessing.

For diesel you can buy fuel cut-off solenoids that may be the best way to disable it.

Cheers GPW. I've given up on being able to immobiliser the vehicle while running for now, although I haven't finished fitting the tracker. I have been able to use the starter motor relay as an immobiliser, at least that would immobiliser the vehicle once stopped and also should stop the van being started in the first place as long as I'd remembered to set it. Trying to get at the wires behind the dash is a proper ball ache, no fun at all!

It might be worth either adding a secondary wire to the door switches it at least trying a bit more to see where they route through. That said, the tracker has a motion sensor which seems to respond pretty well to the weight of a human getting in the van - a door being tripped would be a bit better though.

MartW wrote:

trying a bit more to see where they route through

The switch wires go right to the lamps. The lamps always have +12V, the switches just ground one end of the bub so it lights. So pop off the front lamp assy next to the rear mirror and the big dome lamp in the center of the living area and find the wires there. Then just feed via a diode both sources to the alarm.

Assuming it's like the Supercustom of course...

I hadn't thought about the fact they must go to the lamps! I'd assumed they must go to the dash in some form since there is a display on there which lights and shows when the front doors, side sliding door or rear door opens -but the wires under there are very tight and difficult to get at usefully.