Preface
To all 350Z roadster owner, this is my first post on this forum and also the 350z community. Being an owner of a 2004 350z roadster, of course I experience the same frustration of various soft top problem as others. I wouldn't blame the car since it is almost 20 years old now. The car is cool and unique therefore I will not give up on it. I've got so much help from the community therefore I decide to share some thought when diagnosing the soft top problem.

Storage lid sticking
The car is bought in 2019, during test drive the top is working. After I bought the car, sometimes the storage lid is struggling, only rise for 2 inch. I will have to repeatedly press and release the top open button such that it will move a little bit every time, until it pass the struggling point, the storage lid will be fully open, then the following sequence will always work as it should.

This will only happen when I did not operate the top for a week or longer. Once the top is opened, it will close and open without any problem. Until a week later it will do that again. I search online and found some owner also have this problem. At first I think its related to the storage lid motor in the trunk because it seems not having enough power when the storage lid start to open (lay flat), which required most torque. But a further diagnostic shows the cause of this problem may varies.

Top material replace & storage lid motor rebuild
In 2020 I replace the top material with a Robbin top, since the original vinyl is harden with torn seams and leaking. I met some local 350z owner having the same storage lid problem, I help them to replace the top material, clean and replace the storage lid motor brush. After a few open close cycle the storage lid is working smoothly, at that time I believe the problem is solved. Although, a further diagnostic shows this may not be the only cause. All I can conclude is the material do not have positive or negative effect on the top operation, because the top works after I rebuild the motor with the old vinyl top, and it also work after the fabric top is install.

5th bow motor rebuild, limit switch & button check
From time to time, the storage lid problem is getting worse. The lid goes up an inch then stop. Repeatedly press and release the open button will force the lid to open a little by little, but when the lid is fully open the sequence did not continue, instead the lid motor is still forcing the lid to open, because I saw the lid want to move a bit. If I press the close button the lid didn't lowered, strangely the 5th bow want to rise but the 5th bow had already raised so it goes nowhere. Needless to said I went to rebuild my lid motor and 5th bow motor, after everything put back the problem persist.

This make me study the FSM - RF section. The motor move and stop depends on the limit switch. If the limit switch is broken, the control unit do not know what to do. Therefore I unplug the control unit and test the limit switch one by one.
5th bow fully open, top fully open, top fully close, body interference, roll bar interference, storage lid fully open - these 6 limit switch works
5th bow fully close - intermittently work, I suspect this switch fatigued because when top is closed, this switch is always being pressed by 5th bow, replace with new switch
storage lid fully close (LH & RH) - one of the switch is not working, I dissemble, clean, test and put it back
5th bow half latch, full latch and ending switch - didn't check since the 5th bow lock is working and I think it is not related to this issue.
Brake switch - work since the 3rd brake light is working
Top open / close button - work

After the limit switch is fixed, the top work once, then problem persist. At this moment I suspect the control unit is the culprit.

Control unit, battery voltage and headlight ?
One night when I testing the soft top, the top stuck again. I have no clue what to check next so I decided to leave it and wait for the next day. When I start my car and turn on the headlight, I unintentionally press the top close button and it works. Now this is interesting, the top works only when the headlight is on, and stop working when the headlight is off. This lead me to nowhere, I just cannot figure out why the headlight and soft top is related.

I have check all the related parts with the top operation. The only part I can't check would be a top control unit. Before buying a used control unit, I measure the voltage and ground at the control unit terminal, voltage is 12-14V and ground connection is good. Later I found a used control unit, tested working before removal. A quick swap with my own control unit, nothing changed. Problem is still the same.

I have been using the headlight trick for several months, one day when I turn on the headlight, I notice the rear brake light is very dim. When I press on the pedal with headlight on, 3rd brake light and the rear brake light works fine. When I turn off the headlight and press on the pedal, the 3rd brake light is not working, rear brake light is dim. It has to be the brake light switch. I use a cable to short the brake light switch plug, the rear brake light is bright and the top work perfectly. Finally this explain why the top works when headlight is on. and after replacing the brake light switch, everything works again.

 

Thank you for sharing that info.