Lorenfb

It appears Porsche had/has a design problem, or their thinking was to have the
bulb light when the key if off. A simple solution is to cut the circuit track to the
power side (#30) of the bulb & jumper to the #15 power which connects to the
other bulbs.

JasonAndreas

Yes and I posted pictures of it last summer, the cabriolet mod was also mentioned HERE

The exact instructions from Porsche are:

• Remove the time clock.
• Break the connection from lamp socket #2 (Arrow "A")
• Remove the insulating coating on the current track at arrow "B"
• Using a short length of wire, connect point "C" of resistor to point "B". Solder connections using a low wattage, small tip soldering pencil. Be certain no other conenctions are made or bridged.
• Reinstall time clock.

jjbunn

What would be really helpful is to see the relevant section of the electrical wiring diagram/schematic. I'm still confused about why the bulb is there, and what the implications are of removing it for a non-cab 964.

Lorenfb

"I'm still confused about why the bulb is there, and what the implications are of removing it for a non-cab 964."

The bulb provides an indication of a cab top ECU fault.

1. The bulb should NOT be removed on a cab top vehicle;
a. no cab top fault indication
b. A central informer general fault may occur.

2. The bulb should NOT be removed on all other vehicles;
a. A central informer general fault may occur.

Bottom Line: If a reduction in standby current is desired, then the mod outlined
before should be done, i.e. use #15 power to power the bulb & not #30 power.
This should be about a 5 minute effort.

Pesty

Well bill. Thanks for the info.

Ever since I had power problems last year Ive been wary of any power drains so I will take my clock out and check to see if lamp 2 is there or not. turned out to be duff battery but even so every little helps.

Thanks for bringing this to our attention.

Pesty

well that was quick. lamp number 2 removed. time taken 5 seconds.

Im getting a crack hand at this 964 lark.

next stop taking engine out

Bill Gregory

Glad I said it might be old news

Bill Gregory

Porsche thinks it OK, putting the modification into production in 1994, and recommends it for 89-93 964's. I'd think if it caused a central informer fault, that Porsche would have recommended a different course of action. In my case, I have no indication, beyond a reduction of approx 10ma of draw, that anything was done.

Is this caution based on first hand experience?

Lorenfb

"2. The bulb should NOT be removed on all other vehicles;
a. A central informer general fault may occur."

The signal from the cab top bulb was brought into the central informer for a reason!

Bill Gregory

Right....10ma It was really a plot by Porsche to sell more batteries, but when they figured out in 1994 it wasn't working, they issued the service bulletin.

Lorenfb

"Right....10ma It was really a plot by Porsche to sell more batteries, but when they figured out in 1994 it wasn't working,"

Sounds like a post from the "other" forum and hardly expected from a "super moderator".
It really doesn't provide insights to the issue, does it?

Again:

The central informer was connected to the bulb to sense the fault state of the cab top ECU.
The voltage at the bulb appears to provides info to the central informer:
1. "hi" - 12 volts (bulb not on), no cab top fault
2. "lo" - ground (bulb on), cab top fault.

If the bulb is removed, does the central informer "see" a "hi" indicating a "no fault"?
That's the issue which the thread hasn't answered.

Bill Gregory

My apologies if the icons didn't bring the intended sense of humor to the reply. Nothing personal was intended.

Sorry, but we'll have to agree to disagree on this one...Porsche issued a service bulletin which is very clear. Would you like me to email it to you?

JasonAndreas

In a coupe it will not register a fault and in a cabriolet you don't remove the bulb...

Lorenfb

"In a coupe it will not register a fault and in a cabriolet you don't remove the bulb..."

Thanks Jason for clarifying the issue.

"My apologies if the icons didn't bring the intended sense of humor to the reply. "

I guess I've spent too much time in the PAST on the "other" forum
to appreciate real humor when it occurs versus attacks. Sorry for the
mis-interpretation.