Sorry if this has already been discussed - if it has, can someone share the link?

2009 F150 XLT 4x4 with 190,000 miles
So, I've got the 5.4 Triton and the 6r80 transmission - the neutral safety switch is inside the tranny case. Mechanic said it'd be about 3K to pull apart and swap out the sensor. The issue is that my reverse lights don't turn on when in reverse. The mechanic said that the sensor in this truck uses a magnet to break the circuit (???) or connect the circuit (???) but that what's most likely happening is that there are grindings and metal shavings from the transmission that have gotten attached to the metalic sensor so it doesn't realize it's in reverse.

I'm wondering if I wire up a new set of lights and install them on the back bumper, would that work? It seems like a lot cheaper alternative than the $3k. My question, once I find the reverse wire and run it to a switch, will it work? Or will the sensor in the transmission throw a wrench in this plan since it will always think that the switch is always touching metal?

 

Maybe try another mechanic.
A quick check shows the neutral safety switch on the outside of the transmission where the linkage is attached.
I could be wrong, but if that switch is failing, at some point you probably won't be able to start the truck.
oops my bad, that is part of the lead frame it looks like.

 

If it is supposedly in the guts of the trans you could find that particular wire coming out of the bulkhead connector and run switched power of proper voltage from somwhere else to that wire at that point. Like Newbie 5 points out you may later run into trouble if you don't either fix it or add a switched power source externally so all the electronic components know the trans is in Rev. Be sure and cut the wire coming out if you do this. You don't want to back feed voltage in to where it is supposed to be coming out from.

 

The mechanic was more right than one might think, he just explained it poorly.

There's no such thing as a "neutral safety switch" anymore, that function was moved to other components a long time ago.

The 6R80 has the internal infamous leadframe that includes the electronic detection of the shift lever position using a set of hall effect sensors read by an internal microprocessor. This information is then sent to the PCM as a digital message. The PCM decodes the message and decides what to do with it. In the case of when reverse is selected, it sends another to the BCM to turn on the backup lights, among whatever else its programming tells it to.

 

And $3k for a leadframe replacement makes dealers sound reasonable. Did he actually check the rest of the circuit? I'm assuming your average scan tool should be able to operate the lights to prove whether the BCM-to-bulbs is working. And then a half-trained tech should be able to figure out whether a wire is broken.

 

Here are the two drawings for 2009 reverse lamp circuit from transmission.
It looks like this circuit is stand alone in that it has it's own relay in the battery junction box. This relay solenoid gets it's signal from a separate set of wires out of the 6R80 transmission.
Like Spiky is saying you should check all wiring first to make sure you're capable of getting communication to the Battery Junction Box relay or not. You won't even have to crawl under there unless you want to chase down a bad wire.
You can wire up and put in a toggle switch in the cab to activate this relay in the BJB and just switch the lights on when you need them.
Of course you don't want to forget them or you could get pulled over by the cops.
You lucked out in one regard that like ProjectSHO89 pointed out, later models get a little more complicated. In fact looking at my own 2013 it appears the reverse signals comes to the BCM over CAN network.
This is a wild a** guess but I'm suspecting reverse has its own switch in early 6R80s that makes this work-around possible.
Although a mechanical relay solenoid can be wired either way it's advisable to go by the drawings and wire it like it shows there.

 

flyswat446,

Good catch! I didn't dig deep enough this morning. Thanks for filling in more details for this one.

PS89