Xantia Interior Light staying on

[angle]

Apologies in advance for my almost total lack of electrical knowledge...

I have an S1 Xantia and have noticed in the last week or so that the interior lights on the B-pillar have been staying on while driving. Its intermittent, and occasionally they'll pulse on and off, but they always go out when I lock the car.

I took advantage of everything working as it should earlier to do a quick check of the door switches. The first three I tried all seemed to be working properly - light coming on when the door was opened, going off when you manually push the switch in. The problem seemed to be with the rear drivers side door - I pushed the switch in and the lights stayed on. I unplugged it - lights stayed on. Changed the two rear door switches round - still on. Except now it was staying on when I locked the car as well. Disconnecting and reconnecting the battery seems to have got it back to its previous state of the lights being on all the time the car is unlocked but turning off when its locked.

Can anyone think of anything to be checking for other than a chafed or broken wire somwhere? If its going to be that, any likely places to check? I can't think of anything I would like to spend my Sunday doing less...

Thanks for any help.

[xantia_v6]

Check the boot open switch, which is below the trim at the bottom of the hatch.

[CitroJim]

Door courtesy light switches on the S1 can cause this too... Check them for corrosion and general wear. They are standard items.