Towbar Information

[glenc]

Thanks Maverick

[Umai Naa!!]

The car conducts a bulb out test when the car is started and to do this it puts some juice through the bulbs. The electric brakes are seeing this as brake light activity and turning on the electric brakes. You should be able to get around this using a few diodes. Of course I could be wrong but I understand that electric brakes run off the brake light circuit?

Yes, and no. Depends how it's been wired up. I've been wiring them up off the brake pedal switch on the master cylinder, which is before any control module intervention. This seems to be the most effective method.

[Von Richthofen]

G'day Folks,

I'm not a passat owner but have just been through the trailer light issue with my '07 Jetta and thought my experience may be helpful.

I had just changed my boat trailer lights over to LED's. Connected the car & got the strobing issue. This is a result of the LED's being lower (see correction posted by tryingaVW below) resistance than the incandescent globes & the globe out detection system continually checking for resistance which would indicate that the globes were OK.

Negotiated a price with my local dealer for the VW LED Load simulator (Part No. VGA0055204 LOAD LED LOAD SIMULATOR 5A-300708RA) fitted the load simulator & all trailer lights working OK..... except for "LH trailer light out" warning via the MFD.

As indicated elsewhere in this thread the Australian standard for trailer wiring makes the tail lights common ie both lights fed from the RH tail light circuit form the car. Whereas the European standard is for an independent circuit for each tail light.

In earlier model VW's (including my '07 Jetta) there were only 2 options in the trailer light controller (North America & Rest of the World). VW have since developed additional codes for other countries, including Australia. The code for Australia basically stops the globe out detection system from looking for the LH trailer light circuit.

Even though the code for Australia does not appear on earlier model trailer light controllers the code (03) can still be entered into the system & it will work properly. This will solve the LH light out warning on the MFD.

My local dealer Wakeling fixed it for me in 15 mins while I waited & washed the car before giving it back to me...... No charge, as they treated it as a warranty issue.

Now for the LED load simulator..... I have pulled mine apart and checked out the components. It is made up of a number of 15W resistors that are wired in parallel with the trailers LED circuits. This effectively decreases (corrected 30/7) the load seen by the car without effecting the voltage across & current flow through the LED's

I have checked out the components & you would get change from $50.

I intend to make one up & permanently to mount on my trailer & will keep the VW model in the boot in case I get caught out & need to tow a trailer with LED's.

Regards, The Von.

[Swallowtail]

Thanks The Von... I found that exact same setting by fluke and resolved it myslef a long time ago. Good to know that is the correct way to fix it though! The local dealer had no ideas.

[Umai Naa!!]

Back in the early days when these issues were becoming apparent, VW said at that stage there was no support for LED trailer lights. They had then since released the load simulators, along with necessary coding alterations. This was all fine and dandy, and it worked well, but it was not widely known. Hence, why some dealers have been able to solve the problem (admittedly, Wakeling's have a gun VW foreman/technician there), and others haven't.

[tryingavw]

This is a result of the LED's being much lower resistance than the incandescent globes & the globe out detection system continually checking for resistance which would indicate that the globes were OK.
Regards, The Von.

minor correction : actually the LED lights have a higher resistance and do not draw enough current for the to see a correct load of approx 1Amp.

for the sake of completeness Von can you advise what resistance reading was marked on the resistors? i estimate it would be 1 Ohm. the Watt reading relates to the power the resistors can handle.

a normal trailer light is 15W ( and resistance of say 0.8 ohms) and would draw about 1 amp whereas the LED might be say 2W with a higher resistance of say 70 ohms and draw only 20 milliamps ( 0.02 A) .

[Von Richthofen]

Hmmm...... got me thinking now.

An individual LED if connected in forward polarity will present as a very low resistance (basically a switch) once the threshold voltage of 0.6 volts is reached. However, you are right, in a light array where the LED’s are connected in series there will be a resistor of some value also connected in series to limit the current flow through the LED’s. I’m not sure what the value of this resistor is in the case of the trailer light circuit. Also, the load simulator being connected in parallel is reducing the total resistance of the combined circuit that the car is seeing but I'm not sure to what value.

When I get the chance I’ll connect the trailer to a battery without the LED load simulator & measure the current so that I can calculate the resistive values of the individual circuits.

In the example you gave above of a 15w globe at 12 volts, the resistance of the globe will be 9.6 ohms & draw 1.25 Amps. Assuming my maths & memory of Ohm's law is correct.

In the mean time here are the resistance values in the LED load simulator.......remember these are connected in parallel with the individual trailer circuits:
Brake Light = 68 ohms
Turn Signals = 39 ohms each
Tail Lights (common circuit) = 2 x 33 ohms (in parallel) ie effectively 16.5 ohms

The actual resistors are Arcol brand, wire wound & the series is HS15 (the 15 designating 15 watts)

Once I measure the current in the LED circuits on my trailer, I’ll include the LED circuit resistances to the thread and determine exactly how much the load simulator is reducing the overall resistance of each circuit.

Regards....

[tryingavw]

you are correct, my maths was wrong. oooops.

FYI LED forward voltages are much higher than a diode- different colors vary- but about 2.5-3.5V when operating.

also the power rating can be worked out by v2/R. so brakes= 14*14/68 = 3W, so them using 15W resistors is very conservative, turn =5W . and the tail lights = 11.5Watts.

As it should always be with da Chermans. ( or the blockheads as i affectionately call them )

Best place to buy resistors is probably altronics online. Altronics - Your One Stop Audio Visual & Electronics Supplier.

Hmmm...... got me thinking now.

An individual LED if connected in forward polarity will present as a very low resistance (basically a switch) once the threshold voltage of 0.6 volts is reached. However, you are right, in a light array where the LED’s are connected in series there will be a resistor of some value also connected in series to limit the current flow through the LED’s. I’m not sure what the value of this resistor is in the case of the trailer light circuit. Also, the load simulator being connected in parallel is reducing the total resistance of the combined circuit that the car is seeing but I'm not sure to what value.

When I get the chance I’ll connect the trailer to a battery without the LED load simulator & measure the current so that I can calculate the resistive values of the individual circuits.

In the example you gave above of a 15w globe at 12 volts, the resistance of the globe will be 9.6 ohms & draw 1.25 Amps. Assuming my maths & memory of Ohm's law is correct.

In the mean time here are the resistance values in the LED load simulator.......remember these are connected in parallel with the individual trailer circuits:
Brake Light = 68 ohms
Turn Signals = 39 ohms each
Tail Lights (common circuit) = 2 x 33 ohms (in parallel) ie effectively 16.5 ohms

The actual resistors are Arcol brand, wire wound & the series is HS15 (the 15 designating 15 watts)

Once I measure the current in the LED circuits on my trailer, I’ll include the LED circuit resistances to the thread and determine exactly how much the load simulator is reducing the overall resistance of each circuit.

Regards....

[Von Richthofen]

Eventually got the chance to measure the voltage across & current flow through the LED trailer light circuits so that I could calculate the resistance value.

Circuit V, I (mA), Ω, Load Simulator Ω, Total Circuit Ω, I (mA)@ 12 v
LH Signal 12.9, 195, 66, 39, 24.5, 489
RH Signal 12.9, 193, 67, 39, 24.6, 487
Tail Lights 13.02, 46, 283, 16.5, 15.6, 770
Stop Lights 12.9, 197, 65, 68, 33.4, 360

Sorry about the formatting could cut & paste from excel successfully.

The LED load simulator is reducing the overall resistance by being inserted in parallel with LED trailer light circuits & therefore increasing the current flow through the combined circuit.

This reduced resistance & resultant increased current is obviously what is required to satisfy the VW can bus / globe test system and stop the trailer lights from strobing.

Regards, Von

[dammfool]

Does anyone know the size of the bolt that screws into the towbar to keep it tight