Accessory Voltage Question

[Dusty T.]

I posted this elsewhere, but didn't get too many responses. I was hooking up a couple relays to control on/off power to a CB and my stereo. When using a voltage meter to verify the correct ACC wire, I noticed that the ACC circuit is getting a very small amount of voltage with the ignition off (even with the key removed). It looks like the cigarette lighter plug is on the same circuit as well since it along with ACC power is cut when the ACC fuse in the dash is removed. Plus, it also shows that same small voltage as well.

Would anyone here with a pre '05 tacoma check their cig lighter with a volt meter with the ignition off and let me know what you come up with? It seems odd, but there has never been a problem with the battery being drained after several weeks of sitting, and the wiring was all original when I noticed this.

Thanks!

 

[soonenough]

I know this is probably a stupid question, but was anything plugged into the lighter during the periods of the truck sitting? Because if not, there's no reason that the battery would've been drained, regardless of any voltage at the lighter. Unless there's something plugged in allowing current to flow, the charge on the battery shouldn't change.

It does seem weird though for the lighter to be getting a small amount of voltage. I would think it would either be getting 0 volts or ~12 volts. The only thing I can think of that would cause that is if there's something connected to the lighter circuit that is acting like a capactor, maintaining a very small charge after being disconnected from the battery.

 

[Dusty T.]

Nope, nothing was plugged into that circuit at all. I even disconnected the aftermarket stereo harness adapter plug to see if power was being backfed from that. Also disconnected the harness that feeds through the ignition switch, and was still getting around .10 volts. I did plug in a small cooler into that lighter plug which dropped the voltage to zero, and tested the current flowing from the battery with the ignition off and the cooler plugged in and "on". It never read above 18 milliamps and went up maybe two milliamps with the frige connected. From what I understand, this is well below a normal load when not in use.

Yeah, you'd think it would read either zero with the key off, so I was wondering if this is just a feature of these trucks. One other person on a different board got this same voltage reading- was wondering if anyone else has this? I don't think it's enough voltage to push enough current through to drain the battery noticeably faster either way but it is strange.....

 

[climber-420]

Is it always on with the truck off? Maybe check the fuse box under the hood and look for a wire connecting two fuses. That's a simple trick people use to keep the accessory outlets "always on".

 

[soonenough]

Nope, nothing was plugged into that circuit at all.

I don't think it's enough voltage to push enough current through to drain the battery noticeably faster either way but it is strange.....

But what I'm saying is, regardless of whether there's 0.1V, 1V, 12V, or 100V, if there's nothing plugged into the outlet, there's no reason that your battery should be drained. Current flow is what drains the battery, not the presence of voltage. Or am I missing something?

I'm not trying to sound like a jerk, I'm just making sure I'm understanding you right.

 

[Dusty T.]

But what I'm saying is, regardless of whether there's 0.1V, 1V, 12V, or 100V, if there's nothing plugged into the outlet, there's no reason that your battery should be drained. Current flow is what drains the battery, not the presence of voltage. Or am I missing something?

I'm not trying to sound like a jerk, I'm just making sure I'm understanding you right.

Hey no problem- hopefully the following clears things up a bit. This whole thing came up because I am using this ACC circuit as an on/off signal to power a small relay I'm adding for some accessories under the dash. Of course, that ACC circuit would only be powering the little coil on the relay which is a very small current draw, however there will still probably be some current drawn through it with the ignition off via the .1 volts that is present.

Then I got to thinking the "what if's", like what if I left something plugged into the lighter plug (which so happens to be on that same ACC circuit that is signaling the relay I've added) while camping somewhere and forgot to unplug it after sitting for a few days- potentially resulting in a dead battery- though I'd imagine that small amount of current is negligable. I would think that Toyota designed the lighter plug to be completely cut off with the ignition off, so it seems strange that it is still showing a fraction of a volt when in fact it should be off. Seeing this leads me to believe that A- this is just normal, and just about all Tacomas are wired this way, or B- there may be an electrical problem with power bleeding through from another source.

I'm really just looking for a couple folks here to quickly check their voltage at the lighter plug, post up what they get, and hopefully come up with the same results I am getting. At that point, I would just dismiss this as a non issue. It's probably a non-issue anyway but I'm a bit curious about this either way.

Thanks for the input- I hope that made some sense. I have trouble elaborating sometimes....

 

[soonenough]

Ahh, it's all making sense now; I see what you're talking about. Sorry, I wasn't putting two and two together

I'd be happy to check mine with a voltmeter, but it's not a pre-'05 model, so there may be a difference. I don't remember getting any voltage there with the ignition off when I installed my CB and 2m/70cm radio, cause I know I checked it, and I'm sure I would've been thinking exactly the same thing you are - "that's weird".

 

[keezer36]

I know you want to hear from someone with an '02 Tacoma - sorry. But I can tell you this; these spurious voltages of such small potential are of no concern. They are a result of the quality of components in the vehicle, mainly their insulating properties. This is not to say that the electrical components of the vehicle are cheap, they are adequate for the job they need to do. Nothing in your truck is, relay or otherwise going to be tripped by a tenth of a volt nor will it drain your battery anytime soon (months). You could probably find these low voltages at other areas on your vehicle and on other vehicles. Pull a tail lamp and see if you get anything at the socket with the switch off.

 

[Dusty T.]

Keezer-

Actually, I was thinking anyone with an '01-'04 tacoma would be able to test for this. Heck, a '97 to '00 would probably do as well. It would be interesting to see their findings anyway....

I did a quick check of other circuits in the fuse block when I originally found this and came up with either zero, or 12.XXX volts. Nothing in between. Yeah, it is going to be pretty difficult to draw any significant amount of current with such a low voltage source as that, and with everything wired up it hasn't been enough to trigger any of the relays, and all the in-dash electrical I did is working as I intended.

You're right, it is probably some bleed through from another accessory such as the ECU, cruise control, or other system. Who knows?