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voltage question on trailer wiring harness

marilynmichael
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marilynmichael Member

marilynmichael

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I have a 2004 Cayenne S with factory installed towing. I have been trying to install a Sonar Step wireless back up system on the vehicle, but it fails. I plug the same one in on a friend's Toyota 4Runner and it works perfectly fine.

We measured the voltage between the ground (bottom left pin) and the reverse (center) on my electrics. Whether in reverse or not, it puts out a pulsating 18 to 24v.

On my buddies Toyota the voltage is 0 when not in reverse and 24 when in reverse.

Any ideas ?

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marilynmichael Member

marilynmichael

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I never seen 18/24V on a Cayenne with factory installed towing system, you will be mistaken.

Well, we will check it again, but are pretty sure that is what we are finding. We'll use a different voltmeter.

What should the values be?

Thank you

Michael

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wvicary Member

wvicary

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Are you measuring the output voltage from your vehicle or from the device? I know of no automotive vehicles that use over 13v output to operate accessories. Test your meter across the battery terminals to verify the meter... should read about 12.5 volts without the engine running and approx 13.5-14v running depending on loads conditions.

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  • 3 weeks later...
darrinsmith Member

darrinsmith

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Hi

My understanding was that the tow pack computer alternates the DC current (very quickly) from time to time to work out if the trailer lights are blown.

This is why you get a fluctuating current on your meter.

I guess if the current is the same both ways (ie zero) then the computer assumes the trailer lights are not working, as there would be a load differential if they were.

Have you tried tapping into the rear light wiring harness instead?

Best of luck!

DS

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