Rewiring radio power feed

Boxwolf · Post by **Boxwolf** » Tue Apr 07, 2009 9:43 pm

I have a nice, but power hungry radio that continues to consume power while switched off. The car has started giving me a low battery warning and I'm concerned the battery will go flat overnight. Is there any way to (easily) cut power to the radio when the ignition is switched off?

Vanny · Post by **Vanny** » Tue Apr 07, 2009 9:52 pm

Well you could rip the radio out and get a better one, it really shouldn't need that much juice when its not in use, only a tiny weeny bit of juice to remember radio stations etc

If thats not a suitable option (and it probably isnt) then try pulling out the fuse for the cigarette lighter, i'm pretty sure thats the same feed for the radio (i could be wrong) and that way it will be isolated.

My only real worry is that if your using the car semi frequently then the battery/alternator shouldn't be going flat, might need a check!

Boxwolf · Post by **Boxwolf** » Tue Apr 07, 2009 10:44 pm

I was thinking of a more permanent solution really, such as changing the power source to the radio so it is cut when the key is off.

I think it was paranoia thinking the battery light came on while the engine was running I was very tired when I put the car away (and still am) but the little window on the battery has been black since i checked earlier today. These have been known to lie apparently but I will check the voltage tomorrow with a multimeter. If I can identify the radio fuse (anybody know the fuse number?) i'll check the current accross it while the radio is off.

Just to be safe, (read paranoid) I left the car outside facing away from the garage so if it does go flat i'll be able to get someone to jumpstart it.

If all else fails i'll just have to pull the radio out and find one that is OFF when its off.

Vanny · Post by **Vanny** » Wed Apr 08, 2009 5:38 am

well just wire it into an ignition switched source. Likely hood is that if you trace the white and red bundle of wires by the clutch pedal, then at the big (brown or white) multiplug you'll find a short green wire with a red connector on it, thats ignition switched live, and conveniently right next to where you want it.

Still, i would be more concerned about a proper fault over a radio, its not common for them to knacker batteries all that quick (unless they are super cheap or super old).

Jaba · Post by **Jaba** » Wed Apr 08, 2009 8:25 am

I dont think its the radio that is the problem.
A radio that is switched off does not consume a significant amount of power. It would take months to drain a fully charged good condition battery.
Even one switched on at full volume would take a long time to flatten a 40 ah battery. Unless of course you are running a mobile disco rig.

I would check your battery and alternator first.

Boxwolf · Post by **Boxwolf** » Wed Apr 08, 2009 9:29 am

Checking battery and alternator voltage this morning, is there any way to test the health of a battery?

Boxwolf · Post by **Boxwolf** » Wed Apr 08, 2009 10:11 am

Okay, I checked the battery while connected with everything switched off and it measured about 12.2 volts (50% charge according to wikipedia). Should I disconnect the battery before measuring it?

I measureed the voltage between the contacts with the engine running and it was over 13v so no problems with the alternator.

I then disconnected the negative terminal and tested the current between the lead and terminal with everything switched off and it had a current of 2.1 measured with 200ma setting on multimeter. I'm guessing this is 2.1ma? not sure if thats bad or not. As i reconnected the terminal it sparked a little.

The car is still starting fine so I suspect the hydrometer may be lying?

Way2go · Post by **Way2go** » Wed Apr 08, 2009 12:44 pm

Boxwolf wrote:
I measureed the voltage between the contacts with the engine running and it was over 13v so no problems with the alternator

Not necessarily, try this with the engine running and a load too such as headlights, rear screen heater etc. Also seems low, would expect 13.5 to 14ish.

2.1 mA should be no problem to a normal healthy battery unless the car is to be unused for a long period and then best disconnect it. Otherwise the 2.1 mA will eventually take the battery into deep discharge from which you are unlikely to be able to ever recharge it again.

Boxwolf · Post by **Boxwolf** » Wed Apr 08, 2009 3:09 pm

It was about 13.5, but I can check with the headlights on. What should the figure be with a load such as this?

I'll need to identify the radio fuse in case I need to leave the car for a while. How long would it take for the 2.1ma to drain the battery if left?

Can anyone tell me what fuse number the radio is?

Vanny, you mention a green wire with a red connector near the clutch pedal. Which wire would i need to cut and connect to this to put the radio on ignition switch?

Way2go · Post by **Way2go** » Wed Apr 08, 2009 4:25 pm

Boxwolf wrote:It was about 13.5, but I can check with the headlights on. What should the figure be with a load such as this?

Should still be no lower than 13.5V. With a normal complement of energy consuming things, you should still be maintaining a charge to the battery when it needs it.

Boxwolf wrote: I'll need to identify the radio fuse in case I need to leave the car for a while. How long would it take for the 2.1ma to drain the battery if left?

This won't be a problem on a good battery for some time. But I've had a battery go into deep discharge when the car was left for a month without use and that battery had worked ok on the car until then.
If the car is in regular use, don't worry about it. If it's not going to be used for a while, just disconnect the battery.
If you switch(/de-fuse) the memory feed to the radio each time, you're making it unnecessaily painful for yourself, will have to enter the code each time you want to use it and reacquire all your stations.

Post by **Tim Leech** » Wed Apr 08, 2009 4:35 pm

Maye a stupid answer but if the radio is a "front off" type, just take it off, the CD Radio in my TRS is live all the time so I just unclip it.

Way2go · Post by **Way2go** » Wed Apr 08, 2009 4:38 pm

Roverman wrote:Maye a stupid answer but if the radio is a "front off" type, just take it off, the CD Radio in my TRS is live all the time so I just unclip it.

That doesn't eliminate 'standby' power though does it. The radio is still ready to go with it's memory intact when you put the front back on!

Jaba · Post by **Jaba** » Wed Apr 08, 2009 8:02 pm

Going back to your original post - your one symptom is the no charge to battery light came on once.
This is nothing to do with your radio draining the battery as you have measured only 2.1ma. This is no drain at all effectively.

The most common cause of the warning light is a not turning, faulty or failing alternator not the battery. There can be wiring and earthing issues too so check the alternator connections carefully for damaged wiring or corrosion.
A replacement alternator is the next logical step. But not realistically
after just one flicker of a warning lamp.

Boxwolf · Post by **Boxwolf** » Wed Apr 08, 2009 9:05 pm

Jaba wrote:Going back to your original post - your one symptom is the no charge to battery light came on once.

Actually the symptom was the battery's hydrometer showing up black. I dont think the warning light did come on I was very tired at the time and had just finished squashing my poor BX into a garage that was far too small for it because my parents insist it obstructs the neighbours if I leave it outside.

Jaba wrote: The most common cause of the warning light is a not turning, faulty or failing alternator not the battery. There can be wiring and earthing issues too so check the alternator connections carefully for damaged wiring or corrosion.
A replacement alternator is the next logical step. But not realistically
after just one flicker of a warning lamp.

After checking the alternator output I think its okay, but I will check it tomorrow with a load on it such as the headlights.

I'm also concerned the drain reading I took was false, as i'm no good at converting figures from a multimeter. The multimeter was set to 200ma, and it showed 2.1, but would it have shown 21 if I had set it to 20ma? I also noticed I had the multimeter + lead in the 10A socket which may have disrupted the low ampage reading. I'll test it again tomorrow.

Boxwolf · Post by **Boxwolf** » Wed Apr 08, 2009 10:40 pm

Incidentally, I found this on a very similar model of radio to what I have http://www.fiatforum.com/i-c-e/89379-si ... model.html which does imply I should be concerned.