1979 911SC weird - after driving for a while the radio power starts going on and off

FinallyGotOne · FinallyGotOne's Garage

what the heck, the radio over the last few weeks has started going off and on off and on... I looked in my manual and see no fuse for a radio at all. I am not sure what could make it do this. Think maybe the radio itself is just on the fritz?

schumicat · 06-30-2011, 08:22 AM

it could just be a loose crimp connector on the power wire if you have an aftermarket radio. most aftermarket radios will have an inline fuse on the wire as well. a failing voltage regulator could cause stuff to randomly turn on and off, but it would probably affect other stuff as well.

FinallyGotOne · FinallyGotOne's Garage

Ok, thnaks Schumi I'll get in there and check out the wires and connectors. Hopefully it's easily traced.

LJ851 · 06-30-2011, 08:48 AM

Hook a voltmeter up inside the car and monitor it while driving. There is a good possibility that your alternator is overcharging and tripping a breaker in your aftermarket radio. If this is the case you are also in danger of burning up other electrical components , possibly leaving you stranded.

Peter Zimmermann · 11:44 AM

If the problem is the alt/reg, you also might note a rotten egg smell in the car, and a battery boiled dry by an overcharge condition. This would be much more common with an updated alt/reg assembly (24mm nut on alt pulley shaft) than an original alt/reg (22mm nut on alt pulley shaft).

If you have a volt/ohm meter, connect the leads to the battery (black to -/red to +), bring the revs up to about 2500 and hold the engine at that speed for about 20 seconds. Any spikes over about 14.3 volts on the meter will indicate an alt/reg overcharge problem.

Flat6pac · 06-30-2011, 11:52 AM

Listen to the alternator/voltage regulator, been there in Columbus Ohio, coming from Delaware, going to PB Tweeks years ago and the battery was puffing. Really cooked. The radio was coming on and off for a few miles, then everything died.
Bruce

FinallyGotOne · FinallyGotOne's Garage

hmmm. uh oh. I went to start the car for lunch andthe battery seemed deadish. the starter turned really slowly, for a half sec, then the car started up. Also that red light on the lower portion of the Druck and Temp guage has been intermittently flashing red.

FinallyGotOne · FinallyGotOne's Garage

so i went to O'Relly's and they put their meter on my battery. According to their machine "not charging" is what came up. My battery was about 80% they said. Also, my radio was not doing anything weird, and my alt light was not on. But their hand held thing said "not Charging" not sure what to do now??
I do not have any meters myself.

911pcars · 06-30-2011, 05:01 PM

Quote:

Originally Posted by FinallyGotOne

so i went to O'Relly's and they put their meter on my battery. According to their machine "not charging" is what came up. My battery was about 80% they said. Also, my radio was not doing anything weird, and my alt light was not on. But their hand held thing said "not Charging" not sure what to do now??
I do not have any meters myself.

Get a second opinion.

Sherwood

SP2 · 07-01-2011, 06:43 AM

+1
Go to Sears Auto. They have good diagnostics.

moneymanager · 07-01-2011, 07:18 AM

I believe aliens have seized control of your car.

FinallyGotOne · FinallyGotOne's Garage

OK, so thinking NAPA was a pretty good shop i headed over there this afternoon to have them test my charging. He just put the thing on it and said your battery is at 90% go ahead and start it. I did, and after it idling for a few minutes he disconnected it and said your charging system is not working. he said it shows there is nothing charguing the battery at all.
so i have driven it about 45 miles since Thursday and the battery is still at 90%? seems if nothing was charging the battery I'd be at less than 90%. Doesn't starting it take a large percentage of the battery juice? I'd think all that starting would run me down. so if I'm at 90% I think something is keeping the thing charged. He said no, I have no electronic fuel injection on my 79 and all i'm running is the radio maybe. What about the fuel pump? what do you all think? I'll take it over to Sears when I get a chance next week, but in the meantime does what he said hold true or makle sense?

911pcars · 07-03-2011, 11:57 AM

A few things come to mind:

Radio cuts out. Is that the only symptom? If so, look at the radio circuit. As suggested, an intermittent source voltage wire connection could be the culprit.

Battery not charging? You would have other symptoms as well (including low cranking speed, dim headlights, misfiring, etc.) depending on the battery's state of charge. At one shop, the battery showed 80% charged, then 90% at another. Everything being equal, this could mean the charging system is working ok.

How about on-board indications the charging system is OK/Not OK? Is the charge light on the IP ON or OFF when engine is running? If it's ON, the alternator isn't charging. First confirm the bulb works with ignition ON, engine OFF.

Did the second shop actually disconnect the battery with the engine running? That procedure can damage the alternator.

You might be tempted to buy a new battery, but why if it isn't the issue?

Sherwood

FinallyGotOne · FinallyGotOne's Garage

OK, so going back to loose connection. At my positive side of the battery cable there is a connection where two thick red wires go in. see the pic. That bolt was loose quite a bit. After I discovered that I took it back up to O'Reilly and they put the black box on it again. Battery was about 100%. It was showing 12.5 ish for a while while it idled. I put on the lights and radio and it started coming down a bit then after a few minutes the engine noise changed a bit and we watched teh volts go up to about 13.8 then after a little while it dropped again. So it seems it is cycling on and off. He suggested my regulator was bad but I believe it's supposed to be cycling like it did, So I think all is well, and it was just that that connection was loose.
It was just at the muffler shop for the mirrored pipe work making my exhaust a 2 out. They must have loosened up the bolt to pull the pos+ cable off while they did the work to my car.
Now I still have the radio going off and on, so i am going to track this down when it cools down. Hot in Colorado today!

911pcars · 07-03-2011, 12:26 PM

Quote:

Originally Posted by FinallyGotOne

OK, so going back to loose connection. At my positive side of the battery cable there is a connection where two thick red wires go in. see the pic. That bolt was loose quite a bit. After I discovered that I took it back up to O'Reilly and they put the black box on it again. Battery was about 100%. It was showing 12.5 ish for a while while it idled. I put on the lights and radio and it started coming down a bit then after a few minutes the engine noise changed a bit and we watched teh volts go up to about 13.8 then after a little while it dropped again. So it seems it is cycling on and off. He suggested my regulator was bad but I believe it's supposed to be cycling like it did, So I think all is well, and it was just that that connection was loose.
It was just at the muffler shop for the mirrored pipe work making my exhaust a 2 out. They must have loosened up the bolt to pull the pos+ cable off while they did the work to my car.
Now I still have the radio going off and on, so i am going to track this down when it cools down. Hot in Colorado today!

The charging system doesn't normally cycle in that manner. Battery life will suffer in the long term if left in that condition. I'd take the tech's word for it and have the regulator further inspected.

What's happening with the charging light? I suspect it's going ON an OFF as well.

Purchase a multimeter (a HF cheapie will do). Connect to the source wire at any opportune access point to your radio, then observe the source voltage during normal operation. This should isolate whether it's the source voltage or the radio as well as monitor system voltage from the charging system.

Sherwood

FinallyGotOne · FinallyGotOne's Garage

No, the alt light goes off after startup and has been remaining off now.I read a post on pelican that the alternator only charges about 50% of the time. So cycling seems normal. But I'm no technician. The guy at o'reilly I would not take his advice, he was pretty clueless really. Thought my car was a 944!

teleski42 · 07-03-2011, 02:00 PM

Do you have an amplifier in the circuit?

FinallyGotOne · FinallyGotOne's Garage

No, no amp

911pcars · 07-03-2011, 02:22 PM

Quote:

Originally Posted by FinallyGotOne

No, the alt light goes off after startup and has been remaining off now.I read a post on pelican that the alternator only charges about 50% of the time. So cycling seems normal. But I'm no technician. The guy at o'reilly I would not take his advice, he was pretty clueless really. Thought my car was a 944!

Don't believe everything you read, especially on the internet, including this and previous responses.

Sherwood