'87 3.2 with mysterious radio problem

brick · 09-27-2005, 05:34 PM

I've had a 100,00mile 1987 3.2 coupe for a six months. It checked out fine by the porsche dealership before I bought it. After a few months, I noticed that the fasten seat belt light would come on periodically while driving but didn't think much about it. During the past two months, the previously installed XM radio would power off for a few seconds frequently throughout the day and then come back on. I thougt this was probably a faulty XM wiring situation. I had a new blaupunkt radio put in that had an accessory jack and had the XM radio hardwired. Now the XM radio works perfectly but the new blaupunkt radio mysteriously powers off for a few seconds to a minute and then comes back on, just like the old XM radio. The fasten seat belt light still comes on periodically while driving. I let the radio installlation shop look again and they put the ground wire of the radio and the XM together. No help.

Paying closer attention while driving, I have noticed that about half of the time when the radio goes out, the fasten seat belt light just came on. Typically it is worse later in the day after driving a while. When the radio does go out, I am typically driving over 2000rpm later in the day When I take it out of gear and drift back down to 1000rpm, the radio will come back on. Without turning on the engine, I can have both the radio and XM on and they work fine. No fasten seat belt light comes up either. I can turn off the XM radio and the blaupunkt radio will only occasionally power off. I have tested the battery with a digital multimeter while parked at 2000rpm with everything turned on but it still reads no more than 13.8v. I have had no other electrical gremlins such as flickering lights, etc..

I think it is the voltage regulator even though battery voltage testig was normal . Any suggestions?

fuelie600 · 09-28-2005, 05:05 AM

Sounds like a bad connection or a loose ground somewhere. From the Bentley schematics, both the radio and the seat belt control unit have a connection to the ignition switch. The seat belt wire is red/blk and the radio wire is grn. You might start there.

I doubt it's the voltage regulator. When mine went, it would intermittenly charge to 18.5 volts!

Good luck!

frenchy 911 · 09-28-2005, 06:38 AM

I have the same issue with my seat belt sign which go on and off

As far as my radio, I cannot turn it off while engine is on very weird. Even if I turn the knob to the off position the radio display stay on.

Does nay one has an idea about how to fix these couple of issues?

fuelie600 · 09-28-2005, 09:36 AM

Maybe your ignition switch is starting to fail? That's the only thing the two items have in common.

brick · 10-06-2005, 04:24 AM

I still had a feeling it was the voltage regulator. My problem was how to test the battery while I was moving as this was the only time it occured. I couldn't talk my wife to sit in the trunk with the voltimeter attached to the battery while I drove around. So I bought a 12V cigarette plug adapter from Radioshack and hooked up the voltimeter to it. After driving it around for awhile, lo and behold, the volts spiked to 18. I also noted a slight increase in the A/C fan as well.

tubwreck · 10-06-2005, 05:05 AM

I had a similar problem in an '87 -- it turned out to be the seatbelt warning control unit.

frenchy 911 · 10-06-2005, 05:14 AM

Ed,

how did you fix It, change the control unit??

ken_xman · 10-06-2005, 05:34 AM

I have the same problem on the 87 as well. Never looked into it.