Do you really need a trailer harness converter?

Anyone just splice in a basic 4 wire trailer connector to their 03 mk4 to run lights on a small trailer?

Always pays to do a little science when connecting up to the electric system, see what's required. May be fine to just splice in or you might need to modify the circuit.
A lot of folks with trailer hook-ups, they'll chime in.

Yeah - I asked myself the same question and before causing a brain bleed I ordered one of these... hooked up pretty easy and worked first time.

https://www.amazon.com/gp/product/B0002Q8036/ref=od_aui_detailpages00?ie=UTF8&psc=1

Ok yeah I see now because the stop light is separate from the signals on our cars

Yes, you need a converter. The VW has separate bulbs for the running lights, signal lights, and brake lights and the four wire trailer has running lights, but the signal and brake lights are combined.

You could use relays to make a circuit so that when the brakes are pressed, the brake lights come on, but when a signal is turned on, the corresponding brake light flashes off and on with the signal. You also need the signal lights to flash on and off when the brakes are not pressed.

Notice I say flash "off and on" when the brakes are also on, and "on and off" when the brakes are not on.

This is hurting my brain.

I actually designed a crazy logic circuit that would do the conversion and have the trailer lights draw power from the rear lighter socket. It was all solid state and uses mosfets for the switching. I then realized it was stupidly over engineered and stopped. A few relays should be all you need.

lol Mike and Turbo.... you got a lot further than I did - "I wonder if I can slice it it??? Meh, I'll grab a beer and order the kit"

If it was me, what I would actually do is put different lights on the trailer so it is a five wire system. I think separate turn signals, which should be orange, are more visible to other drivers.

Many times I have not realized someone was signaling in an older vehicle that had the brake and signal combined. This can easily happen if they apply their brakes a few times making both brake lights flash, and then they change to signalling. You have to look at the opposite tail light to realize that one is still flashing and the other is not. Totally stupid system.

Mike_04GolfTDI said:

If it was me, what I would actually do is put different lights on the trailer so it is a five wire system. I think separate turn signals, which should be orange, are more visible to other drivers.

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I did that years ago - put a set of VW tails on a trailer with an extra wire.

I was curious why North American tail lights are so bad, and I was kind of surprised by the reason.

Apparently there are regulations specifying the minimum surface area of a turn signal. Europe has no such regulations.

The unintended consequence of this is that manufacturers often combine the brake and signal light into one large signal light. This meets the surface area requirements.

In Europe, they can make the signal small, as long as it is visible. With today's technology they could have a strip of extremely bright amber LEDs, which are very easy to see, but would be illegal in North America because they don't have enough surface area.

The result is that North American lights are large, but invisible, and European ones are small and more visible.

Mike_04GolfTDI said:

If it was me, what I would actually do is put different lights on the trailer so it is a five wire system. I think separate turn signals, which should be orange, are more visible to other drivers.

Click to expand...

This is not really a good solution though for most, you couldn't tow someone else's trailer, or multiple trailers.. Or you'd have to rewire any of your trailers to match the car. I have a seadoo, snowmobile and utility trailer and need them to work on my car, or truck, or other persons vehicle.

Just do not "cut and splice" anything, you do not need to. The tail lamp bulb holders already have available terminals right there for this specific purpose (the OEM trailer harness plugs in to them, but you can make your own harness if you want).

I had my trailer hitch installed some 9 years ago at U-Haul, and they wired the 4 wire plug at the same time. It still works perfectly.

Nevada_TDI said:

I had my trailer hitch installed some 9 years ago at U-Haul, and they wired the 4 wire plug at the same time. It still works perfectly.

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Curious.
Does the trailer have directional signals while the brake lights are on?