Dr. Hess
Dr. Hess SuperDork
4/27/09 11:11 a.m.

I'm building a trailer to pull behind my bike to get some of the weight off for road trips. The trailer is coming along nicely. Frame all welded up, slammed (yo), shortened, narrowed, tubbed with wheel wells I made from composit ("Composit" sounds better than "cardboard and fiberglass"), and I haven't weighed it, but I'm guestimating it at about 90 lbs empty (MT) with axle and wheels.

So, I need to do the lights pretty soon. Now, what I've been thinking to keep the electrical load low is to go with LEDs, and use the "bulb" cluster from those $5 HF 3 AAA cell flashlights. They even go on sale for two for five. The problem is that a Harley has a tail light, brake light, and two turn signals, or three elements total if you think of a single side. I think trailer lights have two elements, and I have come up with a drawing to use ballast resistors to drop the light output on the bulbs to 1/3 power for a tail light with a full on for the brake, but I don't know what to do with the turn signal. I think I could add a transistor and switch the brake light brightness off when the turn signal was on, but that would look a little funky with the trailer turn signal flashing off while the bike turn signal was on and vice versa.

I also thought of making the circuit a 3 level, or low for run, higher for brake and full on for turn signal, but I think I would prefer the brake light to be brightest.

How do regular trailers work? I saw one today that flashed the same brightness when the turn signal came on as with the brake, and with both, it was brake on one side and dim/bright flashing on the other. I don't want to get another add on box on the bike. For one thing, they want a bill for them, and for another, I don't want to try to find a place to put it. I also want to keep 4 wire compatible so I can just plug it into the Truck's harness if I want to use it there. The 4 wires on a standard trailer plug are brake, left, right and tail, with ground through the hitch, right?

curtis73 Reader
4/27/09 2:41 p.m.

In a typical setup (which uses 1157 bulbs) there are simply two filaments inside the bulb. One is a higher wattage and handles the brake and turn duty. The other is dimmer and handles taillight duty.

You can't use a resistor on an LED cluster. LEDs don't get dimmer as you reduce voltage, they just reach a point where they fail to emit light. They make light by a high-frequency thingamabob that is supported by a voltage range. In actuality they do get a bit dimmer, but not really that you can tell with your eye. You need to choose LEDs that put out a known amount of light in order to make the difference between brake/turn and tail.

Since you have the separate turn signals, you have a couple choices in my opinion. You can get (or construct) a box that converts the separate signals into one wire. It consists of relays and diodes for switching the brake light on and off (to make a turn signal) without feeding back and flashing the brake lights on the bike when the turn signals are on. Then you can wire the trailer with the standard 4-lead setup where green is right turn/brake, yellow is left turn/brake, and brown is running.

The other option that I see is to make your own wiring and simply run a wire from each component to a duplicate on the trailer. Run a wire from the brake light circuit to a couple brake lights on the trailer. Run a switched 12v wire for some running lights, and then run wires from the turn signals back to some turn signal lights. Its a little more complex to wire, but less complex to logic out.

mw Reader
4/27/09 3:17 p.m.

On a stanard trailer plug, ground does not go through the hitch. It is one of the 4 wires.

You can just get one of those 5 to 4 trailer wire adapter things. I'm not electrically skilled, so to me it is a magic box that converts your running, brake, left, right, ground wires into 4 wires that hook up to a 4 wire trailer plug. They are $10 or so and then get a trailer light kit from HFfor $20.

Dr. Hess
Dr. Hess SuperDork
4/27/09 4:40 p.m.

Humm. Yeah, white on my Truck connector appears to be Ground. OK, looks like I'm gonna need a 5 to 4 wire converter. Ten bucks, huh? That doesn't sound too bad. I wonder if HF carries them. The aftermarket sets for HD bikes are in the one bill range. Must be a heck of a fancy plug on it.

HF has a LED trailer light set, but it's like $40. I think I can do it with my flashlight sets. If I have to, I can cut the circuit board into two sets of LEDs. I'm going to experiment with the voltage and see what happens here, but I'm pretty sure that dropping the voltage is going to drop the light output. These little flashlights put out pretty good light and only draw 1/2 Watt. I'd say they were brighter than an 1157, which is what, 21 Watts on the high element? Something like that. My $140 HF trailer came with a standard light set with harness. I just want the LEDs for the low current draw, saving like 30 watts.

oldopelguy HalfDork
4/27/09 7:34 p.m.

One of my favorite trailer wiring sites: http://www.marksrv.com/wiring.htm

Trailers wired-up American style use the same filament for the turn function and for the brake function. European-style they do not, but finding plugs for Euro trailer wiring in the US is difficult and it would defeat the ability to transfer the trailer to the truck. http://stores.ebay.co.uk/Towing-and-Trailers-01909-473749/Plug-guide-and-trailer-wiring.html

The GRM way to convert your current "4-wire" set up into a "3-wire" set-up involves a couple of small 12V relays. The coil on most small 12V relays is roughly 500-900 ohms of resistance, which translates to 15-50mA of current required to energize the coil and close it's mainline contacts. (Compare that to an incandescent light bulb which draws 2-3 amps at 12V to light up and has roughly 1/3 ohm of resistance.) If you wire one side of the coil on the relay to the hot supply to the brake light and the other side of the coil to the hot supply to your left taillight when either is powered-up the coil will effectively ground through the other and pick-up. When both are on, the coil will see 12V on both sides and drop out. Then run a hot wire from the battery, through a fuse, to one side of the mainline contact on the relay, then from there to the yellow wire on the trailer 4-flat plug. Repeat on the right side running to the green wire. Add another relay if you choose (I would) and use the taillight supply to power a relay to send power to the trailers running lights.

If done right you have one fuse you can pull that supplies power to everything on the trailer, and everything will work as it's supposed to. The trailer will also be wired correctly to hook to your truck and work as designed.

Dr. Hess
Dr. Hess SuperDork
4/28/09 9:40 a.m.

Thanks, oldopelguy. Pretty clever on the two relays. I still want to use LEDs to drop the electrical load for the running lights. I kinda like that one fuse for the trailer concept. I'm going to have to think of a solid state solution with LEDs, a plug-n-play harness for the bike and still keep the portability.

My hitch came in yesterday. Two bills from MCHitch.com for a powder coated receiver hitch. I could have made my own, but it would have taken me a week at least and it's nice to have someone else do the R&D every once in a while.

Jensenman SuperDork
4/28/09 10:31 a.m.

Doc, the LEDs from the flashlights are all well and good, but have you looked into these? http://www.superbrightleds.com/tail-brake-turn.html

$4.99 for an 1157 replacement with all the hard work already done, goes right into a standard two contact bayonet socket. They are even available in colors.

Kramer Reader
4/28/09 10:52 a.m.

Truck stops have 12v LED marker lights, in red and amber. Usually round, but some oval. Find a good auto/truck parts store and dig thru their catalog.

Dr. Hess
Dr. Hess SuperDork
4/28/09 11:22 a.m.

That looks like a pretty good deal. I think I'll get some of those. Final costs would be about the same as making my own from the flashlights. I might even pick up some extras for the Sporty. Since I went Megasquirt on it, the electrical system is pretty maxed out. Might have to get one of those flasher controllers for it too. Now I just need to deal with the 5 to 4 wire conversion for my bike.

Dr. Hess
Dr. Hess SuperDork
5/27/09 11:40 a.m.

OK, I got my superbrightleds.com lights. I got my Hopkins (AKA "Hoppy") 5->4 wire converter, wired it up in a real neat, clean install. Then I found out the Hopkins only puts out 8 volts on the turn signal lines, not enough for the regulated LEDs to turn on. A call to Hopkins was useless. The "tech" said that it needed to draw an amp to turn on the "full voltage." So I experimented with a 1157 and he was full of E36 M3. The Hoppy adapters are craptastic. He suggested the connector with the separate line to the battery. After dealing with this piece of E36 M3, I think I'll avoid further Hopkins accessories. My Truck also has a Hopkins 5-4 wire converter and has the same problem when I hooked up the trailer to it.

So, for my trailer lights, I think I'm going to experiment with some transistors mounted in the trailer. I think I can put a 2n2222 in there so that when the 8V comes down the turn signal line, it shunts the 12V from the tail light line (on all the time on my bike) over to the turn signal line. That will work as long as the tail light circuit is energized, that is, just drive with the lights on when pulling the trailer. Either that or I'll have to rewire the bike and the Truck.

erohslc New Reader
5/27/09 3:48 p.m.

I'm thinking that 2N2222 will not handle the current and/or power. But a TO-220 cased unit like TIP22 or TP3055 should do. Sounds like a job for a relay though. One of the little 'universal' Bosch cubes. No heatsink, no bias resistors, no bypass capacitors, no VCE(sat) to deal with, etc.


Dr. Hess
Dr. Hess SuperDork
5/27/09 4:29 p.m.

Yeah, I thought about a 2N3055, as I have a couple of them in one of my parts jars. They're a real work horse. I think you can push 30-35 watts RF out of them with a good heat sink, but in this case, I think the 2n2222 will be OK because the LED tail lights only draw 80 milliamps on high. I'll make an aluminum heat sink for them just in case. Anyway, I can try the 2n2222's and if they blow, slap the 2n3055 on.

A "megasquirt vendor" NOT DIYAutotune.com, but another one that I'll never deal with again, put together my first MS1 3.0 board and used a 2n2222 to drive the VVT solenoid. They claimed 20 valve experience, said they did these before, this was a standard option, etc. You know what happens when you run an amp through a 2n2222? POOF.

Dr. Hess
Dr. Hess SuperDork
5/27/09 7:59 p.m.

So, made my 2n2222 circuit. Output voltage on it was 8V, not enough to trigger the LEDs, and about the same as the Hoppy. Now we know what's inside the Hoppy. Looks like it's going to be relays, if I can find some that will kick in on 7-8V.

billy3esq Dork
5/28/09 3:42 p.m.
Dr. Hess wrote: You know what happens when you run an amp through a 2n2222? POOF.

The technical term for that is "letting the magic smoke out."

Dr. Hess
Dr. Hess SuperDork
5/28/09 4:23 p.m.

Except I think it was 10 amps, now that I think about it. It was a lot. I wound up using the VB921 coil driver IC instead, which works fine at that and has built in flyback too.

I found some 9V relays at Crap Shack. Of course, I have to go to two Crap Shacks to get two relays. I also drew up a schematic to use the relays and a DPDT (which I found in my box of junk last night) switch so that if I want to pull the trailer behind something with a real 4 wire system, I can just flip one switch and be back to wired normally.

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