Battery Immobiliser

[terry randall]

My 91 SE seemed to be suffering from flat battery syndrome. So I checked boot light & interior light first of all. Both OK. Tested battery to find a steady 1/4 amp loss. I guess it's the electronic immobiliser. So to avoid disconnecting the battery all the while, which is awkward where it is, I bought a 12V/24V battery cut off switch from ebay ( robust turn key type, but only £4 odd ). This I located behind drivers seat above the speaker box. The terminals go into the bottom of the battery compartment. I cut both negative leads ( I found the 1/4 amp was happy to use both leads if you only disconnected one ) and reconnected to the switch terminals using crimping rings you can get from a motor shop. Now, I just turn the key behind the seat when i get in and the reverse on leaving. All seems to work fine and no flat battery problem. I could now probably ditch the electronic immobiliser as I remember one that I had on a VW Corrado that was a real pig till I disconnected it!

[GeoffSmith]

As you can obviously wield a meter and are versed in the black arts, check out the fuses and pull them until you find out what is draining the battery. It would be a shame to pull out the immobiliser and find it's something else!

[terry randall]

Thanks Geoff, was only joking about pulling out the immobiliser, I don't think the insurance people would really like it. But this one on the Corrado used to immobilise itself for about 1/2 hr. before it reset itself again. I even replaced the starter motor before i realised what was going on ! Yes, I will pull the fuses just to confirm where the drain is as it could indicate some other problem (surely not on an elan! )
Tel

[rip]

it could indicate some other problem (surely not on an elan! )

Indeed, surely not

[terry randall]

Checked, and indeed was immobiliser. I've inherited on of those 90's key fob types and, if i remember correctly, if basically fitted a relay isolates the car and the coil on this relay is what drains the battery. Now its only 1/4 amp but as you remember from your school physics, at 12v that's 3W . Now a good well charged battery should cope for a week but when the cars not hurtling down the country lanes with the top down on a summer's days and the weeks roll on, then hey presto, flat battery! Now I only suggested the isolation switch as a cure all for those less electronically challenged owners. My No.1 SE would not be subjected to the indignity of a hole cut in her battery compartment as she is too original and pristine for that sort of treatment but there again, she does have a new proximity switch type immobiliser with no flat battery tendencies. However, I digress. I think that a second relay to control the first relay will cure the drain problem if your immobiliser does the same. Or you could use one of those solar battery chargers that connect to the cigar lighter socket. I'm not sure on short dark British winter days how well they work? I heard of a Battery Brain that cuts off the battery before it drops below a certain voltage so that you can just get it started. Perhaps others also know of ways to avoid this problem rather than renewing an ageing immobiliser.