[asteiger]

Hi Folks, I had my recent fit and headaches with the alarm/security/door lock system on a 96 P38. Which also involved a myriad of misleading issues the least of which was having a disabled vehicle with no one willing to take it for a drive including me. After all half the fear is how much is going to cost in time and money if, 'Ermintrude' which is what I call my p38 decided to throw a fit and disable the engine or lock you out in goodness knows where.

So back to basics, the drivers door latches and locks.

Step one, I took out the drivers door latch and dismembered it to observe this gremlin every one who posts regarding this issue of EKA and locking accuses. It would however seem that in most cases it is the micro switches within that assembly that appear to go bad.

Step two. Tested the switches using a simple open and short continuity tester (For those of you who just want to test insitu without going as far as I did too affirm malfunction. Simply gain access to the door latch connectors. There are two on this vehicle, one 6 pin and one single black. Detach them and simply hook up the negative lead on your probe/meter/buzzer to the black wire and the positive lead of your tester to white, blue, red each in turn and operate the key to confirm a result. All mine read open circuit.

I found not only is this a common problem that plagues the fancy RR security system but one that many electronics technicians will come across. Yes simply dry solder joints, indeed the three set micro switch is prone to this problem too or perhaps our expensive microswitch was switched for inferior manufacturing during a cost saving drive who knows. The micro switch is a Cherry NM-13-0012, and apparently as hard to find as unicorn poop.

I discovered this problem by pulling on the wires to find that I got a closed circuit indication which aroused my suspicions, So in pursuit of a cheap solution after finding out the price of a latch I would not deny myself the adventure of examining closely the microswitch assembly itself.

I removed the pcb assembly filler using a small blowtorch gently applied to surrounding seal where the wires connect and are duly buried. I then simply gently dug out the softish epoxy material which took about 45 mins with a crafting scalpel. On revealing the small PCB which the microswitches are mounted on ( hidden side) I specifically targeted and cleaned carefully all the solder joints in order that I could re solder them.

I used a low wattage soldering iron gently reapplying solder to all visible joints even if there were no wires connected. Well voila on retesting all the connections worked and I had a positive signal on depressing the switches. I then gave the switch a final test before applying epoxy to replace the factory resin or whatever it is. Reassembled the lock and micro switch with refit back into the vehicle. Operating by key is now not hit and miss but works every time,and with this gremlin resolved I can now clean out and service the vehicle with a little confidence that she can be driven and also faithful.

Thanks to the forum poster/s Auslander, I believe who suggested the 7 pin connector jumper to the door module which got me out out of trouble and home.

 

[asteiger]

Lock taken apart

Extracted door motor and microswitch pack

Microswitch before cannibilizing


Start of nothing ventured nothing gained project











Ready for soldering... Sorry no more pics camera battery died.

 

[asteiger]

If anyone does try my 'fix' please do let me know if it worked for you or helped in anyway. I would like to be able to contribute positively and hope that I helped someone in some way.

Thanks.

Andrew

 

[ConradM.]

thank you for your post. I must commend you for your tenacity in going into the latch to resolve the all so familiar locked out and stranded feeling. I recently had same issue which was resolved by 'cheating', that is, I purchased a new latch. Your post helped me diagnose my problem.

 

[pwood999]

Lot of faffing about when it's easier to buy & fit new microswitches.

 

[tomcatrr]

Lot of faffing about when it's easier to buy & fit new microswitches.

Can you send a link please, where to buy!

 

[pwood999]

Try Marty_NZ on here does refurbished door latches. He might sell you some microswitches + postage ?

 

[marty_nz]

The microswitches I use in my refurbished latches are their DC series.

The biggest problem with fitting new microswitches is the alignment pins on the moulded block are ever so slightly in a different place, so you need to re-drill some holes and use something like threaded rod to pin the new ones in place.
More work, but at least you have brand new switch contacts.

 

[asteiger]

thank you for your post. I must commend you for your tenacity in going into the latch to resolve the all so familiar locked out and stranded feeling. I recently had same issue which was resolved by 'cheating', that is, I purchased a new latch. Your post helped me diagnose my problem.

Thank you, Although the fix is for the more adept or adventurous DIY'ers it is certainly not hard. I believe it is one solution of many choices. You chose wisely, maybe I was lucky but still curious to discover if any others were willing to try it with success. As in most cases the old latch is either garbaged or reduced to serving as an exopensive door stop. I was rather surprised at the cost of new while developing a growing list of other defects. So I took the opportunity to save a little money out of necessity in what still could be a money pit. It is a shame that I have an emotional attachment to the vehicle and we all know in many cases love can be so blinding.

As indicated by other posters one of whom indicated that the specific micro switches were replaceable with new, either lock or refurbished latch. I would certainly be very interested in the source of such a switch. The switches themselves are packaged in a IP rated module which does not lend itself well as indicated by Marty z to a general geometry for replacement without modification. An exposed mechanical micro switch, which may not have the IP rated qualities of OEM, would leave the vehicle susceptible to moisture. In my specific case had the physical switches on the switch contact side themselves (see pics) been compromised I would have followed your solution.

Through the process I kind of figured out that a lot of the vehicles (p38) electrical logic is simply binary voltage based. The control modules take their inputs as either a one or a zero. More modern vehicles have tolerance and variable analog decoding. Therefore on powering up this vehicle anything missing will generate a fault condition which will remain in that state until fixed or temporarily fooled into working. I recall using this model of electrical wiring for MOD/BREL engineered vehicles while working in YORK, UK, before they were taken over by ABB many moons ago.

 

[Gordo51]

i just purchased a new door latch assembly from LRdirect in the UK. Part number FQJ103250.
The door latch is a complicated assembly with many plastic parts that could wear out. You may fix the microswitches but what about the rest?

 

[asteiger]

Gordo51 ~ Your point is valid . In my specific case I examined the entire assembly including the plastic parts, were it the case that some mechanical part plastic or otherwise had been worn and was not replaceable without buying an entire assembly or part thereof. I may have indeed attempted to fix that, I kind of roll that way and if successful in solving it I would have posted what I did. If not I would have done what most will do, simply buy one. However my post is aimed at or to provide my experience to other adventurous DIY'ers, and just maybe help in a contribution to other ideas or sources for specific parts of the lock mechanism. Common sense would dictate evaluating the time and cost factor. Making a plastic part takes a lot of patience with specific resources and more importantly many of us have better things to do.

 

[marty_nz]

The DC-series switches I use in my reconditioned latches are all IP rated, as with the original ones. The only fiddle is having to pin them in differently as the moulded version have different mounts. But it's not too bad when you've done a few of them! (probably done 40-50 now over the years! and have another 30 odd here in bits)

I also fit a higher current rated switch for the RHF latch CDL switch as the tailgate motor grounds through it, and has to handle a higher current than the other switches.

Plastic parts broken... again for me it isn't a problem! I have many more latches than I can rebuild, as so many of them come in with burnt out motors, and since these aren't available separately, means I end up with LOTS of spare parts!!

Good work on repairing an original set though - I couldn't be bothered digging out the epoxy - half to the ones I see have mechanical defects with the switch aswell, so make my decision to just replace them easier!

 

[John949]

Old thread I know but anybody reading it might be interested in my solution to fitting new micro-switches in the latest type lock. You can get suitable switches from RS

https://uk.rs-online.com/web/p/microswitches/2945905/

I didn't fancy my chances of drilling new holes in the casing in exactly the right place so I used a distance piece instead - see below:

First I joined the three switches together using their mounting holes. the shank of a 2.5mm drill is a nice light press fit. Then I soldered the wires to the sides of the terminals as shown below. This allows the switches to sit squarely on the terminals.



The white square is the distance piece designed to fit under the switches and hold them at the right height. It turned out to be exactly 3mm thick.



I used some double sided tape to hold the spacer during assembly and some more on the sides of the switches just to hold it in the right place during assembly.




Here it is with the microswitch assembled.

Working well so far. BTW when searching for something to make the distance piece, I started looking at my collection of steel sheet. Took me a good thirty seconds to realise why this was a very bad idea. I ended up using some uPVC offcuts - very easy to work and doesn't split or crack.

 

[marty_nz]

Pretty much identical to what I do in my refurbished door latches.

Except I pin the switches in with M2.5 threaded rod, to stop them from being able to move in any direction. I also drill them through into the mounting where the motors are and also then into the casing. It isn't too hard to get the holes in the casing in the right place to hold the other switches in, but nice idea on the spacer at the bottom.

Is there any side-to-side movement of the switches when sitting in there?

 

[John949]

Maybe a little side to side movement but I used some double sided tape on the outside of the switch block just to make sure everything stays put.
As luck would have it I got a problem with the passenger door not registering closed shortly after I did this. After taking it all apart again to see what I had done wrong it all seemed to work fine in my hands. I think the problem was actually the setting of the door catch which was not allowing the lock to rotate fully when the door was closed. Anyway I moved the catch outwards slightly and it all seems fine now, also it requires a far lighter pull on the handle to open the door.

 

[annette]

I have to say that I am very thankful to both asteiger and Marty.
Yesterday we had to take two latches apart to fix a latch I bought from Marty.
It was damaged by a badly repaired door handle .. well I was not too pleased. Tried to rob a microwitch of the probably only RHD door latch in the country that I bought for bits.. but it had different switches .

Sigh.

Well it is nice to say

Lot of faffing about when it's easier to buy & fit new microswitches.​

Try that in Costa Rica. Everything that is not a Fedex order at 450 USD shipping costs takes absolute ages to get here by mail etc.

You certainly can't just go and buy a bit fat condenser for you Engine ECU here and even less a microswitch..Somebody is going to send me the condenser from Brazil.. so anybody feeling like sending me a microswitch to a friend in France who is coming for a visit could certainly earn some money.

I am thankful, again, for any wisdom shared here