Thread: Towing Electrics - Big Tick

Originally Posted by discotwinturbo

I purchased a couple of these resistors and wired one in parallel on two trailers driver side indicator......and to date none have worked. Have checked, and rechecked, left it for a month or so, then tried again....yet still I cannot get the resistor to cause the trailer lights to work.

Pulse buster works fine.

I must be doing something wrong.

And I do all my own wiring on all of my cars, always working well.....but this has got me beat.

Brett.....

Pulsebuster is not doing all its supposed to as a resistor should not be needed as well unless your vehicle is like mine whereby the resistance of some trailer globes is too high to trigger the indicator.

Originally Posted by discotwinturbo

Okay. So cut the indicator cable on the trailer and place resistor in series ?

Brett....

Got it in one. Make sure it is in series.

But, as Graeme said, you shouldn't need the Pulsebuster and the resistor, unless you have something quirky.

Originally Posted by Basil135

Might be your problem, right there.

On mine, the leads from the resistor make the only connection for the RHS indicator circuit. So, from the plug, into the box, and then to the socket, that the trailer plug goes into.

Remember, electricity is lazy. It takes the path of least resistance, and so, if you have it in parallel, the resistor isn't doing anything.

Interesting Basil, all other solutions talk of presenting a lower resistance to the cars circuitry which involves placing a resistor in parallel. LEDs present far greater resistance than the resistor (globe) which is why the issue exists. If wired in parallel, the resistor will allow the correct(increased) current flow on the indicator circuit to enable the cars systems to detect the presence of the trailer. Wiring them in series would not achieve anything I believe.

I would say that Brett is on the right track with the approach he is taking, there must be some other issue.

Originally Posted by SBD4

Interesting Basil, all other solutions talk of presenting a lower resistance to the cars circuitry which involves placing a resistor in parallel. LEDs present far greater resistance than the resistor (globe) which is why the issue exists. If wired in parallel, the resistor will allow the correct(increased) current flow on the indicator circuit to enable the cars systems to detect the presence of the trailer. Wiring them in series would not achieve anything I believe.

I would say that Brett is on the right track with the approach he is taking, there must be some other issue.

The way I understood it, was that the LED's were not drawing enough for the car to detect a trailer was connected.

By placing the resistor in series, the current draw is increased, which is why it gets hot, and hence, the car see's the trailer connected.

Just had a thought. I have built my box with the resistor in series with the indicator circuit, so that there is no option for the current, but to flow thru the resistor. When people are talking about connecting it in parallel, are they taking one side of the resistor lead to earth, and the other to the active side of the LED? The way I read the original post, I understood it as being in parallel to the indicator wiring, essentially running alongside the normal wire. Which is why it wouldn't be doing anything. Just wondering if this is where the difference is?

Originally Posted by Basil135

The way I understood it, was that the LED's were not drawing enough for the car to detect a trailer was connected.

By placing the resistor in series, the current draw is increased, which is why it gets hot, and hence, the car see's the trailer connected.

Just had a thought. I have built my box with the resistor in series with the indicator circuit, so that there is no option for the current, but to flow thru the resistor. When people are talking about connecting it in parallel, are they taking one side of the resistor lead to earth, and the other to the active side of the LED? The way I read the original post, I understood it as being in parallel to the indicator wiring, essentially running alongside the normal wire. Which is why it wouldn't be doing anything. Just wondering if this is where the difference is?

Basil, it is opposite to your understanding. Your understanding of series and parallel is correct though your understanding of the difference between the two is incorrect. Resistance in series will reduce current flow but in parallel will increase current flow.

Here's a video that provides an analogy using toll booths to explain parallel and series circuits (I hope I don't come across as being condescending):

[ame=http://www.youtube.com/watch?v=pqCI6liUaME]Series and Parallel Circuits (Tollbooth Analogy) - YouTube[/ame]

Originally Posted by Graeme

Pulsebuster is not doing all its supposed to as a resistor should not be needed as well unless your vehicle is like mine whereby the resistance of some trailer globes is too high to trigger the indicator.

Hi Graeme,

Pulse buster works fine.

I have the same issue on my Touareg so was trying to avoid using my temporary pulse buster that I carry around for it....Disco is hard wired.

But I turned the Disco pulse buster off and then tried the two trailers with the resistor in parallel on the drivers side indicator cable at the rear of the mounted trailer lights and trailer lights don't work....just faint blinking.

The same method is supposed to work with the Touareg but no joy. Both resistors are the narva 12/24 volt ones

So I am doing some thing wrong.....unless I have two failed resistors from the pack which would be unlikely.

Brett...

Originally Posted by discotwinturbo

Hi Graeme,

Pulse buster works fine.

I have the same issue on my Touareg so was trying to avoid using my temporary pulse buster that I carry around for it....Disco is hard wired.

But I turned the Disco pulse buster off and then tried the two trailers with the resistor in parallel on the drivers side indicator cable at the rear of the mounted trailer lights and trailer lights don't work....just faint blinking.

The same method is supposed to work with the Touareg but no joy. Both resistors are the narva 12/24 volt ones

So I am doing some thing wrong.....unless I have two failed resistors from the pack which would be unlikely.

Brett...

Brett how many Ohms are your resistors?

Originally Posted by SBD4

Brett how many Ohms are your resistors?

Sean, it's a 21watt led load resistor...don't know the ohms though.

I just saw a pic online showing one side of the resistor on the power going into the lamp, and the other side of the resistor going to the earth wire on the lamp.

I have a wire from resistor diverted off the current line into the lamp, 10cm from the lamp, then the other side of the resistor going back into the current line, 5cm from the lamp.

I think my parallel is in the wrong spot ?

Thanks for your help

Brett...