Identifying input polarity

[RalphB]

Hi'
I hope the title is reasonably accurate.
My problem.
I have a 12 volt device for a caravan but I can't identify what the polarity is, of the two wires that feed it. For info. one is white with an orange stripe, the other is brown with a green stripe.
Is there any way I can determine the polarity? I don't want to fry it. I only have a multimeter.

I've taken the thing apart, hoping I could find a capacitor or something marked with + / - and trace the circuit back to the input pins but visually it's not possible.
I've also connected my multimeter to the negative side of a capacitor and then to each of the two input pins, using the Ohms setting. One reading immediately jumps to zero, the other has some resistance showing. I want to believe that the zero reading shoes the negative polarity but I don't trust myself that much!
Any help would be very welcome.
By the way, the company that produces the device refuses to give out any information.

Ralph

 

[kpatz]

The 0 ohms between the negative side of a capacitor near the power inputs and one of the supply wires is a pretty good indication that it's the negative side, but it's hard to know with 100% certainty.

Can you post a picture of the PCB? What is the device? I assume you don't have instructions for it since they would say which wire is which.

Did you try google?

 

[Kiwi]

"By the way, the company that produces the device refuses to give out any information."
Don't you just love these sorts of companies?
Really makes you want to go out and buy more of their "quality" products.

 

[RalphB]

Thanks for your very quick response.
The device is this. https://www.alko-tech.com/uk/al-ko-trailer-control-atc
It's a very easy fitment and a good safety measure but Alko insist that only they can install it, so they refuse to help any DIY, so no instructions or help. I emailed them anyway but just silence from them.
They charge around £550 for supply and fitting. Easy money!
Mechanically, fitting is easy peasy. No adjustment of brakes etc but it's just the wiring that's confounding me.
I bought the unit from a caravan breakers on eBay and they say "normally" white wire is positive, which is not what my multimeter seems to suggest.
Re a picture. Just to confound me, my phone isn't talking to my PC so I'll need to fix it before I can post a picture.
I should have said that I've spent almost a week Googling and asking other caravan owners through caravan forums if they could help with no luck.
Because new caravans have the unit already fitted and older 'vans owners had Alko company fit them, they don't know the answer.
There are a few guys who, like me, have fitted the units themselves so i'm hoping one of them will pick up on my posts.

Ralph

 

[kpatz]

Maybe try a forum... or ask someone that had one installed to see where the wires are connected.

Nothing like saying "we only allow professional installation" so they can charge more, and then refuse to provide any information on the product to aid in installation, or troubleshooting for that matter. Corporate greed is a pet peeve of mine.

 

[dave9]

Image from: https://www.yumpu.com/en/document/read/11475815/atc-handbook-al-ko
https://www.yumpu.com/en/document/read/11475815/atc-handbook-al-ko
Edit: Here's the PDF version:
https://caravanchronicles.files.wordpress.com/2013/03/atc-handbook.pdf

Don't know if this helps, it's all I saw except some more Al-Ko here:
https://www.yumpu.com/en/document/view/11475815/atc-handbook-al-ko

 

[RalphB]

Hi Dave9,
Thanks for this but I have this manual downloaded.
There are a few documents and videos around but none are close to solving my problem.

I've uploaded photos of the board as kpatz asked.

 

[dave9]

Those are lovely pics for trying to sell an item but not great for trying to trace the circuit.

Top-down and bottom up at 90' angle, wasted space cropped out, ideally hosted on an image server so they can be high resolution.

Bottom up pic is conspicuously missing since that would be the start of tracing where the wire connector is soldered down, then you can use a multimeter between that pin and suspect grounds around the board... the caps are a good/probable place but any ICs should have a datasheet and pinout where you can see which pins are ground. Also that silver border around the PCB is probably ground.