Powering tail light after bike is turned off

I am sure this has been asked before, but I can't seem to find an answer so I'll ask again.

I have my XR600R street legal, but just running on AC. I'll be converting at least the brake / tail light, turn signals, and horn to DC.

So the law says that when the bike is turned off, the tail light must be capable of remaining on for 15 minutes.

How do you control the taillight since it will be connected to the battery. When the bike is turned off do people just let the tailight stay on and drain the battery, then charge back up agian when the bike is running? That doesn't seem like a good idea. So is the only other option to put a switch.

Just wondering how others have done it. Thanks.

I have an old Baja Designs DS kit on my XR600. It has a switch on the handlebars/top clamp. You need the switch, because batteries don't like to be drained flat. I've killed mine by forgetting to turn the switch off.

I have no battery at the moment. I'm going to change to a sealed lead acid battery, aka SLA, aka GelCell. The Nicad that the kit came with just plain sucks. Seems to get killed every six months or so.


Simply put a switch in on one of the DC leads from the battery to the light(s). However, you have no way of charging a battery witout a regulator/rectifier (the stock unit is only a regluator). You can basically build your own dual sport kit if you buy a reg/rec and a small nicad battery pack. I've had my Baja Designs battery pack (with my Baja Designs DSK) for about 4 years now and it's still going strong.

Thanks for the info. I don't have a problem putting the system together to convert it to DC. I just wasn't sure what people did about the taillight.

I already have a complete DS kit on my bike that I wired myself. What I was thinking is that I could put the tailight circuit on the parking light portion of the headlight switch (its not being used right now). Is this how these kits are normally wired? Then I just have to remember to always turn off the switch when I park the bike. I think this would work. I am also still undecided if I want to run a battery pack or a capacitor. I have a couple of large caps sitting around that I could use. I have a 56000uF, a 68000uF, and some smaller 22000uF all at 16v. I'll have to do the math to see what will work.



The stock DSK's are all wired after the battery, IE. everything gets DC voltage. The bar mounted switch has a first position (ignition ON, running lights On). In this case the tail/brake light runs, as well as the small low wattage bulb in the headlight (not the main high wattage bulb). Turn signals also work off the battery.

A proper sized capacitor will keep the lights from dimming at a stop light with your brakes and turnsignal on. However, I don't think it will last 15 seconds for running lights when the bike isn't running. Capacitors are made for rapid discharge (to compensate when the power supply can't keep up), and as a filter to smooth out the rectified voltage, giving you a nice smooth DC voltage as output. Only a battery will give you the slow release voltage to keep your lights on when the bike isn't running.

All that said, if your bike is already street legal (passed inspection) then don't worry about keeping the lights on with the bike off. It may be the law, but it's not one that's enforced in anyway that I've ever seen. In this case, the capacitor would be just fine.

I'll be hacking my Baja Designs DS kit so I can have some light when the engine quits. I couldn't care less about the tail light being on when the engine is off. However, one time while trail riding at night, I was on a hairy downhill where I was going so slow I had to keep the clutch in. Wouldn't you know it, the engine died. Sudden blackness... I managed to stop without crashing, but I just about had to clean my shorts after that. I'm going to setup a small 20 or so watt halogen that runs off the battery. I don't need a lot of light, just some so there isn't complete darkness when the engine is off. I'll put a separate switch on it, for when I'm on the road. I'm also thinking of adding a switch that will make both front turn signals turn on constantly.

I have the high power stator. It's awesome. I have a 100W headlight, and I have another 100W coil unused. I plan on using it all! If you are so inclined, it's not too hard to wind you own high power stator.

The cap helps the lights at idle. It will not keep it on for more than a second or two at best.

Ya, I know the 15 min. tail light is not enforced, they didn't even check it during my light inspection when I made it street legal. I just thought it was a good idea if for any reason while riding on the street at night the bike dies. I would hate to get rear ended by someone because they couldn't see me.

I'm probably just being paranoid. I really like the idea of having a headlight if the engine dies. I think my headlight assembly also houses a 10W bulb, something like an interior light bulb, which is not being used right now. I may put that back in and wire it to my battery pack if I go that route.

What capacity (mAh) battery pack is common to run turn signals, tail/brake light, horn, and possible a 10W bulb up front? I could figure out the wattage of all my components and see what the minimum I need is, but if their is a good rule of thumb I'll just go by that.

I'm also running the stock 1989 stator. My headlight is a 35W bulb. Though I can build a simple charging circuit that will limit the amount of current the battery draws.


My Baja Designs kit used a AA size 10 cell nicad(800 mah) pack. I have a lot of AA NiMh(1100 mah), but I think that I'm going to try a sealed lead acid (SLA, aka Gelcell). The biggest that will fit above the air box is 1.3 amp hour. Niether Nicad or NiMh, like constant voltage charging. Operated at a constant voltage setup they never get fully charged(maybe 3/4). If you do constant voltage and try to get close to 100%, they will fry for sure.

I was also thinking of having a aux battery that I could add when doing night riding. Maybe a 4.5 AH SLA so I can run the headlight better. Behind teh number plate or something.

If your truly a DIY electrical/mechanical type, you can rewind your stator for more watts. 35 Watts sucks at night. If you do a DC system with a battery, and cut the other loads down with LED marker and stop lights, you should be able to run a 55 watt light without a rewind.

i think rickystator do a 200w stator for about $120 with no exchange. I was looking at the dual light rig they had too on the site. I like it more than the regular dual sport look (but that is just me).. add a SLA battery, blinkers front and rear, horn and a stop light... and you there.. Hold on that little lot would just about double the value of my bike. Darn, back to the drawing board.

I was wondering how the nicad and nimh batteries would handle the constant charging. It would make sense to put a charging circuit that would slow down the charge and eventually cut it off when the batteries are fully charged. Just like a battery charger.

But it sounds like going with the SLA battery is the way to go. I'll probably try the setup without rewinding my stator. I don't do much night riding. I don't have a problem doing the work, it's just if I don't need it, why mess with it. But knowing me, I'll have the stator out and rewinding it soon.


Another question on this topic.

I was thinking of also running my headlight off the DC instead of the AC. Is this common? That way if my engine dies, I'll still have full brightness for a little while (depending on the battery).

I figured with my 35W bulb, I'll be drawing around 3A @ 12v. Then my taillight is pretty minimal, and my horn, turn signals, and brake light are on very little. I remember reading that the stock stator puts out around 50W. So depending on how much current a particular size SLA battery can source, I may be able to charge the battery, and run the headlight without any problems.

But if I go with a rewound stator, and higher watt headlight, then the battery will be the limiting factor unless I go with a very large one. So maybe I am answering my own question here. But it sounds like if you want to run a higher power headlight, then you are pretty much limited to running it from the AC circuit.

Yes, my current system with the rewound stator (2x120W coils) is running a 90/110 H4 bulb on AC with an AC regulator. It dims a bit at idle, but not much.

One coil is for the headlight and the other goes to a DC rectifier/regulator and battery. I'll be running some kind of aux light from the DC system so I don't end up in the darkness should the engine die. I'm converting my turn signals and break light to LED's. Bought 100 red and 100 yellow for $11. I'm thinking of adding a switch to turn the front turn signals on all the time for trail riding.

My stock system has a high side P channel FET to turn the headlight off when the engine dies. I think that's there so they can pass the 15 minute test. A little 800 to 1200 mah battery will only run a 55 watt headlight for a few minutes.

Sounds good. I did some research, and the largest SLA battery I can fit under my seat on top of my airbox is a 3.8 x 2.7 x 1.625. I cut some wood down and kept test fitting it with the seat until the seat would not go down anymore. If I were to cut off these 2 little plastic round stubs that are comming off the seat, then I could go up to 2" on the heigth.

Anyway, I found a 1.2aH SLA battery that meets those specs. I also found a 2.0aH battery that is 3.875 instead of 3.8. So I might try and squeeze that one in. Not sure if I really need the extra .8aH or not.

I also looked up the current properties for some of these batteries. The 1.2aH can source up to around 2A for 15 minutes with a maximum discharge of 6a for <= 5min. Not sure what the voltage would drop too, but it could power at least a 70W bulb assuming you have the stator output to charge the battery while the bike was running.

So I'll have to play around a little and see if I want to run my headlight from the DC side or AC side since I am only using a 35W bulb right now. Maybe I could upgrade to a 55W bulb on the DC. Though this would put a strain on my stator, and the battery would slowly discharge even when the bike was running.

I had a stock stator XR600 with the DHH Acerbis headlight, and it seemed to have a fair amount of light. If you add the Baja Designs regulator, don't you have to "float the ground" on the stator for it to work right? Or, is there a regulator/rectifier that works with the stock set-up? I'm in the middle of building another XR600 that will be street legal when I'm done, so this would save me a bit of time in wiring. I have no problem with running the thing on AC, but I don't know if the State of Minnesota will be a stickler when it comes to inspection. Could a person run a small rectifier to run the horn on the pulsing DC that would result? Or, is it just easier to hang the battery pack, FET, and the BD rectifier?

I looked at the BD wiring schematic on how to use their rectifier/regulator. It states that all DC grounds should be isolated from any AC grounds.

I don't remember if the stock AC setup uses the chasis for a ground or not. But either way, I would just keep the DC ground all tied together. I'll measure the ground and see if it is connected to the chasis anywhere.

I'm fairly sure the AC system grounds through the engine to the chassis. The BD set-up (at least on the earlier systems, pre '90 models) had you removing the ground connection on the stator, soldering a wire to it, and then running that, along side the stock wires to their regulator/rectifier. Everything else split out from there, to the battery pack, lights, etc.

I've been meaning to call BD to see if they can get me the wiring instructions for the old design, just haven't gotten around to it. The ones they have on the website are newer, dual stator wound specs.

Has anyone ever received a citation for not having a tail light that stayed on for 15 minutes with the engine off? In AZ the law requires an electric horn but although I've been stopped for various moving infractions, I've never, in 45 years of riding, been asked to beep the horn just to verify that it works. What cop has the time to hang around for 15 minutes to see if your battery is going to be dead? And ,if he does, won't you just receive a repair ticket (no fine or notice to appear) and be trusted to fix it? If this is part of a DMV inspection, mount a battery on the rear fender for the test then take it off and go without a charging system for the rest of your life!

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