I'm pulling my hair out battling an electrical issue with my 2013 Boss. My only remaining option, as far as I can tell, is to replace the entire engine wiring harness. So now I'm trying to figure out what is the correct model number (or replacement) and where to source it from.

From a few threads, I thought that M-12508-M50 would work. That part is available from several vendors. I tried to purchase from Tasca, but after verifying my VIN, I was informed the actual part number is DU5Z-12A581-ZA which is no longer available. Can M-12508-M50 be used in its place?

So far my google-fu has failed to yield any conclusive answers.

Check out this thread:

I think your best bet is: DU5Z-12A581-W
To my knowledge, actual Boss harnesses are unobtanium. This part number is the '13-14 GT harness. My understanding is that the only change necessary for the Boss is to extend the purge solenoid connector (2 wires).

@stevbd found that M-12508-M50 was missing the oil level sensor connector.

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Thanks, I appreciate it. That was the thread I've been consulting. And that (DU5Z-12A581-W) is what I currently have ordered from Tasca. I'll proceed; thanks for the help

Update us on how it goes! I bought one myself but I'm planning to do mine only when necessary or when I have to replace the engine. I just wanted to make sure to get one before it goes out of stock! The GT one disappeared from inventories for a while during corona-time and for a while we thought the FRPP one was going to be the last one available.

Try ford parts giant.com. for ford harness. The other M-12508-50 is boss 302 R &S race car harness if I remember correctly. person to talk to dean martin at khor racing. Also I've had very good tech from LMR.

Oh, I definitely will. I guess I need to share my symptoms, in case it helps anyone else in the future.

I purchased the car in March of 2024, with 113k miles. On the 3 hour drive home, the gauge cluster would occasionally flash various idiot lights, and I saw the "service advancetrac" message a few times. I hadn't learned the interface yet, and it was pouring rain, so I didn't even know about being able to read voltage.

This behavior continued. If I had traction control off, it would be reset and come back on. I finally found the voltage meter, and I could observe voltage dropping to low 12v, or sometimes it would spike to 16 volts (which appears to be the max value the meter will display). Things progressively got worse. Eventually, the center stack (radio, HVAC including fans) and gauge cluster would completely shut off, brielfly, while driving. That's unnerving. When everything comes back on, it's all reset; bluetooth has to reconnect, traction and stability control come back on, etc. Fortunately, power steering and brakes continue to work, so I don't think it's a safety issue - yet.

Every time this happens, it leaves codes resident. Lots of them. I stopped pulling them long ago, so I can't remember the exact codes. But there are codes around ABS, Advancetrac, the electrical system; all kinds of stuff. It appears to be a function of electrical load; it happens frequently when the AC is on. I live in Alabama, so that's the majority of the year. Because of these problems, I generally avoid driving the Boss in the summer months. I've also experienced these symptoms after a few high rpm pulls, and it even happens during autox. That's super annoying.

Since I purchased the car, I have:

1. Replaced the alternator with a new OE Boss alternator
2. Replaced the battery
3. A year ago I had it at one local dealer, twice. The first time, the tech found a couple of pigtails with bad pins and replaced them. Things improved, temporarily. The second time around, he recommended I replace the alternator and the pcm.
4. A few weeks later, I had a local guy, strong in electrical, go over the car. He cleaned and reconnected all the ground wires, etc. Again, things improved, but issues eventually resurfaced.
5. Recently I had a different local guy check it out. He's highly trusted in my local autox club, and a ford tech. He had it hooked up to all his available diagnostic equipment, and he suggested I replace the ABS module. So I replaced it with the 302s/r unit, and that had no effect.

So at this point, I think it's gotta be the wiring harness. Sure it could be the pcm, but I'm skeptical. This place has several threads about exposed wires causing all kinds of weird issues.

t-ray said:

Oh, I definitely will. I guess I need to share my symptoms, in case it helps anyone else in the future.

I purchased the car in March of 2024, with 113k miles. On the 3 hour drive home, the gauge cluster would occasionally flash various idiot lights, and I saw the "service advancetrac" message a few times. I hadn't learned the interface yet, and it was pouring rain, so I didn't even know about being able to read voltage.

This behavior continued. If I had traction control off, it would be reset and come back on. I finally found the voltage meter, and I could observe voltage dropping to low 12v, or sometimes it would spike to 16 volts (which appears to be the max value the meter will display). Things progressively got worse. Eventually, the center stack (radio, HVAC including fans) and gauge cluster would completely shut off, brielfly, while driving. That's unnerving. When everything comes back on, it's all reset; bluetooth has to reconnect, traction and stability control come back on, etc. Fortunately, power steering and brakes continue to work, so I don't think it's a safety issue - yet.

Every time this happens, it leaves codes resident. Lots of them. I stopped pulling them long ago, so I can't remember the exact codes. But there are codes around ABS, Advancetrac, the electrical system; all kinds of stuff. It appears to be a function of electrical load; it happens frequently when the AC is on. I live in Alabama, so that's the majority of the year. Because of these problems, I generally avoid driving the Boss in the summer months. I've also experienced these symptoms after a few high rpm pulls, and it even happens during autox. That's super annoying.

Since I purchased the car, I have:

1. Replaced the alternator with a new OE Boss alternator
2. Replaced the battery
3. A year ago I had it at one local dealer, twice. The first time, the tech found a couple of pigtails with bad pins and replaced them. Things improved, temporarily. The second time around, he recommended I replace the alternator and the pcm.
4. A few weeks later, I had a local guy, strong in electrical, go over the car. He cleaned and reconnected all the ground wires, etc. Again, things improved, but issues eventually resurfaced.
5. Recently I had a different local guy check it out. He's highly trusted in my local autox club, and a ford tech. He had it hooked up to all his available diagnostic equipment, and he suggested I replace the ABS module. So I replaced it with the 302s/r unit, and that had no effect.

So at this point, I think it's gotta be the wiring harness. Sure it could be the pcm, but I'm skeptical. This place has several threads about exposed wires causing all kinds of weird issues.

Click to expand...

That stuff sounds like classic BCM issues to me... Seems like the problems are inside the cabin as opposed to in the engine bay. If it was engine harness I'd expect issues with O2 sensors and fuel injectors, that kinda thing. I would've said make sure the connector is properly seated, but it sounds like you did that. BCM COULD be bad... fortunately that's not too hard to replace. There's a little grommet under the plastic cowl hood trim piece (passenger side -- there's a driver's side one too, but if that one fills up it'll just kill your windshield wiper motor) that is meant for draining water out of the firewall. Over time it'll fill up with garbage and then water will fill up the firewall and drain down through the HEPA filter to the inside of the cabin right onto the BCM. If you check yours and the firewall has water in it, or the grommet is filled with crud, there's a pretty good chance your BCM is shot. If you find that it is your BCM, if I remember correctly all of the BCMs are the same, so you can get a used V6 one off of ebay and it'll work just fine. I retained my V6's BCM when I built my car and just reprogrammed it with FORScan and it works great.

What kinda codes are thrown?

I don't recall what the codes were. I stopped paying attention. I'll try to pull them soon.
You are the second person to suggest it could be the BCM. What does that entail? How is the part listed in the ford catalog?

t-ray said:

I don't recall what the codes were. I stopped paying attention. I'll try to pull them soon.
You are the second person to suggest it could be the BCM. What does that entail? How is the part listed in the ford catalog?

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It's the passenger side cabin fuse box. That's the body control module. Sometimes you can look at it and see visible rust on connectors if it's really bad. Sometimes you can also feel water on the floor or smell mold. Sometimes it's as simple as one of the big wire harness connectors coming loose. Triple check everything though, I'm just taking my best guess based on the info you gave -- and I'm no mechanic.

I believe this would the the Ford catalog part (BR3Z15604C -- but there are a couple variations):

Last I checked it was still possible to buy new ones, but if you can't find any there's always plenty to find on ebay or at the junkyard. Here's one from Parts Farm:

BTW -- if you have the 302S ABS module -- I believe it's normal to have the service advancetrac lights, so you can rule that one out (someone please correct me if I'm wrong). You can find more info about that in the forum.

I think if you have water issues in cabin check your a/c drain. Also heater core. Heater core you will know loosing antifreeze? Just a thought.

BackInBlack said:

BTW -- if you have the 302S ABS module -- I believe it's normal to have the service advancetrac lights, so you can rule that one out (someone please correct me if I'm wrong). You can find more info about that in the forum.

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Oh yeah, that's totally normal. The traction control light and the ebrake light are both displayed. But I've only had the abs module in for about a month; these symptoms are over two year old at this point.

And thank you for the references on the bcm.

Update - I dropped my car off for quite a bit of work. In addition to the electrical problems, I've developed an oil leak from what I suspect is the valve cover gasket on the passenger head. So I am having the valve cover gaskets replaced and well seals plugged, and new timing chains & tensioners.

At the same time, I am replacing the alternator *again*, the full wiring harness, and also replacing the pcm, all in one go. If the electrical problems persist after all this, I'll just have to accept that the car has electrical gremlins. If that happens, I've already told my partner I'm pulling out the stereo & hvac and might as well go full track car.

I finally have the car back. New alternator, a refurbished pcm, and engine harness all went in. At the same time, I had the valve cover gaskets replaced, along with new timing bits (tensioners, chain, cam sprockets). I didn't get a chance to drive it very much this weekend, but I did drive it in the heat with the AC on full blast and the voltage was steady >= 13.5 <= 14.0. I don't completely trust it yet, but this is the best hope I've had yet.

And despite literal hours of research, it appears either I ordered the wrong wiring harness, or received the wrong harness. The plug for the evap system isn't currently connected, and needs to be extended ... 18 inches? 24 inches? Not quire sure. Electrical is *not* my thing. But for now I'm just driving without it connected.

So now the dash is all lit up - ABS (because I went with the 302 s/r abs module), tire pressure (my tpms sensors aren't registered correctly), CEL (I have DTC codes for the abs and evap modules), and the emergency brake light. I think there's something else I'm forgetting lol

t-ray said:

I finally have the car back. New alternator, a refurbished pcm, and engine harness all went in. At the same time, I had the valve cover gaskets replaced, along with new timing bits (tensioners, chain, cam sprockets). I didn't get a chance to drive it very much this weekend, but I did drive it in the heat with the AC on full blast and the voltage was steady >= 13.5 <= 14.0. I don't completely trust it yet, but this is the best hope I've had yet.

And despite literal hours of research, it appears either I ordered the wrong wiring harness, or received the wrong harness. The plug for the evap system isn't currently connected, and needs to be extended ... 18 inches? 24 inches? Not quire sure. Electrical is *not* my thing. But for now I'm just driving without it connected.

So now the dash is all lit up - ABS (because I went with the 302 s/r abs module), tire pressure (my tpms sensors aren't registered correctly), CEL (I have DTC codes for the abs and evap modules), and the emergency brake light. I think there's something else I'm forgetting lol

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If you're using the Boss manifold and the wiring harness is GT, I think it needs to be extended about 40 inches from what I remember. Regarding the purge solenoid, I think it'll run fine aside from the code so long as everything is hooked up properly (and the purge valve isn't stuck open -- in which case you might have a vacuum leak/high fuel trims. you can always cap it off if you want to be sure). Hope everything works! Where'd ya get the PCM from? Used? Rebuilt?

Thanks man, I appreciate it. I got the pcm from a place named Flagship One; refurbished (and reprogrammed).

Going back to the beginning of my own thread, you already told me the purge solenoid connector would need to need to be extended. I had totally gotten - a lot has happened in the past 4 months.

Regardless, i can finally drive this car. I've had it since March of 2024 and haven't driven it more than 2 hours from my house because I was worried about a massive tow bill. Now my partner and I can finally take our cars up to the dragon.

t-ray said:

Thanks man, I appreciate it. I got the pcm from a place named Flagship One; refurbished (and reprogrammed).

Going back to the beginning of my own thread, you already told me the purge solenoid connector would need to need to be extended. I had totally gotten - a lot has happened in the past 4 months.

Regardless, i can finally drive this car. I've had it since March of 2024 and haven't driven it more than 2 hours from my house because I was worried about a massive tow bill. Now my partner and I can finally take our cars up to the dragon.

Click to expand...

I've had Flagship One on my radar. Sure I'll have to do the same one day. Did you refurbish your original PCM or buy one from them? If you bought one, does it look the same? Like it uses the same housing, etc?

I hate to say it but I didn't even open the box. It was shipped and sat in a closet until my friend could fit me in his schedule. I *assume* it uses the same housing; my friend kept me informed throughout the process (and other work he's done in the past), and he didn't mention anything about the pcm. And I purchased a unit from them. My pcm is still in a box. If I ship it to them I will get store credit, but I have no idea what I'd use it for.

I will say that as a vendor they kept me informed; I received emails when the pcm was put onto the bench for programming, when it was going through testing (apparently they do a multi day soak test of some sort). My initial order was delayed because they didn't receive the correct pcm from *their* source apparently. Overall it took almost a month between ordering and it arriving at my door. I wasn't in a rush so it wasn't a problem, but you should keep that in mind if you decide to order one.