12v Accessory Outlet Relay Bypass Switch

Hello Fellas! I figured I'd post another 12v ACC thread since we don't have enough. This one is for the electrical geniuses out there.

Last night as I was lying in bed, visions of mods dancing through my head..... I pondered if it would be possible to add a switch to bypass the relay for the 12v ACC outlet. Since I like to keep ALL my options open, I want to be able to run the ACC outlet when the bike is on or off, however I'd like to keep the relay in circuit. Say you've been riding all day and just noticed your phone is almost dead. While you stop for a quick bite, you need to charge your phone but you don't want to leave the bike ignition in the "ON" position, with the lights, pumps, and everything else powered. Flip a switch and the 12v power is routed around the relay to energize the socket. Lock it in the frunk while it's charging and in to In 'N Out you go.

But why wouldn't you just skip the relay all together and wire it directly to the battery?

Well, 99% of the time the relay would be in circuit switching the ACC outlet with the Ignition; hassle free. But those odd times when you need an outlet but can't necessarily leave the bike running, flip the switch and voila!

So the schematic in my head is as follows....
Normal battery - fuse - relay - fuse - 12v socket configuration, but add a 2-position switch between the battery and the first fuse with a wire connected from the other side of the switch to the fuse after the relay. Therefore, bypassing the relay and creating a direct-to-battery config.

I hope this makes sense. I guess if anyone can't read my mind, I could draw it out.

Will this work? Let me know.

Yes, a double throw switch that connects the outlet to relay power or hot battery power. Good idea.

Just wire it unswitched but fused of course. I never have seen a need to run any cig plug device off ACC but then all I use it for is charging cell phones and hooking up a battery tender/charger.

That would work but you will need a switch that is rated for higher amps than the fuse so it doesn't burn up before the fuse would blow. A lot of switches are rated for low amps since mostly they are used to control a relay.

If you are just running an accessory outlet, it shouldn't be a problem doing it without a relay or switch. Even with a USB port, which draws very small power even not in use, it's not going to cause any problem, unless you park it for long period of time. IN which case, it should be on a tender anyway.

I have one switched and one unswitched. Same for USB's.

Did you ever do this? Sounds like a good idea, wondering how you made out with it...

I did do this and it has worked perfect so far. Unfortunately, I didn't take any pictures while I was doing it, but it basically worked just as described in my original post. I couldn't find a lighted switch in the style I wanted so I just added an LED next to the switch that would illuminate whenever the socket was energized. Here is a picture of the setup in my frunk.

Josh H said:

I did do this and it has worked perfect so far. Unfortunately, I didn't take any pictures while I was doing it, but it basically worked just as described in my original post. I couldn't find a lighted switch in the style I wanted so I just added an LED next to the switch that would illuminate whenever the socket was energized. Here is a picture of the setup in my frunk.


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LOOKS GOOD!!! I could have not done a better job myself...

I would have been nice if you provided us all with a "Parts List" for all the items that you used to do this and where to get those items. Just in case someone else wanted to do the same thing.

Me personally, I bought a Cigarette Lighter to USB adaptor and a Phone Charging Cable from the 99¢ Only Store. I have them stashed away above the tool kit. The diameter of the cable is small enough that I can route it out and close the Frunk lid without effecting it. Then I plug it into my phone that's on my belt and charge it while riding. I have not needed to use it, but it's there if I need it.

That is awesome. Because I am an utter goof with electronics... I need to ask a few questions (plus I have my bike nuded right now doing the sub harness and I'm going to do the ACC too now after seeing what you did). When you say above normal battery to fuse, is the fuse just inline on a wire? Something like what I have seen on my heated grips (Oxfords) or on a garmin GPS moto mount?

How about a quick drawing?

cjohnvt said:

When you say above normal battery to fuse, is the fuse just inline on a wire?

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Yes, exactly. I'm at work now, but I'll try to draw something up tonight. Maybe this weekend I'll take it apart to clean and snap some pics.

Cool idea!

This got me thinking, since I'm extremely absent minded, about putting the accessory socket on a time delay relay. I could leave something charging, but never long enough to drain the batttery, because it would shut itself off after 30 minutes or an hour or whatever.

Sweet. Thanks!

On a side note, it is amazing how much grunge gets caught up under the body panels and the frunk, etc. That's one side benefit to doing your own work, cleaning the nooks out.

maxwellian said:

Cool idea!

This got me thinking, since I'm extremely absent minded, about putting the accessory socket on a time delay relay. I could leave something charging, but never long enough to drain the batttery, because it would shut itself of after 30 minutes or an hour or whatever.

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Hmm, while I'm sure this would definitely work, I'm not really convinced it's worth it. Then again, a lot of people didn't think putting a bypass switch inline was worth it either! I have left mine on before for several days at a time and the battery had no problem starting the bike right up. Think about it, most devices know when their battery is full and trickles or stops the charge completely, therefore minimizing the draw from the battery. I think you'll be fine without it, but if you're anything like me, you're always thinking of ways to make it better!

So, this is a very basic drawing of what I did to add the bypass switch. I will go in further detail after snapping a few pictures and getting part numbers for the switch, relay, etc. The only thing I added to this was a LED just before the 12v socket to indicate whether the socket was energized or not.

Sorry, fellas! I had to delete the picture of the Basic Diagram because it did not match the correct wiring diagram of the bike. I will update later with a correct diagram.

Thanks Josh, thats killer. I can totally seeing my wanting this type of functionality at some point. Pics would be great, I can see some head scratching on my part already.

So, I'm assuming the harness is the honda sub harness? If so, it looks like the entire harness will be switched now

Josh H said:

So, this is a very basic drawing of what I did to add the bypass switch. I will go in further detail after snapping a few pictures and getting part numbers for the switch, relay, etc. The only thing I added to this was a LED just before the 12v socket to indicate whether the socket was energized or not.

View attachment 17036

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The only concern here is that the switch and it's wiring are not protected by a fuse against shorts to ground. Having the fuse at the battery or closer to the battery would provide more protection.

cjohnvt said:

So, I'm assuming the harness is the honda sub harness? If so, it looks like the entire harness will be switched now

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Yes, that is the Honda Sub-Harness and the Honda Relay, but the harness is not switched by the Bypass Switch. The switch is an ON - ON, Single Pole, Double Throw (SPDT) switch which is never really OFF. It switches the 12v power to Direct from Battery ("ON" in the drawing) or to the Relay ("OFF/IGN") which is switched by the ignition.

670cc said:

The only concern here is that the switch and it's wiring are not protected by a fuse against shorts to ground. Having the fuse at the battery or closer to the battery would provide more protection.

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You know what, Greg, I think you're right. I'll have to go back and look at the bike to confirm, but I believe I did put the switch just after the 7.5A fuse, and just before the relay.

Right, got it. I'm hoping to get a bulk of this accomplished this weekend. Still need to score the acc outlet.

One thing that is confusing, from the relay to the switch, is that path behind the fusebox? Sorry for all the questions, first time doing anything like this.