Very Basic Fuse Questions

[megerian]

While I am well over 10 years into my ownership, I still feel like a novice on all things electrical, so bear with me on these basic questions.

For about the 10th time, my cabriolet top stopped working. There have been a variety of reasons the other times, and a few times it just magically started working again, but this time I have verified the limit switches aren't tripped, and my normal troubleshooting hasn't solved it yet.

So, that leads me to fuses. First question, if you see this picture below , this supposedly is the dedicated fuse for the cabriolet top and yet I have no idea how to open it. I have tried prying it, twisting, pulling. Is there a secret to opening it and seeing if the fuse inside is blown?


Second question, I have a multimeter and a continuity tester, but I really don't know how to check each fuse in the fuse block. I can use my simple tester light and touch the + and - terminals of the battery and see the light come on, but I dont get anything light up when I check the fuses. I know, dumb question, but other than visually checking the 25 fuses, whats the proper method to check the continuity? Do I test before and after the fuse?

Note that a few times I have had other electrical issues (fuel pump, etc) and just wiggling the fuse resolved it. This seems to happen more often when the car has sat for a few weeks (or perhaps that's my imagination) but sometimes the fuse isnt seated properly.

[fintstone]

If you are talking about the white fuse holder, grasp both ends (one side with each hand). Push inwards (spring) and rotate your right hand counterclockwise. After that half turns (while the other does not), release the inward pressure and pull the two halves apart. Do the reverse to close it back.

[fintstone]

You can check your fuses with the light or meter. The top side of each is supply (hot) and the bottom is the end going to the circuit it protects. With the light, you attach the ground wire to ground and probe the top of each fuse. If unswitched (battery is hooked up and voltage is present), it should light. If not, then it may need switched power of some sort (depends on which fuse). Anytime you get the top hot (12v) by simply having the battery attached for some, switching on the key for others or pulling a knob for others, the light should come on when probing the top end and if the fuse is good, the light should also come on when you probe the bottom (when there is power at the top).

If you disconnect the battery, you can test each fuse in the circuit with your meter set on ohms. Aftre making sure power is off, simply put one probe on the top and one on the bottom. Each should read a short (and beep if you have that meter function).

[megerian]

Excellent - thanks for the clear explanations

[megerian]

Well, unfortunately, the fuse in the white holder is fine, and the position 3 blue fuse is also fine, and yet the cab top won't move. It was working fine a couple of weeks when I last used it, and now it doesn't move. Any ideas?

[pavegeno]

There is a cabriolet control module under the dash. I had the same issues with my 88. Chased limit switches, fuses, and parking brake switch. Finally replaced the control module and it has worked perfectly since 2012.

https://www.ecudoctors.com/collections/porsche-911-3-2-carrera-1984-1989/products/porsche-911-convertible-top-control-br-unit-911-618-313-00-exchange-new-design

[fintstone]

Sorry. I don't have the wiring diagram that includes the top...so I really cannot help. Maybe start with unplugging the module and then then plugging it back in.

[porschedude996]

That fuse holder doesn’t look like an OEM Holder.

[Bill Douglas]

Handy helpful hints...

Put an old towel or similar under the panel so when you drop a fuse you don't lose it forever.

Every so often, maybe once a year, remove a fuse and scrub the contacts on the fuse and fuse holder with a scotchbrite. Put the fuse back and spin it around a few times. The metal oxidises slightly.

[famoroso]

I converted my former 1988 M491 cabriolet to manual operation as soon as I was able to amass the parts.

At 10 times in, you might consider doing the same. Unless you REALLY like troubleshooting the Rube Goldberg contraption that is the power top mechanism on these cars. Amazing engineering back in the day, but I held my breath every time I operated mine.

Sorry, I'm not more helpful in this case, but if I still owned a 3.2 cabrio with power top, I woulda bought this (perhaps it's still available?) the day it was listed...

https://forums.pelicanparts.com/porsche-911-used-parts-sale-wanted/1124054-fs-convertible-top-control-nos-91161831100-a.html

Good luck.

[sugarwood]

Some basics covered in here

Getting to know our 911's: Performing some basic tests before there is a problem

[megerian]

I seem to recall the module was under the passenger floorboard and not the dash?

[86 911 Targa]

^^^^^
Here is the factory CKT for your car.

Best,

Gerry

[Nick Triesch]

While you are checking, replace all your plastic fuses with ceramic ones. They sure helped me.

[GH85Carrera]

Originally Posted by porschedude996

That fuse holder doesn’t look like an OEM Holder.

Actually it is.

It fusses the trunk light, and the interior lights as well as the clock. At least on my 85 Carrera. It is real easy and handy to pop open the fuse holder if you are working in the trunk, or have the doors open and want no power to the dome lights or clock.

I use it mostly for working in the trunk area. Reconnect, and reset the clock and done. I have to GUESS that the factory did it for the mechanics to work in the trunk area and not run the battery down.

[megerian]

Well - keeping in mind the adage about ruling the out the easy stuff before throwing money at a problem - i was close to pulling the trigger on a new cabrio control module, but I just decided to go through all the fuses again, and just check everything, and I also stumbled across an old pelican forum post to just stamp the passenger footwell where the module is located, and ....

it's working again! Crazy but true.