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No response from top motor

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Hello all, haven't posted in a while, no issues, though read digests daily!

Helping a friend work on his 1999 Boxster and we have an issue with the top not working.

The top worked last year when we put a hardtop on and we have just put in a non-blown motor to get this $3500 POS running again.

This is what we know.

1. When unlatching the top the windows lower.

2. Removed motor and switch for clamshell, switch works properly and motor will run on the bench with 12v direct.

3. Both fuses are ok, and we have power to both fuses.

4. B pillar mico switch works.

5. Parking brake light works properly

6, Top control unit will work in my car, my top control unit will not work in his.

Noticed on electrical diagrams that the control unit ties into the alarm system.

The remote works properly, doors lock, alarm works, proximity sensor works and zone indicator works, beeps if area not closed.

What are we missing.

This thing is bumming me out.

We installed another engine, which went well and it stated first try, top is the last thing to fix.



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Yes, #5 relates to that, have done searches and can not figure what I am missing, that's why I questioned the alarm system although I haven't read anything that brings that into the equation, but on the diagrams it is tied in, the question is to what extent and if that may be an issue.

Can't seem to find a trouble shooting flowchart for this system yet, there should be one out there somewhere.

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Also, judging from your description of the symptoms and the results of your tests so far, I'd say there is a good chance that the problem may be in one of the two microswitches that are found INSIDE the latch assembly.

There are two microswitches in the latch receptacle assembly. There is one on the left side of the assembly (has a large plunger that juts out when the latch is open). That one controls the 4" window drop that occurs immediately when you pull down the latch to open the top. There is another one on the right side of the assembly, and that is the one that activates the convertible top double relay.
My guess is that the latter switch is faulty, even though it may appear to be intact when you visually inspect it, and sometimes even when you test it with a multimeter. Specifically, take a close look at the solder joints where the leads attach to the plug. This can be hard to detect, so check it with a magnifying glass for hairline cracks in the solder joint and for corrosion. If necessary, heat up the connections with a soldering iron and flow a tiny bit of solder onto the suspect joint(s).
Believe it or not, the temperature (sun light, A/C blowing on it, etc...) can affect it to the point where the connection is broken and then re-established.
To gain access to the microswitch you have to remove the latch plate at the center of the windshield frame. Pop out the two little black plastic "eyes" by carefully prying them off with a very small flat blade screwdriver or borrow one of those "orange sticks" that women use on their fingernails to pry them out. Remove the small torx bolt that you will find under each one of the two eyes. Remove them and then pull down the latch plate carefully until you can see and access the wires for the switch and for the light. Unplug the wires and the latch plate will come off. You will find two fragile retaining clips that attach the switch to the underside of the latch plate. These are easy to break, so use a pair of small needle nose pliers to pull them off, very gently. You can reuse these if you are careful by squeezing the cross sections that are located at the center of the clips until they are flattened.
Also double check the two fuses again (even if you have already visually checked them) by using a multimeter there as well, as one of them also provides power to the double relay.
If none of the above yield a culprit, test the electric motor again to make sure that there are no "dead spots" in the motor by spinning it around a few degrees at a time and the applying the 12V each time you have turned the shaft/armature a few degrees.
Regards, Maurice.
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Maurice, here is the update on the top, the checklist was a lifesaver!

You were right, it was the micro switch that activates the convertible top double relay, there were micro cracks in the solder at the pins on the cross strip, so we re-soldered them and still could not get it to work, there was still a problem within the switch itself on the ground side and it would not make a connection to the socket at the relay, so we replaced the switch and everything works as it should.

What a test! After trouble shooting it all, it finally makes sense how all of the switches tie together. What a learning experience!

Thank you so much for your help on this issue and I hope that others will find this thread helpful WHEN they have a top problem, as surely they will!

This forum is the BEST! :thumbup:


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  • 1 year later...

Glad I found this as i will have to do the same check list. used the car last week and the top operated perfectly fine. Today, go to operate the roof like normal, brake engaged, engine on, pull the release lever, the windows drop and then go open the roof and nothing. No top motor sound, no warning light on the dash the latch is released. Nothing.

I will start with the fuses and go from there and then start checking the micro switches. I'll let you know how it goes.


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