before you start spending money on parts -close the top manually and see...open and close after it..
Ivan

I did try this, did not work. Interestingly, once latched closed manually, the open/close button was able to run the latch motor to open the top back up again. But when I went to close it, it again stopped at the latch point and would not latch close.

I guess this proves that the latch motor/relays *do* work, and so does the cab top ECU?? So then what's the problem?? hmmm

just one thing -try to close manually and just unlatch the front from the windshield -do not open all the way ..would it close back?
Ivan

Okay, this was a great idea. New information!

If I bring the top to the latching point, then *manually* close each latch about 20% of the way (15 full turns) by screwdriver, *then* press the top-open switch just slightly, the latch motors will open the latches just slightly. Once this happens, pressing the top close buttons will fully close the latches all the way!

Now, the thing is, if I try this trick of starting by partially manually closing the latches, and then I use the button to open the latches all the way back to fully open again, instead of just a tiny bit, it will go back to its previous state where it won't allow me to use the button to close the latches again.

SO what we seem to have learned:

-The latch microswitches work.
-The latch motors work.
-If I can get it into the correct state (latches slightly closed manually), the latches will open/close. But once the latches are fully open again, I can't engage the latch motors anymore...
-The cab top ECU seems to be operational? (FWIW my module was replaced with a 993 version about 8 years ago)

So then... what's causing the problem?

I have the feeling there's another signal being generated in the system somewhere, other whan the latch microswitches, that we're not accounting for. Is there a signal that the latch motors send at fully open vs where they start to engage? Maybe that's not tripping properly (i.e. at fully open the latches are "'too open")?

EDIT:

I did some reading and found that the latches do have internal microswitches that tell the ECU when the latches are fully open vs. partially or fully closed. When those microswitches are fully open then the ECU knows that it can run the main top motor to pull the top back. These microswitches seem to work by the fact that if I start with the latches closed, then open them, the main motor will run once the latches are open. So these switches seem to work.

It seems like everything works EXCEPT for the the latch motor running to close the latches from fully open. But *WHY*??

EDIT: Nevermind, I tested both latch microswitches. No continuity when open, continuity when closed. Seems like they're both perfect. So this really is a headscratcher? Every individual component seems to be operating as it should?

DEFUNCT ORIGINAL POST:

Oh, I have a theory:

Perhaps the latch microswitches AREN'T working. What if the ECU only looks for the latch microswitch signals in order to START the latch motors, but once the latches have started to close and are in the "mid opening or closing" state, the ECU knows that, and doesn't look for the latch microswitch signal anymore in order to continue operating the latch motors?

I should test the latch microswitches...

Bump. Anyone have an ideas or suggestions given what I've described?

I have spent a lot of time messing around with the cab top and thankfully its working great now, but I have had to troubleshoot many different scenarios. While I don't think its relevant, you could check the white limiter switches that are hidden behind the right rear speaker.

The reason I don't think its causing your issue, is that in my experience, the point of these switches is to completely stop the top from moving at all if it hits the limits of either too far open or too far closed. Its like a fail safe to prevent you from catastrophically breaking the top.

But I just thought I would mention it because its easy to take a look. The right rear speaker cover is removed with one screw and a plastic fastener (at least thats how it works on an 88 cab)

Bhom, I am experiencing somewhat the same issue you are with one of my latches. Actually, the latch will not stop - so the microswitch is not engaging. I am going to take the latch mechanism apart (like Frannie & Heidi video) to see whats going on internally https://www.youtube.com/watch?v=VMnGfM3I-Xw

Thanks for the suggestion. I've already checked those limit switches out, they both seem to work as they should :/

Solving cab top problems are sooooo simple to solve, when you watch the relays (#13) & understand what's happening.
The link in post #3 explains how the top functions.

Read the references, or just keep guessing!

Yes, I did read your references and try what you suggested. I can only get the two right relays to move (and hence the latches to operate) in two conditions: one, if I partially close the latches and then engage the top open button, OR if I unplug the plug under the leftmost relay and then plug it back in and then engage the top open button.

Doing either of those two things will then allow me to operate the latches to fully closed. But once the latches become fully open again, I can not operate them again until I partially close them again or unplug and replug that leftmost connector again.

Again, I have verified that the limit switches behind the passenger side panel are operational, as are the two microswitches in the latch frame that tell the ECU when the top has reached the windshield and it's time to latch.

Does this guarantee a bad ECU? How can we rule out the microswitches that are inside the latch motors?

Yes, it's as simple as that! If you designed the system, wouldn't you design it like that?

No! By doing the test with top in the vertical position as described in link (post #3).

Yes, I have tested all the exposed switches with the top unlocked. All of the switches themselves seem to operate correctly (open and closed circuit when open/closed). The only thing I'm not sure how to check is the SL/SR signals since they come from the latches themselves. But operating the latch microswitches (that send ZL/ZR) are working, although the right most relays on the cab ECU don't open/close with the opening/closing of the ZL/ZR microswitches.

Again, if I disconnect the cab top ecu's left most connector and plug it back in (or partially close the latches via screwdriver), I can operate the latch motors once, but once they open all the way again they go back to being unresponsive in all situations.

You need to study this from; https://www.systemsc.com/problems.htm


Cab Top - The Porsche cabriolet top (Porsche cab top) ECUs used in the late 911SC thru the 1998
993 have reliability problems the result of intermittent circuit boards also. As with the Porsche cruise
controls, the mounting of this ECU resulted in vibrational stresses being applied to its circuit board.
The intermittent unit generally caused the cab top not to lock/unlock properly, e.g. requiring multiple
depressions of the open/close switch. Also, an intermittent wiring harness which bends at the top frame
can be problematic. Additionally, the locking motors must each send a non-grounded signal (SL/SR) to
the ECU at the completion of a lock or an unlock cycle, or the opening/closing operation will fail and
in some cases may require multiple depressions of the top switch to fully lock the top in the closed
mode. If the locking motors incur any binding or are not aligned properly, the internal brass gear may
break. The switches, ZL/ZR, close (ground signal) when the cab top reaches the windshield to activate
the locking motors. With the cab top unlocked and the ZL/ZR switches taped closed, the locking motors
can easily be checked for locking and unlocking. Once the top is in the middle, it should move up
or down independent of the SL/SR and ZL/ZR switches. In this position, the UP & Down limit
switches and the SL/SR & ZL/ZR switches can be easily tested with an ohmmeter, and the complete
functionality of the cab top simulated/tested. Furthermore, the oil pressure switch (P, 964) and the
additional hand brake switch (Hd, 993) inputs must function.

AGAIN
Have you troubleshot the cab top ECU in the vertical position? If not you're still in the guessing mode.

Yes, I have read that and tested the top mid opening with the ZL/ZR switches closed. I can not get the latches to operate that way. Whether it's completely "vertical" doesn't matter does it? With neither of the passenger side limit switches tripped, and the ZL/ZR switches pushed down, the locking motors are not operable. This is the test that you're describing as far as I can tell. Am I missing something?

Will the top go forward/reverse, if you release the ZL/ZR switches? If not, then you have a bad control unit!
If you hold both ZL & ZR closed and you operate the up/down switch & the locking motors don't operate, then you have a bad control unit, bad locking motors, or both.

Yes, the top will go forward/reverse if I release the ZL/ZR switches.

Through my testing, it would appear that every aspect of the top's control seems to function correctly *except* the fact that I can't get the latching motors to operate when the ZL/ZR switches are pressed (and I have tested both of those switches to make sure that the switches themselves are working via continuity tester).

Again, the only way I can get the latching motors to work is one of two things:

1) Bring the top to closed position (which presses ZL/ZR naturally), use a screwdriver to partially close both latches manually, and *then* operate the switch.

2) Unplug the leftmost connector on the cab top ECU and plug it back in.

using either of these tricks, I can use the switch to operate the latch motors until I completely open them again. Once they're completely open again, they will refuse to close, even when ZL/ZR are pressed in.

Does the fact that I can trick the locking motors into operating in those two ways clarify whether or not either my ECU or the motors themselves are okay?

Then the timing is not correct for either/both locking motor switches (SL/SR)
in the locking motors.

Yes this makes sense that SL/SR (either how they're being sent to the ECU by the locking motor switches, or how the ECU is receiving them) is the issue.

What do you mean exactly by timing, and can I troubleshoot this further?

The micro-switches (SL/SR) opening/closing need to aligned to the gears inside the motors. The controller/processor in the control unit checks this and stops ops if the timing is off.