Sorry. Fuse 17 provides constant +12V direct from the battery.

Switched power (15-bus) is provided to the central locking relay through Plug O, pin 13 (BK/GN wire).

Try measuring +12V from Plug O with ignition switched on and then off.

 

Not trying to kidnap the thread, Borland, which is the central locking relay?

 

Plug O, pin 13 has two BK wires.
Plug Q, pin 13 has the (BK/GN) wire. It has THREE in that pin.

With the voltmeter, it powers on with ignition switched on and powers off with ignition switched off.

What's next?

 

Looks like the central locks control unit might need replacement.

But first... Have you said that the locks work with the key in either of the side doors, such that both doors unlock and lock together?

 

Yes, that is correct...

The locks work with the key in either side door, locking and unlocking together. Even the rear hatch will lock the side doors when the key is turned to the left.

All that works perfectly.

 

Then it must be the control unit (p/n: 928.641.602.05) is defective. It's located just inboard of the center console side carpet piece, just below the stereo head unit. That part is used on 88-95 cars, so you might find one used on eBay.

 

What else does this control unit do?

How sure are you on a scale of 1-100% it is defective? Do you know of these units failing, as in a common problem?

 

Lock functions, like you'd expect.

Sure? That's a bit hard for me to access on my end with such limited information. You be the judge.

 

Okay....

What about the central lock button panel? Is there a way to test this? How common do these fail?

 

I'm watching this thread for clues to fix mine. Mine doesn't illuminate/work at all but the doors lock/unlock fine. AC button works though.

 

The lock panel is a switch and light - if they work its not that.

The lock controllers are different by year <'89 is one type (based on the lock type). '89-'90 are different (with new locks) and 91+ are different again (integrated into the alarm/lock/interior light module).

Alan

 

Im searching, but in all the post made here ,you guys don't have a non functional looking button. My 86 does not lit the button light. Also the door locks do not work either with the key. Yesterday I did a wire check and had volts on the wires that goes through the doors. I din't found anything. My central warning unit was badly fired, I intalled one new on sunday, now I have all my lights working on the cluster. Need some help to see if I have to replace the central locking unit. Does anybody had a absolutely NOT working locks I mean anything that could give some clue??? Thanks..!!!

 

Okay, it has been a few months since this post was used. Time to revisit to see if there are any new insights for this repair. Had the car away for four months so have to get back at fixing this "interior only" central locking issue.

Anyone had the identical problem they resolved on a MY 1990? Thx.

 

Okay, here is the BIGGEST challenge yet to this problem.

With the car OFF, the light switch is turned to power on the parking lights. When this happens, the lock panel button is also powered on and works. There is no key in the ignition and no engine running. What kind of an electrical gremlin is this?

Of course the central lock button only works in the "open" position, as indicated earlier in this thread. Nevertheless, I thought this new problem might be related in some way.

Tell me I am not the only one this has ever happened to...

 

My lock button doesn't light in my 90S4 but functions correctly otherwise.