Electric trunk lock issues

[Orchid70]

HI

Swedish S80 from 2002.
Issue from start:
Boot wont lock at all. Always open.
I checked the electric button: it showed 0 resistance when I push the button and infinite resistance when I release the button.
I took out the lock assamble. And could find out that inside the lock, inside the servo motor, the stainless spring that is supposed to bring back the servo arm was totally rusty.
See the peace I'm talking about at 5:23 on this video (he is holding it in his left hand):


So I bought secondhand assembly, checked it with electricity so it worked and put in.

At first nothing happened, but it started to work after some fiddeling, both with remout control and with the button on the car!
So I put all togeter againg...
And day after when fixing some other stuff on the car (the electric window had gone into peacies and the freewheel on the alternator had jumped out so the alterantor, belt and belt tentioner is beeing changed) and all of the sudden - the interior lights won't go off. And of course - the trunk lock did not work again! This time - the lock did not open! Only with the key. (I forgot to check with the remote control).

I did look at the opening button and it had a simple electric switch that looked OK. It gives the same results on resistance measuring as the same kind of switch inside the lock assembly - the one that is controlling the central locks from inside the boot lock assembly.

Does somebody have any idea what I'm missing, doing wrong or where I nead to start searching the fault?
The side panel on the drivers door is dismounted at the moment - could that make some problems?

P.S. I have found out that the servo motor inside the boot lock is the same as in VW centrallocks in the boot!! So I'm fixing together the old Volvo lock assembly with a spare motor from our Passat... =) And bought one from China as well (before remembering I had the spare - in the Passat...) I could take some pics tomorrow.

[ThommyKent]

On my 2000 the trunk lock relay was bad

[oragex]

I would first make sure the alternator and battery give the correct voltage and start from there. Also check the alarm siren (or disconnect it). Electrical issues can trigger other systems to go wrong.