Aussie Alan 993

What ever you prefer to call it, the light in the front bonnet of my 993 is not working.
Yes, I searched and only found some old threads with no solutions.
Of course, I checked the bulb and the holder, I also checked the wires have 12V until you put a bulb across them then it goes to 0V, I even put a LED festoon light and it glows very dim.
The engine lid light is good, so are the interior and glove box lights, the bonnet latch switch seems to work because the interior lights come on when you release the latch and the voltage on the wires goes from 12V to 0V when the latch is closed.
Is there some sort of module that controls this light, perhaps the one that controls the delay on the interior lights? Perhaps it is a bad ground, but where?
Thanks in advance for any ideas that help me nut this one out.

Cheers
Alan

hoggel

The 12v contact of the light should not go to 0V when the the bulb is in place, It should stay about 12V and the light should come on. You either have a bad ground that is not allowing enough current to illuminate the light or you have some high resistance between the fuse and the light that is limiting the current to the bulb.

[WRONG]Use a jumper from a 12V source (battery is right there) to one end of the bulb. Touch the other end of the bulb to the ground side bulb holder contact. Light? If yes, the problem is between the fuse and the 12V contact of the bulb holder. No light (and you know the bulb is good)? The problem is on the ground side. Pull the connector off the latch and jump the ground side pin to the opposite end of the light from the 12V. Light? If yes, the switch is not making good contact. No light? The problem is between the connector and ground.[/WRONG]

Aussie Alan 993

My best guess is a bad ground so I'll have to go looking. Any ideas where the most likely place to start?

AA993

hoggel

I'm sorry that I posted wrong information above.

[CORRECTION] The light in the luggage compartment is not controlled directly by the switch in the latch. The front latch switch is logic to the Alarm Control Unit. The alarm control unit turns on the "inside light" circuit by applying a ground to the luggage compartment light and the inside lights (in the 'automatic') position.

The ground for the switch on the luggage compartment lock is on the passenger wheel housing right.[/CORRECTION]

Aussie Alan 993

Thanks mate, that is very helpful, I will start there and hopefully get it sorted.
I'll post what I learn, hopefully get it sorted out.

BobbyT

Just a sidebar to this, but I found that if I leave the interior dome lights in the "automatic" position and lock the car with the remote (so the alarm is on), when I return two weeks later, the battery is stone dead. Apparently these settings creates a blind current draw...

nine9six

BobbyT,
Any chance your battery has seen better days? Curious as to how long its been in service?
Also, I wonder if you'd get the same results if you installed LED's in your cabin lights recepticles?

BobbyT

The battery is an East Penn 648MF, about a year old, so I'm confident it isn't a bad battery. The LEDs in the cabin lights might perform differently. For now, I just keep the dome lights in the off position, and turn them on as needed.

Aussie Alan 993

Hi Fellas,
I didn't have a lot of time after work today but I now know the problem is NOT on the ground side.
I took the light out and tested it on a 12V house alarm battery - its good, so no problem with the globe or the holder.
I then took a wire from the negative post on the battery and connected it to the ground terminal on the holder and no light. I then did the same from the positive post and connected it to the positive terminal using its normal ground wire and we have light, so the problem is with the positive side and not the ground side of the circuit.
Next I'll need to start studying the wiring diagrams to find where the 12V is coming from.
I'll keep going, but not tonight.

Cheers
Alan

hoggel

I just made this sketch for another thread. Fuse 11 also powers the glove box light, engine compartment light, buzzer, ... .

wes911 Mill

After reading the helpful posts and testing voltage and ground with my meter I did confirm it was the micro-switch. The micro-switch wires are not visible when looking down at the latch so they must enter into the luggage compartment behind the felt panels. So facing the latch and front of the vehicle i stuck my right hand index finger into the latch and touched & forced the micro-switch located on the right-side of the latch assembly and the light illuminated. So before you tear it all apart and replace the switch try this. And don't slam or drop the hood to shut it. Carefully lower the hood on to the latch where you will hear a click, then with the plams of both hands on both sides of the emblem gently push down until you hear the hood completely latch. Then use a polishing cloth to wipe your palm prints off the hood. And be glad you own a fine piece of Temperamental German engineering.

Railmaster.

Watch the old 993 Porsche promo films on Youtube, there they advice You to press gently on the emblem when You close the hood!

pp000830

This is not normal. When you lock the doors do both dome lights extinguish immediately? If they slowly go dark or remain illuminated your electrical system is not going into the sleep like mode. If things are working properly several draw items are shut down.

Could your problem be a sticking relay or an aftermarket item such as a audio poweramp tapped into an inappropriate hot wire?

oldman40

ok i will pile on this revived thread...

i haven't purchased a volt-ohm meter yet but for the engineering gurus in the rl crowd perhaps you can put me in the right direction or have dealt with this problem:

interior lights do not come on at all with door opening. but when i switch the light to 'always on' it works (both sides work this way). the door switches both trigger the annoying door open alarm when, yes, the door is opened, suggesting that the microswitches and door switches are working.

glove box light doesn't work, but the cig lighter and coin tray lights both work normally.

engine hood light not working.

frunk light not working.

all bulbs appear perfectly intact. battery well charged, no issues. no other electrical gremlins. no battery drains or dead battery issues even after weeks of non-usage.

so yes i know i need to check contacts with voltimeter, but any a priori ideas about what might be going on?

thanks!

oldman40

Update for any merciful e. engineers out there:

Glove box light fixed with loose connection. Multimeter shows very weak voltage at the hood light housing, 0.7 with resistance of 23ohms. Hood micro switch working, but not sure how to test current, it seems like a closed system, no exposed contacts.

Any thoughts on where the resistance is coming from?