Radio shut off, seat belt light on, Erratic Voltage

[zugvogel]

I thought I'd share what my '85 911 gave me as a homework assignment over the last few weeks.
Let's start at the beginning, a couple of months ago:
occasionally when accelerating and revving the engine above 3000 my seat belt light came on and most of the time the radio shut off, the internal safety mechanism kicking in to protect the circuits.

My first assumption was, that the aftermarket radio has probably not been installed properly by the PO and an occasional short causing the problem. So climbing under the dashboard, taking out the radio and checking all cables and connections, I discovered nothing uncommon on the radio wiring, but the light bulb for the heater fan was actually shattered and certainly a potential for a short as I found out while moving the cables around. So a new light bulb went in and I was certain the problem was solved.

Well it was not, as it continued flashing me with the seatbelt light and shutting off the tunes. So back to the drawing board, thinking hard, but honestly I was clueless for a few weeks, especially since I was not able to establish a pattern on when it was failing, it only happened occasionally.

So things turned around when I installed my radar detector, which I had programmed a long time ago to display the onboard voltage when no alarm goes off. I kinda like that when I use it on my motorcycle... anyhow, the next time the seat belt light went on and the radio off, I was able to see what happened voltage-wise. Sure enough the voltage went beyond 14V, into the high 15's and beyond - that's when the Beltronics switches from displaying the actual voltage to "HIGH VOLTAGE" combined with a frantic beeping. So now I was able to see the voltage rise and drop, basically all good below 2500 revs and then going nuts as soon as I went beyond 2500. But after a 10 minutes or so of driving everything went back to normal..... mmhhhh.... strange.....

Having had not much experience with electrics up that point and still believing it is voodoo, I thought about it for another few weeks and with my radar detector/voltage meter I was able to establish a pattern:
The voltage only went nuts, after I had parked the car with a hot engine, left it off for a few minutes, half hour, then started to drive again.
To me that meant that a component was overheating close to the engine while the airflow was interrupted but the engine still being hot. I did know that a car has a voltage regulator and I was beginning to see the dust settle and the solution to my problem started to take shape. So I dove head first into this and other forums to do my research and sure enough it all sounded plausible, especially after seeing where the VR is located: right in the cooling airflow when the engine is running, and right in the heat rising up from the engine when it is not running.
So Pelican to the rescue, I ordered the last VR in stock, mounted it as soon as it was delivered today, and...... success!

No more erratic voltage increase, no more restricted radio listening, and certainly no risk anymore to fry the battery, the computer, and what ever else.

As for the actual procedure to replace it, it was really (almost) a breeze: disconnecting the battery, taking the fan belt off, I moved the fan housing forward enough to be able to pull the VR off. I did not disconnect the alternator wires - you don't have to take the alternator off the car to change the VR. This is good, because taking it out seems to be a tight fit - don't fix it if it ain't broke is my motto - especially on cars. The only glitch I ran into was that the Valeo VR I bought was just a tiny bit too big. The air duct behind the alternator did not seat properly so I had to file the VR (plastic) down a bit until the duct easily went back on.


I hope this little tale helps anyone with a similar experience. Luckily I caught it early enough - the battery did not boil over and everything electrical still works fine.


Happy motoring!

[S15508g]

Originally Posted by zugvogel

I thought I'd share what my '85 911 gave me as a homework assignment over the last few weeks.
Let's start at the beginning, a couple of months ago:
occasionally when accelerating and revving the engine above 3000 my seat belt light came on and most of the time the radio shut off, the internal safety mechanism kicking in to protect the circuits.

My first assumption was, that the aftermarket radio has probably not been installed properly by the PO and an occasional short causing the problem. So climbing under the dashboard, taking out the radio and checking all cables and connections, I discovered nothing uncommon on the radio wiring, but the light bulb for the heater fan was actually shattered and certainly a potential for a short as I found out while moving the cables around. So a new light bulb went in and I was certain the problem was solved.

Well it was not, as it continued flashing me with the seatbelt light and shutting off the tunes. So back to the drawing board, thinking hard, but honestly I was clueless for a few weeks, especially since I was not able to establish a pattern on when it was failing, it only happened occasionally.

So things turned around when I installed my radar detector, which I had programmed a long time ago to display the onboard voltage when no alarm goes off. I kinda like that when I use it on my motorcycle... anyhow, the next time the seat belt light went on and the radio off, I was able to see what happened voltage-wise. Sure enough the voltage went beyond 14V, into the high 15's and beyond - that's when the Beltronics switches from displaying the actual voltage to "HIGH VOLTAGE" combined with a frantic beeping. So now I was able to see the voltage rise and drop, basically all good below 2500 revs and then going nuts as soon as I went beyond 2500. But after a 10 minutes or so of driving everything went back to normal..... mmhhhh.... strange.....

Having had not much experience with electrics up that point and still believing it is voodoo, I thought about it for another few weeks and with my radar detector/voltage meter I was able to establish a pattern:
The voltage only went nuts, after I had parked the car with a hot engine, left it off for a few minutes, half hour, then started to drive again.
To me that meant that a component was overheating close to the engine while the airflow was interrupted but the engine still being hot. I did know that a car has a voltage regulator and I was beginning to see the dust settle and the solution to my problem started to take shape. So I dove head first into this and other forums to do my research and sure enough it all sounded plausible, especially after seeing where the VR is located: right in the cooling airflow when the engine is running, and right in the heat rising up from the engine when it is not running.
So Pelican to the rescue, I ordered the last VR in stock, mounted it as soon as it was delivered today, and...... success!

No more erratic voltage increase, no more restricted radio listening, and certainly no risk anymore to fry the battery, the computer, and what ever else.

As for the actual procedure to replace it, it was really (almost) a breeze: disconnecting the battery, taking the fan belt off, I moved the fan housing forward enough to be able to pull the VR off. I did not disconnect the alternator wires - you don't have to take the alternator off the car to change the VR. This is good, because taking it out seems to be a tight fit - don't fix it if it ain't broke is my motto - especially on cars. The only glitch I ran into was that the Valeo VR I bought was just a tiny bit too big. The air duct behind the alternator did not seat properly so I had to file the VR (plastic) down a bit until the duct easily went back on.


I hope this little tale helps anyone with a similar experience. Luckily I caught it early enough - the battery did not boil over and everything electrical still works fine.


Happy motoring!

After 11 years and finally someone will say thanks. Ordering my vr, probably a bit more expensive then back in 09. Lol.

[darrin]

ss15508g - Unfortunately the internal VR failure also generally means that the alternator itself is also in need of a rebuild. Suggest you find a local alternator shop (old school kinda place) and have your alternator inspected/rebuilt while it's out.

[john walker's workshop]

New regulator brushes on an old worn commutator don't last long, or may not contact well. Ya need the whole thing rebuilt or get a new Valeo.