Stereo ignition wire voltage

[gba88]

Anyone have an idea of why my ignition wire in the stereo harness is 10.7v with the ignition off? This is the violet/white wire.

Also, the Light blue/red wire (illumination wire I think..) has the same behavior.... about 10.xxV with ignition off and then they both go up to 12.xxV when the ignition is turned on. I've never worked on a car before where the radio ignition wire had voltage in it until the ignition was switched on.

This is a 96 btw. I really don't think this is "normal", so I'm open to any troubleshooting suggestions. Thanks!

[jocko463]

Most modern radios require some sort of constant voltage to maintain things like the clock and any preprogrammed settings (station selections, EQ settings, antitheft devices, etc)....the radio has a memory much like a computer and needs a constant power source to keep it alive. So having a lead or two running to the radio carrying power even with the ignition off is not abnormal. As far as your situation, it sounds to me like you are reading near battery voltage on these leads....which you should... and if your reading is just a hair under 11v, then maybe your battery is on the way out....or you could have some high resistance (voltage drop) due to some chassis grounds that may be less than ideal. The reason it changes to 12v after the engine is running is due to the alternator and charging system providing something greater than 12v to charge the battery.

Mike
00XJ

[lawsoncl]

There may be a diode inside the radio between the ignition and the always-on wire. Or pair of diodes in series, looking at the voltage drop. This lets the ignition feed the other parts of the radio such as the memory and lights without having to hook those up?

[gba88]

Thanks for the reply. The 12v readings are not with the alternator running... just with the key switched into the accessory position. I'm aware of the constant hot lead that is required to keep the settings, but as far as I can see, this is accomplished already by the pink wire in the stock connector (yellow wire in most radios).

Also, the pink wire with ignition off is reading the full 12.xxV, so it's definitely not a battery issue as far as I can tell. I'm just trying to figure out why the "ignition on" wire is getting *any* voltage let alone 10v with the "ingition off".

Is it possible that the wiring has been screwed with on this thing, or do they all normally carry that kind of voltage with the ignition off? The stock harness doesn't look hacked, and the fuse panel doesn't look hacked either.

[langer1]

Your volt meter is not on ground.

[gba88]

Your volt meter is not on ground.

So I'm getting incorrect readings by grounding the meter to the ground that comes out of the stereo harness??

[langer1]

So I'm getting incorrect readings by grounding the meter to the ground that comes out of the stereo harness??
Could be if it's not connected at the other end.

what is the problem your having?

[gba88]

Could be if it's not connected at the other end.

what is the problem your having?

No problem to speak of, just don't want to mess up the radio when I finally put it in.

The main issue is that the violet/white wire has about 10v on it with everything OFF. With acc or ignition ON, it has 12.xxv.

I've installed many stereos in different cars before, but never came across a switched ignition wire w/ voltage in the off position. Thanks for the continued help by the way!

Edit: I'll have to double check all of this later today (at work now)....... I may end up just running a new switched wire just to be safe.
Just didn't know whether or not this was "normal" for a 96.

[langer1]

I'm just guessing but if your batterys is not going dead then your meter is auto scaling and the voltage your seeing is 1.07 volts not 10.7 volts.

With 10.7 volts the radio would still be on.

[gba88]

I'm just guessing but if your batterys is not going dead then your meter is auto scaling and the voltage your seeing is 1.07 volts not 10.7 volts.

With 10.7 volts the radio would still be on.

Battery seems fine, no other problems at all. I'm using a digital meter though, so I'm pretty sure about the 10 volts that it's reading. I'll post again this evening with any new findings :)

[langer1]

Think about this, all your accessories are tied together at some point after your ignition switch. So if your radio POWER lead has 10.7 volts with the key off so would ALL your accessories.

[gba88]

Think about this, all your accessories are tied together at some point after your ignition switch. So if your radio POWER lead has 10.7 volts with the key off so would ALL your accessories.

Good point. I guess either something's up with my readings/meter, or it's just the wire that is in the radio bundle.

[gba88]

Ok.... solved. As it turns out, everything is fine. I think I was getting too technical in my measurements and methods. My digital multimeter was actually throwing me off. If I would have just used the old testing lightbulb, I would have been fine.

Apparently, if you don't have something connected to the ignition wire, it retains a certain amount of residual voltage that is not drained. I figured this out by connecting my DMM along with my old 12v testing probe. Of course, when the bulb was hooked up, it drew all of the voltage out of the wire and the voltage dropped to 0 with the ignition off.

So connecting the DMM to the ignition wire alone was not enough to drain the residual voltage that was left in the ignition wire(it just continually read 10V). And back to the original post... the blue wire w/red stripe was the dimmer that was connected to the dash lights. Thanks again for the responses :)