Rear Locker and Right Rear Turn Signal Possible short

Long time lurker, first time poster....

I'm working on diagnosing a problem with my lockers on an 09 H3T Alpha. Up until the last 4x4 trip where the truck took a serious beating, everything was fine. But along the way the rear locker stopped engaging. The Serv 4WD light came on and it would not let me engage the diff locks, just the flashing light. After shutting the motor down and restarting, the Serv 4WD message doesn't come on. I can engage the lockers, but when the rear is engaged, the right rear turn signal also comes on, both at the back of the truck, and on the dashboard. The front right turn signal still functions normally. I suspect that somewhere in the chassis the rear locker circuit and the rear turn signal are shorting, or there's a problem in the rear control module. The connections to the module are clean and dry, although the day the problem started I was playing in deep frozen puddles and on one recovery attemp I was dragged out over the ice that ripped the spare tire off the hanger and managed to wedge it above the diff, between the shocks.

My belief is either wires are rubbed through somewhere, or a the rear module has an internal short. I would really like to find a wiring diagram but I've only found the diagrams from Schwartzy for the 08 H3 Alpha. I suspect the H3T might be a bit different, as well as the Offroad version with the front lockers. I'm also curious how much can a tool like a Tech 2 monitor in those circuits.

Thanks in advance for any help.

Wow, that's a good one! I have no idea on the solution, but it's an interesting problem

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To my knowledge there is not a huge difference between the years when it comes to the body harness aside from features removed or added, so the 08 wiring doagrams are a good place to start.

I would get a meter and check for a short between the locker harness and the taillight harness at the plugs of each. That will help identify which wires exactly that are contacting each other. Since it's a T I am guessing the harness exits the cab and follows the frame rail to get to the locker and tail lights, unless it goes along inside the side of the bed? The SUV has everything go inside the cabin and the locker harness is the only related circuit that exits the body at all.

If it does go along the frame rail then I would bet that section is probably where your problem is so it should be easyish to locate.

Someone else that has a T may know more and be able to help better.

JPaul said:

To my knowledge there is not a huge difference between the years when it comes to the body harness aside from features removed or added, so the 08 wiring doagrams are a good place to start.

I would get a meter and check for a short between the locker harness and the taillight harness at the plugs of each. That will help identify which wires exactly that are contacting each other. Since it's a T I am guessing the harness exits the cab and follows the frame rail to get to the locker and tail lights, unless it goes along inside the side of the bed? The SUV has everything go inside the cabin and the locker harness is the only related circuit that exits the body at all.

If it does go along the frame rail then I would bet that section is probably where your problem is so it should be easyish to locate.

Someone else that has a T may know more and be able to help better.

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From what I see at the initial glance is there's a module in the back that's above the spare tire. It has a large harness going into it. I suspect it controls all the functions on the back like the tail lights, locker and fuel pump. I don't recall seeing that on my wagon. I pulled of the connection there expecting some water or corrosion possible causing a short, but it was immaculate. So now begins the deeper inspection, and tracing where they go.

There is no “locker module” under the truck. The module you refer to is the fuel evap purge controller. These often get destroyed by the spare tire. The SUVs have the same item but because the spare is mounted on the cargo door, they seem to hold up better. Regardless, I doubt this alone would cause the crazy turn signal issue. Service 4wd light can be caused by many things but, not an evap problem.

Obviously you’ve noticed the relationship between the turn signals and the locker. This is very bizarre but, it also should make things fairly easy to trace. Most often crazy electrical problems like this are due to a grounding issue (not positive). Definitely look for broken or missing ground straps back by the spare, since that is the most obvious place you noticed damage. Remove clean and inspect the grounds, making sure they have a good metal-on-metal connection. You can also make a temporary jumper wire from the battery’s negative post, and walk around the truck touching it to various parts on or underneath, to see if the turn signal starts working again. That’s a sure fire way to check the ground.

The lockers are fed by their own pigtails so the chance of actual wires getting cross connected like this is extremely small. A 12v positive cross connection is possible. However it is probably occurring at a plug connection that has been water-logged, rather than actual wires. All the same, trace the harness that feeds the rear lights. It could have been pinched somewhere underneath. Also I’ve seen some real strange issues like this from the trailer socket being jammed full of mud.