Hoserpilot

Bought a beautiful 993 last month. Fm radio reception was poor so I decided to check the antenna. I have a k40 detector installed. K40 was spliced into the harness. As I pulled the radio out some old electrical tape was loose which exposed some wires. Bare wire contacted some metal which sparked causing the #38 fuse to blow.

Prior to this event everything worked normal except the poor fm reception. After replacing the fuse the radio works again. Fm reception still poor.

A couple new problems occurred. K40 will power up only in the accessory position. When I start the engine the k40 turns off. It will not work with the engine running. Also the radio always has power. When I turn the car off and open the door the cdr210 is still playing some sweet Van Halen. I have to press the radio power button to turn it off.

I went to a radio install place to install an iPod adaptor. The tech tried to find the problem. He accessed Porsche wiring documents from multiple aftermarket installers. After using a multimeter to confirm the weird power issues at both the radio harness and just aft of the ignition he decided the wiring problem was above his expertise. Heck, it confused me too! Even my neighbor who builds level D (airline) full motion flight simulators can't figure it out.

The tech and his support folks thought maybe something happened when the bare wires touched. The fuse obviously popped but they surmise that something happened in the ignition since that is where the wiring all meets. He was more technical but it's 2am and I'm not an electrical guru. Any ideas? I've read through pages and pages of posts which somewhat backup their claim.

Just joined and sent my Paypal payment.

Thanks for all your help.

ToreB

It's diffucult to comment on the power supply problem without being able to do measurements.
The radio is supposed to have both a permanent +12V power feed (Terminal 30, red wire) as well as a separate switched +12V feed from the ignition switch through fuse 38. ("R" (radio): red/black wire)
If the radio does not turn on/off as expected when turning the ignition switch there might be a problem in the switch itself, not providing the switched +12V to the radio. This could be checked with a voltmeter connected to the red/black wire. This wire is supposed to carry +12V in all three on-positions on the ignition switch. (pos 1, 2 and 3)

Regarding reception issue: Be sure that the antenna amplifier power supply lead is connected to a +12V output on the radio. (the 993 schematics mention this output as pin 5,"Antenna") This thin (often white) is bundled with the antenna coax cable. Modern head units have a blue lead called "Remote" or something that provide +12V when the head unit is on.
Hope this helps.
Cheers,
Tore

M. Schneider

What ToreB said ^^^

Hoserpilot

ToreB,

Thanks for the reply.

Everything worked normal prior to pulling the radio out. The bare wires touched the stereo mount and sparked. Little puff of smoke and fuse 38 popped. No big deal right? Tape up the bare wire. Replace the fuse. Listen to music. Drive around with the K40 chirping when it gets a radar return...

But!!!

With the key in the ignition just prior to start. All warning lights and bells are normal and the red and black is properly showing 12 volts. As soon as I actually turn the key to the start position the red and black drops to zero volts. I tested this at the radio and just after the ignition switch as well.

What am I missing? There is only one fuse right? Number 38 (I know about the 7.5amp on the radio too)

Where is the next place to look? Could the electrical spike zap something in the ignition causing it to act this way? Did I weld something together? hahaha. Did the ignition switch act as a "fuse" and fry?

I've gone through some posts regarding the ignition switch. My understanding is there are two parts. First is the physical cylinder that the key turns. Second is the electrical portion that can somewhat easily be replaced....if I'm flexible and maybe take the drivers seat out.

What other tests can I do to isolate the problem?

Measurements of red/black wire---
Key in - 0 volts
first click to the right - 0 volts
second click to the right - 12 volts
turn key to on position, car starts - 0 volts

Radio can be turned on and off at any time, with the key in my pocket. This did not happen prior.

K40 detector only works when the key is in the second position and red/black showing 12 volts. Once the car is started and the red/black drop back to zero volts the radar detector loses power. This did not happen prior.

ugh....

ToreB

I would think there's something wrong with your ignition switch. But I would think it would stand up to a short as you describe, so I can't explain why it's acting up.
As far as I understand the schematic it should produce +12V in all three on positions, here's a schematic cutout:

Cheers,
Tore

techman1

Is it possible to pull out the radio unit again? My thought is a wire may have been spliced onto the bare wires you shorted out. It slipped off when you pulled the unit out.

When the radio is out, get a lot of light into the radio hole, even from below. Look carefully for a bare/disconnected wire.

My guess is the switched wire from the ignition became disconnected, and it was used to switch your K40 and radio on/off

Hoserpilot

This afternoon I removed the radar and laser jammer wiring that was spliced into the radio wiring harness. Got a better look at it and was able to do multiple tests of the wiring with the multimeter. The tests confirmed that the ignition switch is the likely problem. Got one ordered. Thanks again for the wiring diagram and the help.

Digging under the dash I found the old wiring for the original audiovox cell phone. After a quick google search I had to laugh at how big cell phones used to be!!!

For now the radar detector and jammer are plugged into the hot 12v power feed until I replace the ignition. I kinda like being able to turn the radio on/off without the key. Lol. Just have to remember to turn them all off!