Injector fixed - but no lights!!! back up alarm wailing...

[age]

OK - v excited about fixing the injector - now from way out left field, went out this evening and put on the headlights - NOTHING!!  And the back-up wailing alarm (not the wake the neighbourhood blast you get when the cat jumps on the LR roof at 2 AM) instead.  She runs fine - apart from 5 miles on hazard lights....  All other electrics seem fine - indicators, horn, wipers, interior light (no dash illumination tho).

Turn off the headlamp/sidelight switch - alarm off, but still no lights of course.

Very strange.  We had the injector harness separated, but clearly safely back together; fuel filter off so disconnected the block on that, but water sensor and fuel pump clearly working OK.

I've pulled the connector off the back of the horn - usual 'chirrup' - then back on cleanly.

Help!  Any ideas gratefully received.  A  2001 td5 Defender btw

[age]

Update - identified that it is the back-up alarm wailing, usually indicating that the battery has been disonnected (although this should be constant rather than just when you turn on the headlights???)

Only thing I did was disconnect and clean up the starter power supply........possibly identified the same by the 'system'?

Anyway - I've reset the alarm using the 'key and door' code; 'synchronised' the key fob using the battery out/in and key/press 4 times technique;  I've actually disconnected the battery using the handbook key on/off disconnect in 15 seconds, AND the simply whip it off and let the back up alarm sound (it didn't....).

All to no avail - everthing runs fine, but no lights and the light switch sets of the back-up alarm.

Oh, and setting off the 'real' alarm opening the door when armed, also only sets off the back-up, not the main alarm.

Stuffed - help please anyone.....!! A

[age]

Continuing this exciting replying to myself thing....... just in case it happens to anyone else!

It was the 'lights' relay in the fuse board on the interior bulkhead, nothing in the alarm circuits at all!  Clearly has something to do with the back-up alarm sensing the original disconnection of the battery/starter, but then completely unrelated failure of this relay (untouched in any of the recent work) led to this odd back-up alarm when turning the lights on.......  Good old LR!

Now have 'day and night' driving available.  Cheers, A