Car Radio turning On and Off only when engine running (Bad grounding?)

Thread Starter

francisconqn

Joined Apr 23, 2020
5
Hi, i have recently installed a aftermarket radio with built in display, the problem is that when the engine is running, the radio turns off for 5 seconds and turns on for 5 seconds, and this cycle repeats indefitly. What do you think? probably a bad grounding? should i perfom voltage drop tests?
 

MisterBill2

Joined Jan 23, 2018
18,179
The very first place to check is at the radio. An excessive voltage would be due to a failed alternator voltage regulator, not a failed alternator. OR, if this is in a motorcycle then possibly a bad connection to the big zener diode some use to stabilize the voltage.
A poor battery connection will result in an excessive charging voltage also, in some systems.
So now the TS has a lot of things to check.
 

Tonyr1084

Joined Sep 24, 2015
7,853
Check the battery voltage with the engine running (~14V).
I had a similar problem where the alternator was faulty and the battery voltage was 19V!
Had a 78 Ford Granada with a mechanical regulator mounted on the fender. One morning on the way into work I noticed that my headlights were doing a bang-up job of lighting the roadway ahead. Didn't take long to realize that one of the relays in the mechanical regulator was stuck. Rolled down the window and wrapped on the fender and all of a sudden all the lights dimmed back down to a more normal luminosity. Later that day I replaced the regulator.

Had an old car radio I built into a boom-box arrangement. The box had the radio, a battery and a 12V charger set to charge the battery to 13.8 volts when plugged in. The radio would play when not plugged in but would not work when I plugged it in at work. It worked perfectly at home, so why not at work? I found out that the output voltage at the work outlet was 123VAC whereas at home the outlet was pushing 115VAC. The charger was scrapped out of an old emergency light unit and slightly modified to continue to power the radio regardless of power or battery operation. Apparently the car radio I had was not happy with the higher voltage.

Just my personal experiences. But I would agree, check the voltages. In a normal charging scenario, when starting the car it is normal to see battery voltages go up as high as 14.7V (from personal experience). This typically happened on older batteries (not older models, old as in close to the end of life). I keep battery voltage indicators in both my vehicles and regularly watch the output voltage when I start the car and occasionally while driving. With strong (new) batteries, I might see 13.9V after starting with engine idling. After driving for five minutes or so battery voltage drops to 13.6V at an idle. While engine RPM's are up above idle I never see voltage above 13.8. My vehicles are a 2017 Tacoma and a 2009 Venza.

With a Walmart battery in the Venza I noticed after about a year that battery voltages were going as high as 14.7, but overnight resting battery voltages were down in 11.9 range. The battery began needing a jump to start and I began suspecting the alternator as being the issue. While driving I noticed voltages around 13.4. I thought I needed to replace the alternator. But the guy at Toyota said they put a new battery in (temporarily) and the charging system worked perfectly normal. So I took the one year old battery to Walmart and they replaced the battery on warranty. The current battery is in there some three to four years now and there has been no under voltage issues. Charging systems seem to be pretty robust as long as you don't try to jump start someone else with a weak or dead battery. Alternators are not designed to handle such high loads. The right way to jump start another vehicle is to connect the two vehicles together with jumpers. The donor car should be idling and should idle for about 10 minutes, charging the jumped car. Then - before trying to start the jumped car - turn the donor car OFF but don't disconnect the jumpers. The jumped car should start. Remove the jumpers and restart the donor car and you'll never hurt your alternator. I HAVE seen alternators damaged in the past by people jumping a car while the donor car was running. Helping a friend could get very expensive. Especially with today's high prices.
 

Thread Starter

francisconqn

Joined Apr 23, 2020
5
Check the battery voltage with the engine running (~14V).
I had a similar problem where the alternator was faulty and the battery voltage was 19V!
Some news here
i found that the 2 wires from the alternator were disconnected (it is a 3 wire, externally regulated one), it wasnt charging obioulsy, so the voltage with the engine off and idle is the same, 12.7v

Now i have to rewire the alternator so it can charge the battery (i read some books on car electronics, but there is a little information on externally regulated ones) and the radio is still turning on and off (i thought that the problem was the voltage regulator)
 

Tonyr1084

Joined Sep 24, 2015
7,853
At 12.7 volts the radio should just play. Since it has a peculiar habit of 5 seconds on - 5 seconds off - repeat; I'd say there may be issues with the radio itself.

Fully diagnose the problem before you start throwing parts at it.
 

Thread Starter

francisconqn

Joined Apr 23, 2020
5
At 12.7 volts the radio should just play. Since it has a peculiar habit of 5 seconds on - 5 seconds off - repeat; I'd say there may be issues with the radio itself.

Fully diagnose the problem before you start throwing parts at it.
Thank you, i´ll meausure the voltages at the radio itself
 

Tonyr1084

Joined Sep 24, 2015
7,853
Just wondering what is the source of the 12 volts? I have a neighbor who wanted to hook a 12 volt air pump on his car and connect it so he could adjust air shocks without having to get out of the car. He hooked it to a 12 volt com line, not a power line. In short - he damaged his cars computer. That was some time ago and I am sure I don't have all the details right, but I'm wondering if maybe you've connected this radio to the wrong 12 volt source. And this is just a wild guess, so don't take it for gospel.
 

MisterBill2

Joined Jan 23, 2018
18,179
Just wondering what is the source of the 12 volts? I have a neighbor who wanted to hook a 12 volt air pump on his car and connect it so he could adjust air shocks without having to get out of the car. He hooked it to a 12 volt com line, not a power line. In short - he damaged his cars computer. That was some time ago and I am sure I don't have all the details right, but I'm wondering if maybe you've connected this radio to the wrong 12 volt source. And this is just a wild guess, so don't take it for gospel.
Certaiinly without verifying the 12 volt feed that is a possible cause. Running an external wire from the battery should be simple enough, although just measuring the voltage could be simpler. And using the negative connection point at the radio will be the best way to check.
 

MaxHeadRoom

Joined Jul 18, 2013
28,619
Now i have to rewire the alternator so it can charge the battery (i read some books on car electronics, but there is a little information on externally regulated ones) and the radio is still turning on and off (i thought that the problem was the voltage regulator)
Early electronic alternator regulators were simple comparator style that switched on/off at different intervals, depending on the generated voltage in order to maintain the correct charging voltage, , this caused a lot of grief due to interference noise.
Modern ones are now fixed frequency PWM. and cured the interference issue.
Is the after-market radio a reputable version? or a cheap import?
A modern auto, maintains a charging/system voltage of ~ 14.5v with the engine running.

'
 

MisterBill2

Joined Jan 23, 2018
18,179
What I have not seen is how the radio plays when the engine is not running. That is something that we should know. It might be that the radio is connected to a totally incorrect circuit. That cycle sounds more like a steering wheel heater circuit. The radio should connect to the accessory feed off the ignition switch. If the car is one of those with just a stupid start/stop button, then the radio should connect directly to the battery, with a suitably rated fuse. Consider that it might be the power feed switching on and off. It might be a current limited circuit thinking that the radio is an overload.
 

MisterBill2

Joined Jan 23, 2018
18,179
I see the title but I also see that no mention is made of when it is not running. AND that tells me that there is some information missing.
Alternator output will vary a fair amount between idle speed and faster driving speeds. And there are functions in a car that are duty cycle modulated. Heating cycles, mostly.
Besides that, power integrity is one of the first things to check when a device seems to go completely dead.. Also, it should be simple to check to see if the power stays on when the radio is off.
We never did get any statement as to just where the radio power connection was made. Some vehicles have two accessory power buses, (ACC1 and ACC2), in fact. If one of those is for heating then it might very well be switched off and on. And I really doubt that the radio is directly connected to the battery. That connection is for the memory power wire, and the clock power. Then there is the radio illumination connection, which may be dimmable like the other instrument illumination.
It might even be one of those radios with the anti-theft feature, that makes it not function correctly if it is not able to talk to the engine computer.
So once again, I suggest checking the power feed to verify that it is not switching off and on.
 
Last edited:

PaulEE

Joined Dec 23, 2011
474
I think what he meant is that the radio is flaky when engine is running, and it was inferred that otherwise (engine off), it works fine.

I have a sneaking suspicion that there are questions about this setup that we don't even know to ask, so I am waiting quietly in the inky shadows until the OP gives us some information...

I still want to know what the remote wire is connected to. If it is high impedance and it's picking up a full-bridge rectified 680 RPM idling engine, it may be turning the thing on and off. If then engine is off, no noise...a long shot, I do admit, but I thought it was a fun idea...:)
Paul
KI5VNH
 

Reloadron

Joined Jan 15, 2015
7,501
Hi, i have recently installed a aftermarket radio with built in display, the problem is that when the engine is running, the radio turns off for 5 seconds and turns on for 5 seconds,
Well while you don't say apparently the old radio worked fine. The new radio should have a pinout of what wires do what. Normally a ground wire and or chassis ground. Two power wires, one for constant power for clock, memory and other features. The next power is connected to the Accessory bus so radio only plays when ignition is set to ACCYs. Then comes stuff like speaker out all depending on radio make & Model. This is where it's nice to know make and model and wiring pinout?

Ron
 
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