2007 Yukon Denali/Voltage between negative battery post and disconnected negative cable

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rick ediger

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Hey all. This is my very first thread post ever. I have a 2007 Yukon XL Denali with a 6.2 and 172,500 miles. It seems to have several electrical issues. 1. There is voltage (12.2v) between the negative battery post and the DISCONNECTED negative battery cable. Is this normal?? 2. I have low voltage (4.2v) on the vehicle end of the trailer brake pin in the factory installed seven round. My testing pointed to a bad brake controller, so I replaced the brake controller and the seven round on the vehicle end. Same issue. Any ideas out there on either problem?
 
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rick ediger

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The low voltage on the brake pin in the seven round is with KOEO.
 

Joseph Garcia

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Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

I cannot personally help you with your question; however, other members on this Forum that are much more knowledgeable than me will chime in.
 

Fless

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What symptoms caused the desire to test?

Couple of suggestions... disconnect the positive battery cable if you're trying to see if there is any potential between the battery negative and the disconnected negative cable. By putting the voltmeter in the circuit you are completing it and there will be voltage running through the voltmeter. You just woke up some modules when the VM was put in circuit.

For the brake test, leave the key out; the electric brake circuit is (should be) always hot and turning the key on should do nothing. Then check your brake pin voltage, but check it in reference to the 7-blade ground pin AND with a know good ground on the truck. Compare. Note that the brake controller is what varies this voltage and it won't be 12v with no complete trailer brake circuit and no brakes commanded.

You may have a bad ground in the trailer circuit. Check and clean the frame ground near the 7-blade.

You can also see if there is voltage to the 7-blade brake pin with the controller disconnected (again, testing with both grounds). Obviously there shouldn't be any. With the brake controller disconnected you can ohm the brake wire; but another better test would be to put a real load on the disconnected circuit while testing with a fused 12v source; something like a 2A bulb or the like.

I assume that you've tested the voltage (12v) to the controller, and the ability of that circuit to handle a load of at least several amps.

There's a short test procedure on this eTrailer page: https://www.etrailer.com/question-53547.html

Also check and clean body and engine grounds; these trucks are susceptible to failing grounds and that causes all sorts of electrical issues.
 
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rick ediger

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Thank you, Fless. I should have been more clear in my post. The voltage at the seven round brake pin on the vehicle side is without the trailer even being hooked up. The vehicle is isolated. I am currently tracing grounds down. there are several grounds on this vehicle. I think i am done on the top side. Now moving to the underside to find ground wires/cables.
 

Fless

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If there's a bad ground for the trailer connector that can be found easier by using the blades that have stable voltages and the ground: running lights, aux power to the trailer, etc. Good luck with finding whatever is causing you issues.
 

BG1988

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Thank you, Fless. I should have been more clear in my post. The voltage at the seven round brake pin on the vehicle side is without the trailer even being hooked up. The vehicle is isolated. I am currently tracing grounds down. there are several grounds on this vehicle. I think i am done on the top side. Now moving to the underside to find ground wires/cables.
the best place to check is the rear there is a ground wire there for the brake lights and trailer clean em up see if it fixes it driver side under the SUV all the way in the back20220412_174055.jpg
 
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Fless

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I'm not sure I ever understood what the problem was.
 

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