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Okay, after reading through the search topics on this I've decided to make it my personal crusade to hunt and defeat the radio circuit gremlin that has plagued our beloved automobiles for too long.


....okay, maybe that was a bit dramatic. In any case, the issue at hand involves the radio circuit with multiple different brands of aftermarket head units. The radio will stay on after the vehicle is shut off until another specific power draw (usually wipers or cig lighter) are used. At this point, the radio will shut off. I have seen multiple posts regarding this subject with no actual fix posted (coincidentally, if there is a fix I'd like to know what it is). Fortunately, automotive electrical diagnostics happens to be my specialty, so I WILL find the solution to this problem. I will report my findings in this thread.

The reason this is happening is there are various capacitors on the accessory line that don't discharge quite fast enough. Many aftermarket head units can keep working even when the accessory voltage is very low because they just use power from the constant-power wire instead.

All you have to do to make this problem go away is put a little extra load on the accessory circuit to drain the capacitors faster. You may notice that if you leave the wiper switch on, the problem doesn't happen. Or if you leave a cell phone charger or something plugged into the cigarette lighter.

So here's what you do -- just take a standard automotive Bosch-type relay and connect its terminal 85 to an accessory-switched power wire and terminal 86 to ground. You don't need to connect anything to terminals 30, 87, or 87a (if present on the relay). The load of the relay coil should be enough to make the problem go away.

The issue in the circuit has to do with the wiper system in particular. Once the wiper motor is unplugged the system acts as normal. However, with it plugged in there is a slow 12V bleed off that occurs. I'm not certain as of yet whether or not this is coming from within the wiper motor assembly or the intermittent wiper control unit. In either case, I highly doubt this is normal.

Hmm, maybe the capacitors are in the intermittent wiper control unit. There is a little bit of electronic circuitry in there for sure. Aside from that and the radio, I don't think there are any other electronic (as opposed to simply electrical) things on the accessory circuit.

I do believe it's normal on our cars. It just doesn't show up in stock form because the stock radio won't run with low voltage on the ACC line. It happens on GC/BFs as well as first-gen Legacies.

Are you unsatisfied with the solution of just putting a little load on the ACC circuit? If the relay seems inelegant, you can always just use a resistor... Try a 1K resistor between ACC and ground instead.

The circuit contains the wiper/washer system, cigarette lighter, radio, and input side for the main radiator fan relay. I'm finding it difficult to believe that the system normally has a stored load with the vehicle completely turned off. The bleed-down on this is actually quite long with no loads on the system (20+ minutes with the radio unplugged). I've never witnessed this on ANY other Subarus with ANY aftermarket head units.

Since I'm not convinced this is a normal condition, I'm not applying what may be a band-aid to a larger problem. I'm betting that there is an issue within the intermittent wiper module portion of the switch assembly, but I'll need to do more diag to find out whether or not my theory is accurate. If it is a normal condition, I've got another head unit with an interference cancellation box on the ACC power wire that I'll install.

Oh, and here's the best part.

1) Turn Ign on with radio on.

2) Unplug wiper motor connector from underhood.

3) Turn Ign off - radio shuts off immediately.

4) Plug wiper motor connector in with key off - RADIO TURNS BACK ON.


It's either in the motor or the switch assembly.

Oh, huh, that's funny that unplugging the motor makes it go away! I didn't read your post carefully enough. But if it's a capacitor discharging, you'd expect it to come back on if you reconnect the wiper motor, wouldn't you?

Every properly-designed electronic device has decoupling capacitors on its power rails. I would expect quality amplifiers to have pretty big ones, in fact, so they could the transient load that comes with every bass thump.

And without any load, you'd expect those caps to take a long time to drain, wouldn't you? Have you watched the voltage as that happens? It's not like it stays up around 12 volts for 20 minutes; the voltage is decaying, and in fact gets too low to operate most automotive electrical or electronic devices fairly quickly.

Like I said, this does happen on Imprezas. It happens on my current 99 Impreza and happened on my 97 too. And it happened on all four of my first-gen Legacies that I put aftermarket head units in.

Maybe newer Subarus have something else on the accessory circuit.

But if you're convinced there's some defect in your car that's not by design, I'll wish you luck finding it. I'm eager to hear what you find. I'd definitely start looking in the intermittent control module (which is built into the stalk), since that's where the caps are likely to be.

Yes, but every properly designed circuit also has diodes to keep the capacitors from discharging into the rest of the system. My suspicion is that a diode in the switch may have failed short after a long enough period of sustained circuit heat (350,000+ miles of driving in Oregon).

Whether this is caused by failure or design, I think the simple solution for the problem is to install a known good diode into the hot side of the switch/motor circuit. After all, a new switch is nearly $200, which is a little heavy for a problem of this minute importance.

You don't usually want a diode in series with the power supply. It's certainly not true that every properly-designed circuit has one. That diode would be wasting power and dropping voltage.

The wiper circuit fuse is rated at 20 amps. Even if we imagine that they designed in a 300% cushion, that would be 5 amps running through the diode. Even a Schottky diode would be dropping close to a full volt at that current.

I may be wrong, but I wouldn't expect to find a diode in there.

No, you're right. A diode won't suffice for what is going on. Still, something is not right. According to what you're saying, the probability is that every car (not just every Subaru, every CAR) should exhibit this problem. Yet, I have owned well over 20 different automobiles in my life, most with some form of aftermarket head unit installed. None of them have had this issue.

A friend of mine who's better on the electronics side of the gap than I am (I'm best with 12V DC electrical) gave me another idea: Faulty ground popping up somewhere in the system. I'm wondering if I shouldn't check the ground path of that capacitor to see if it's higher than it should be (ie. motor starting to get high resistance with age).

I think most cars have more on the accessory circuit than just the wipers, cigarette lighter, radio, and fan relay. The problem we're talking about is happening because there's literally nothing other than the radio present to drain those caps. And maybe Subaru does put unusally big caps in the intermittent wiper control unit. Maybe they're somehow used in the timing circuit.

I don't follow how a bad ground would cause this without also causing problems with the wipers, but let us know what you find.

Okay, as far as I have discovered this is a normal condition to this particular car and possibly other Subaru vehicles. The reason behind my theory is this: No other vehicle line that I know of has the wipers powered from the accessory circuit. The capacitor in the wiper switch has no proper ground path once the wipers are turned off, so it sends its power back into the rest of the accessory circuit. With the OEM radio this is not an issue, as it sucks power like a dinosaur. However, the efficient new head units draw much less power on the circuit and therefore will stay on for extended periods.

I hypothesize that a head unit with the noise-cancellation box built into the power wire circuit will not suffer from this fate as the resistor pack inside the box will draw the brunt of the capacitor's remaining power. Another option would be to put another large load into the accessory circuit (something else for the capacitor's energy to draw through). This should be done carefully, as reistance creates heat (you don't want this thing set some place where it could cause a fire). Subaru could have easily fixed this issue with a resistor inside the wiper switch that ran between the power side of the resistor and a ground. I'm also do not think the non-intermittent wiper equipped cars had this issue, as I do not believe there was a capacitor in that system.

To conclude, it is my belief that vrg3 was right....again. Thanks for letting me bounce a few ideas off of your head, though. I'm going to install my CDA-7892 and see if it won't draw enough power to keep itself from running after shut-off.

Hehe, happy to help.

I don't think it's a question of how efficient the head units are; I think it's just that the aftermarket head units will operate off the constant power feed as long as the accessory feed has at least a couple of volts on it. But, anyway, that's neither here nor there.

You don't need a large load though. Really. A 1K resistor should be fine. It'll only radiate an eighth of a watt.

And you're totally right that Subaru could have just stuck a resistor in the intermittent wiper control unit and avoided this whole situation.

Another idea I thought of was simply installing a relay that would open the ground circuit for the capacitor when the ign was turned to off. This would leave the capacitor charged, which I'm not too enthusiastic about, but it is a solution.

Yeah, that'd work... It'd consume power all the time when the ACC was on, though, just like a resistor would. If you powered that relay's coil from ACC rather than IGN, it'd work even without having it wired into the intermittent wiper circuit.