Hi@all,
a friend of mine with a P38 (LHD) has told me, that he has the dancing door locks syndrome.
After some research I found three possible routes: 1) a broken wire which touches the winding mechanism of the window, 2) a micro switch in the front(?) door locks (can it be one rear also?) or 3) an error in the BECM.
Obviously 1 means pulling the door cards, wire contact should be visible
2) How can I check / find out which door lock causes the trouble or change them both anyway?
3) Any hints or tips how to check / rule out the BECM without first installing new door locks and finding it out the expensive way?
As it is LHD and the rear tail gate button is sometimes stuck is this caused by the door lock or just coincidence?
As far as I know the RH door lock controls the rear tailgate button, but as the dancing door locks are intermittent and sadly it did not happen, yet, when I was with the car, i can not correlate.
I have the RSW suite and a Hawkeye for diagnostics.

Any hints and tipps are highly welcomed!
Thanks in advance
KCR

A quick and dirty way to see if a particular door latch is having issues may be to open up each door and see if the dome lights come on. If the lights don’t come on, that may point to a problem on that particular door or latch assembly. On mine, the micro switches on 2 of the doors are slightly “lazy” and the dome lights don’t come on right away (or sometimes I have to give the latch a quick smack!). No locking issues to date but I keep watch for any other symptoms.

First,
It will not be the Becm. It is waaaayyyyy too common to leap to the conclusion that the Becm is at fault.
At the top of this very forum you will find this:
https://rangerovers.pub/topic/5-info-front-door-latch-tests

It is a comprehensive test procedure for this problem.
The tailgate push button intermittently not working is a symptom of the RH latch having an
intermittent issue, as the power for it runs through this one.

BlackSpeed66 ... Good q&d test! THX

The door latch test is another good idea, forgot that's (t)here. THX Bolt
But will it show intermittent function? Or is it a "shotgun" approach? I have not yet seen the door locks dancing on this car, but the owner is reliable and has reported without asking ...

About the BECM, I doubt that as well, but it was mentioned at the island4x4 ordering information for the door locks as a common fault. I have checked the prices for the locks, just in case my friend says order them and install them, we will see if they are the cause. He is a little short on time.

If you have issues with the tailgate aswell, then that points towards the RHF latch as the motor grounds through there.

Dancing door latches can only be triggered by the CDL switch (central door locking). They are only fitted to the front latches, and it's the one used for tailgate aswell. The other switches (in every latch) is the Door Ajar switch to tell if the door is open/closed, and in the driver's latch there is a third, key switch to tell if the key has been turned in the lock.

I wrote the latch test sheet originally, and whilst it will tell you instantly if there's a failed microswitch, it's intermittent then it might show up as working some of the time. As well as continuity on the CDL switch, I would check it on resistance as sometimes it will show up as having continuity but as a high resistance, which causes issues too. Also it's worth when checking it, moving the sill locking button and seeing if the switch changes state before the mechanical part of the latch does. If it shows it's locked or unlocked before the mechanical clunk in the latch happens, then that causes the jumping.

The older vehicles were prone to burning out door latches, which was generally due to RF interference confusing the BECM it would then constantly lock the front doors and that would burn the motor out. That wouldn't show up as a dancing lock issue, but more the latch not operating with the rest off the remote or key in the door/LH sill button (in your case)

My bet is it's the RHF latch.

I'd also go with RH Front latch too. When the locks start to dance you sometimes find that only 3 of them do, the one that doesn't is the one that is faulty.

Latches on 94-01 cars are the same as fitted to the MG F and, as LHD cars are pretty rare in the UK, Rimmers have latches at clearance prices. RH https://rimmerbros.com/Item--i-FQJ102281PMA and LH https://rimmerbros.com/Item--i-FQJ102292PMA

Great responses from all, they will help me a lot.
THX!
I will update as soon, as I get my fingers and tools on the car.
best regards
KCR

BTW … it was, as suggested the door lock. We swapped both front locks and the phenomena disappeared. Funny enough it happened predictable at 23° C … an error with a threshold ;-)

When mine did it many years ago, it was only in hot weather and I put it down to thermal expansion. Now, the keyswitch on the Ascot drivers door doesn't work but only in cold weather so there is definitely a temperature element. A combination of wear and fine tolerances I suspect.