Am about to fit one in the rear of my 90 and would like to set it up so it comes on when the rear door is opened
I have a "plunger" switch there which is part of the alarm/immobiliser set up so there must be power and wonder if I could simply tap in there without upsetting the alarm
Advice as usual would be much appreciated
No guarantee of power - it's more likely that it just provides a switched earth path. You could probably make the switch perform the dual function (possibly add a diode or two to ensure no interaction) but I think that you'll have to provide a source of power for the light.
There may be unused connections in the wiring harness intended for this purpose or something that you can hijack. The trailer permanent power connection which you will almost certainly have will be at the back of the main longitudinal harness somewhere.
No. The plunger switch is a ground closure for a signal from the alarm. You can't leverage this signal to provide power/ground closure for an interior light. Leave it well alone.
(You could notionally install a two-pole relay which would obviate adding an extra plunger, but frankly, an additional plunger would be cheaper and easier.)
You need an interior lamp that has isolated ground, so you can use a ground-closure to switch it on. If your lamp has only one wire and is earthed by its chassis, you will have to use a relay to switch it on.
You should be able to pick up a permanent live from somewhere around the back of of your 90; tap in using a Scotchlock tap connector...
So how come on my 1996 90 CSW it works as a light switch as well as an alarm trigger?
Could it be that when the light goes on it senses a voltage drop and this triggers the alarm ??
DieSea
In article , Dave Osborne writes
There's a good argument for _not_ having a door-activated switch at the back though.
I can think of lots of circumstances when I want the back door open without the light coming on. You might want to consider just having an earthed bulb holder (or fitting), and a live going back to a switch on the dash, or a permanent live to it with a switch on the fitting itself. Door switches tend to be very unreliable, and you want it to work every time you need it to. At 12V, you don't need much switch resistance to cause the light to be quite dim.
Possibly.
You confuse me with someone who cares.
As far as I'm concerned the alarm unit has been something of a problem for the past seven years or so. I'd have been happier without it, but that wasn't an option available to me when I bought it, even though I bought it new and had to wait three months while they built it.
I imagine that if you look at the circuit diagram you can see exactly what is connected to what and work forward from there.
What I am saying is that on a 90 CSW the rear door push switch operates the interior lights.
More than likely, as DieSea says. The plunger switch is already wired up to provide ground closure for the light and the alarm senses the ground closure without interfering with the operation of the light and vice versa.
However, when you start the other way round (i.e. the plunger may have been specifically installed for the alarm (and the OP doesn't say whether the alarm is factory or aftermarket)), the alarm may not be happy if you convert to the above arrangement.
Many thanks to all who have responded to my query ( this is not the first time I have asked for help and received it}
The existing plunger is part of a separately installed alarm system. I need during the shooting season the ability to see the interior when my four labradors have finished a (hard) day's work
"Working" vehicles tend to have their rear doors open for long periods leading to non-starting flat batteries when you want to go home.
Use an interior light fitted with the standard 3 position "off / on / door open" switch. It only requires a live feed and a wire to the plunger door switch (which connects it to earth).
Is that a joke?
I've left my interior lights on overnight and not noticed any change in battery condition in the morning...
His battery might have been on it's way out anyway, you wouldn't notice it with a good battery.
Sensible suggestion to feed it with a proper switch if the back door was left open all day as in a working vehicle.
I'm going to upset someone as I'm just helping to restore a Jeep! ( a proper one, like the ones I had before I had Landrovers, which don't give me any trouble either I might add). :-)
Sadly no.
When your multi-tasking farmer/builder friend insists on an 18W bulb so he can actually see what he is doing and then slings a few fencing rails in the back so he can't close the door it doesn't take too many working days (or nights) before the battery objects.
Admittedly, for brevity, I did say "working". A more accurate description would have been exceedingly hard working, constantly abused, LWB diesel vehicle that has provided sterling service for many years - and could really do with a new battery (and a few other bits!).
I wasn't referring to enthusiast owned and well cared for vehicles like ours.
But the real purpose of my post was to emphasise that a switch should be fitted, and the easiest way is to use a switched interior light fitting.
Mine is no well looked after enthusiasts vehicle, it's my main transport and it gets used reasonably hard.
On the other hand I do make sure the battery is in reasonable condition and that it's not one of those dreadful Land Rover ones but a tractor battery.
As far as I'm aware my interior lights are 2x 6W...
My 98 90CSW has a rear interior light. The rear door plunger operates the alarm, if activated and also switches on the lights. There is a timer arrangement which switches off the lights after a number of seconds (which I've never actually counted).
Its a V8i (AKA 50th Anniversary) and the alarm system was factory fit.
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