Topic

This morning quick drive across Bodmin Moor to do some shopping, all ok. Half way there the interior lights came on. Opened the drivers door while driving slowly and made sure it was shut and the lights went out. All good so far.

Parked up to go shopping and locked the car, just got to the front door of Tesco and the car alarm went off, walked back to car and interior lights on again. unlocked with fob which silenced the alarm then re locked all good again. Drove home from shops interior lights on again and now the car will not lock without the alarm going off. An unlocked car is not the biggest problem in Cornwall in the winter but not good if I go anywhere populated.

Reading the posts and Google the suggestion is that it may be the drivers door lock but some have also said Pektron Relay. (I have replaced the intermittent wiper one already) Happy to buy the Door Lock from ebay but not 100% sure this is the problem.

If anyone could throw some light on this I would be very grateful.

Starting with the basics - is the car a Lucas or a Pektron car?
Did you not replace all the relays while the BCU was apart?

First port of call would be the micro switch in the drivers door lock.

As James says the first checks are the door lock switches/key rod & sill button linkages, while the door cards are off lubricate everything liberally with spray grease, especially with all the rain we have had.

I think it unlikely to be an SCU/BCU Pektron relay as they don’t give intermittent problems, the wire breaks on the relay’s induction coil and that function just ceases to work.

Another area to check if it’s a post MY03 TF is the chassis to boot lid wiring as the boot latch open signal (ground) will also switch on the interior lights, this bit of flexible harness wiring is the cause of many electrical issues (even harness fires) and if you have not checked already it’s well worth opening up to take a look, the harness design is far too short and the cores fatigue and touch internally.

The boot harness mod is well worth doing, I cut my boot harness out at the chassis end and fitted a new 7 core cable with a pivot loop at the boot hinge and a plug at the chassis harness end in case I ever need to take the boot lid off.

Thank you both, I had not thought of the boot harness. I will check that first at the weekend before buying a replacement door lock.


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I recently had a issue with interior lights stuck on,the pointers discussed are worthwhile.
Also i have come across more than once, the drivers sunvisor as been renewed and the fixing screws that hold the drivers sun visor in place can snag on the wires behind it that powers the rear view mirror lights.

The footwell lights and ignition barrel cylinder red circular illumination normally stay on at the same time.