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Car Forum / Driving, Maintenance, Tuning / RVs / March 2007Trailer Lights Wiring
The other day I had what I think is a great idea for vehicles that need the special adapter to add trailer lights. The original problem is that in newer vehicles the current to the brake and turn signal lights is monitored and simply adding extra lights in the circuit can cause problems like fast blinking and more. In general, each brake light uses about 27 watts. Add up the bulbs and that is the load that the computer expects to see. My idea is to use the regular lights in the tow vehicle, and in the trailer use the new LED brake and turn signal lights. These only draw about 5 watts and I doubt it would be enough to raise any flags to show a possible failure. Sooooo........... Anyone try this? The running/clearance lights shouldn't have to be changed since they are not computer controlled but are simply turned on by an old fashioned switch. Wadda Ya Think? Tony I've not seen any computer controlled lights but I have seen the symptoms you mention. I always assumed it was a weak flasher relay. Remember when you used to be able to pop in a heavy duty flasher? But back to your point. Yes, LEDs will work great. You can find replacement units that pop into a regular socket on Ebay. Or you could replace the trailer lights and lenses with LED models but they are fairly expensive. > The other day I had what I think is a great idea for vehicles that need > the special adapter to add trailer lights. [quoted text clipped - 26 lines] > Newsgroups > ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- >I've not seen any computer controlled lights but I have seen the >symptoms you mention. I always assumed it was a weak flasher relay. >Remember when you used to be able to pop in a heavy duty flasher? These days you can get a variable load flasher and solve the problem. > The other day I had what I think is a great idea for vehicles that need > the special adapter to add trailer lights. [quoted text clipped - 12 lines] > > Sooooo........... Anyone try this? I've always added a small relay to feed a direct line from the battery to the trailer lights. That isolates them from the vehicle. Easy and effective. >> The other day I had what I think is a great idea for vehicles that >> need the special adapter to add trailer lights. [quoted text clipped - 16 lines] > to the trailer lights. That isolates them from the vehicle. Easy and > effective. That's exactly what I did. I bought 2 generic automotive relays (relays good for A/C clutches, old horns, power windows...) wired them up. While playing with it, I saw how much of a load the extra lights were, and that made them a bit on the dim side. Using the relays and the separate hot wire from the fuse box next to the battery made a big improvement to the brightness of the lights! The running/clearance lights were also dim so I added a relay for them also. What a difference! The only problem with the running lights is that the relay is rated for intermittent use. So I'll order a special relay for that, or I may just see how high a resistor I can put in line with the relay still working. There is normally a large margin there so if the relay will work with only 10 volts (normal is 13.9vdc when running), it may run cool enough that I don't have to worry about it. Thanks, Tony >>> The other day I had what I think is a great idea for vehicles that >>> need the special adapter to add trailer lights. [quoted text clipped - 18 lines] > > That's exactly what I did. I bought 2 generic automotive relays I forgot to explain why I went with the relays instead of the LED's. I have one vehicle used for towing and 4 different trailers. So with the relays in the tow vehicle, I'm all set for towing any trailers. Tony > > The other day I had what I think is a great idea for vehicles that need > > the special adapter to add trailer lights. [quoted text clipped - 16 lines] > to the trailer lights. That isolates them from the vehicle. Easy and > effective. I believe most tow vehicles today that come prewired for a trailer have something similar to this. It's likely a solid state device instead of a relay, but the purpose is the same -- the trailer wiring is isolated from the tow vehicle signals. On a side note, those were not "weak" relay/flasher modules. They were designed to alert the driver to either a blown bulb (no flashing) or an overload/short (flashed very rapidly). In either case, those who undwerstood that could avoid a warning or ticket by getting the bulb replaced or problem fixed. The heavy duty relay/flasher was intended to allow trailer use without the annoying "fast flash". Austin > The other day I had what I think is a great idea for vehicles that > need the special adapter to add trailer lights. > > The original problem is that in newer vehicles the current to the > brake and turn signal lights is monitored and simply adding extra > lights in the circuit can cause problems like fast blinking and more. I got a great answer to my problem from someone in alt.engineering.electrical I've wired it up and it works great. (CUT AND PASTED) You need two relays for the turn / stop function. Make sure the relay you select does NOT have a suppression diode across the coil since it will have both polarities applied to the coil. For the left turn /stop line on the trailer, connect the relay coil between the left turn line on the van and the stop light circuit on the van. If the turn signal is flashing alone, the relay will cycle with the coil ground provided by the stop light bulb filaments. The relay coil current isn't enough to cause the filaments to warm enough to light up. If the stop light is on without a left turn signal, the relay will be on solid with the coil ground being provided by the turn signal filaments. If the brake is on and the turn signal is flashing, the relay will cycle. The source will be the stop light circuit and the ground will be the turn signal bulbs. When stop light is on and the turn signal is in the off part of the flash cycle, the relay will be on with the ground through the turn signal bulbs. When the turn signal is in the on part of the flash cycle, both sides of the relay will have 12V and the relay will be off. The right turn/stop relay is wired the same way, with the coil between the right turn wire and the stop bulb wire. If the trailer has a bunch of marker lights (full clearance light package), you may want to consider a relay for the marker lights too. If it only has the tail lights you probably are OK. |
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