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Another track day, another failure

JDee

Ancient Racer
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W2W Racing
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halfway between Mosport and Shannonville
So the fixes for the smoking engine worked, new GT350 drivers side valve cover and a catch can for added safety, catch can stayed dry and no smoking. Win! Car ran great and it laid down a collection of 1.33s and 1.34s at Mosport. Will be moving up to Open class at the next track day by the looks of things now.
But...in the last session of the day got another black flag, came in and I had no rear lights at all. No brakes, no turn signals, no running lights.
Haven't had a chance to look at anything yet but it just seems odd that those things that are likely 3 separate circuits would all die at once. Makes me think it is more likely a wiring harness failure? Hopefully something simple like a junction plug came loose?
Anyone ever have anything like that happen before or thoughts on where the problem may be?
 
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3,198
connect all the wiring plugs back together and check for corrosion while you're doing it. then tie wrap them together so they won't come loose.
While I feel bad about the black flag, remember that you're running times there faster than the Trans Am car of the 60s and still have A/C and cruise control.
 

JDee

Ancient Racer
1,216
1,082
Exp. Type
W2W Racing
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20+ Years
halfway between Mosport and Shannonville
OK will do that, thanks. No A/C anymore, but the cruise still works!:D

Checked all the plugs in the back they seem secure and plugged in.
Running lights are working.
The brake lights don't work except the high 3rd light does come on.
The turn signals are making a weird pattern, not flashing on/off but doing some funky beat thing?
Attaching a video of the sound the turn signals are making, perhaps that means something?


So I am suspecting the turn signal flasher has something to do with this? Does that make any sense?
 
3,446
3,198
by any chance are you running LEDs? because LEDs installed where bulbs use dto go, or in conjunction with front turn signal bulbs can fake out the new style flashers and cause all kinds of weirdness.
 
Check that pin 6 on the tail light connectors - either side, they're the same - is connected to ground. It's the ground connection for the brake lights, tail lights, turn signals and four-ways. If that's not grounded, nothing will work back there. The actual ground connection to the chassis is "G400" as shown below

The tail light connectors are C498 and C499.

1626804563741.png

This is the pinout for the C498/499 connectors.

1626804718216.png

Here's the wiring diagram - as you can see, if G400 isn't actually connected, both sides of the tail light assemblies will fail.

1626804876140.png
 

JDee

Ancient Racer
1,216
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Exp. Type
W2W Racing
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20+ Years
halfway between Mosport and Shannonville
@JAJ
Thanks for those diagrams, much appreciated. G400 is for sure connected, I was looking for grounds and saw it right away, there are 3 small black wires on that connector. All the wiring is neat and tidy and in place, it's all very clean and neat, I try to keep my shiznit pretty clean.
I've since done two things.

First took it to a friend's garage where I get work done that I can't/won't do and he put their diagnostic tool (Snap-On, not a Ford one) on it to see what was going on. There were a lot of old codes in there but he was able to get a current snapshot. His tool said the BCM module is not communicating , he checked all the fuses and relays in both boxes and they all seem to be OK so there's nothing more he could do. He said I'm going to have to take it to a Ford stealer, er, dealer, and get them to do whatever they need to do to get that BCM module talking again. This is a hassle as there's no Ford dealer where I live so it's a trip. He said it would likely only take an hour or two for the dealer guy to get that BCM module up and running again. Does that sound right?

Secondly, I tried to actually check the light bulbs. How in the name of God do you get at the light bulbs in the rear lights? There's a nice little twisty thing to unscrew on the back of the light unit, but when you take that off there's another bundle of wires going down into the bowels of the tailight assembly to presumably a light bulb in there, somewhere. I wrecked one of the rear lights trying to open it up, I guess they're not openable, I just tore some trim off so still good enough for a track car, but no way I can figure out how in hell to do a simple thing like look at a lightbulb. Surely you don't have to buy an entire tail light unit if a bulb goes out? Up front it looks like the front bumper has to come off to get at the front ones I think, or maybe I can get at it with the inner fender cover pulled out of the way, can't remember. Not user friendly stuff though. It is quite possible the left front turn signal light is out as it got damaged during a loading incident, but I haven't had a chance to get a look there yet, ran out of time due to wasting too much time on the rear.

Thirdly, another guy I know who does wrenching for a living called a Ford guy he knows, and Ford guy said that only one light bulb in the turn signals being blown can bring that whole system down as I am experiencing. Is that for real?

This is not encouraging stuff, getting kind of tired of seemingly simple things turning out to be a dog's breakfast to fix.
 
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Hmmm... I don't have a lot of information about how the BCM works, although I'm surprised that the car will even start if the BCM's not communicating. The BCM is the hub that runs everything else - it gets a signal from the ignition key and sends a signal to the ECU to start the engine, for instance.

If you haven't tried it yet, how about disconnecting the battery for about an hour and letting everything discharge. It might get the BCM back to working - it's one of the modules in the car that's "always on" and it might have gotten into a mode it can't recover from, so like the famous Microsoft three-finger salute, reboot it and see if it helps.
 

JDee

Ancient Racer
1,216
1,082
Exp. Type
W2W Racing
Exp. Level
20+ Years
halfway between Mosport and Shannonville
Hmmm... I don't have a lot of information about how the BCM works, although I'm surprised that the car will even start if the BCM's not communicating. The BCM is the hub that runs everything else - it gets a signal from the ignition key and sends a signal to the ECU to start the engine, for instance.

If you haven't tried it yet, how about disconnecting the battery for about an hour and letting everything discharge. It might get the BCM back to working - it's one of the modules in the car that's "always on" and it might have gotten into a mode it can't recover from, so like the famous Microsoft three-finger salute, reboot it and see if it helps.
OK thanks. I've done the auto equivalent of the 3 finger salute a couple times, but just a disconnect/reconnect. I'll take it off and leave it overnight and see what happens. Will try to push buttons and stuff to try to make sure there's no stored energy hiding somewhere.
Weird thing is stuff seems to be generally working OK, motor starts and runs fine, just the brake light/turn signal circuit seems to be dead.
 
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sfo
@JAJ

Thirdly, another guy I know who does wrenching for a living called a Ford guy he knows, and Ford guy said that only one light bulb in the turn signals being blown can bring that whole system down as I am experiencing. Is that for real?
I do not know if that is true but based on my own wrenching on the S550 that sounds exactly like the quality of Ford engineering. How you figure it out. Good Luck!
 

JDee

Ancient Racer
1,216
1,082
Exp. Type
W2W Racing
Exp. Level
20+ Years
halfway between Mosport and Shannonville
So I did a 12 hour disconnect on the battery, no change. Car is going to the Ford dealer up the road in the next town on Monday the 26th. They want it left for the day, hope that's not a bad sign.....the upside is that the service writer told me they have a particular guy who does this stuff and that was why I had to wait to the 26th, hopefully he knows his shti.
Still have that Ford Racing PP2 tune in there, hope that doesn't interfere with what they have to do.
 
So I did a 12 hour disconnect on the battery, no change. Car is going to the Ford dealer up the road in the next town on Monday the 26th. They want it left for the day, hope that's not a bad sign.....the upside is that the service writer told me they have a particular guy who does this stuff and that was why I had to wait to the 26th, hopefully he knows his shti.
Still have that Ford Racing PP2 tune in there, hope that doesn't interfere with what they have to do.
That's disappointing. That said, it occurred to me to look up the G400 ground point and see how many wires it has - the answer is 7, so the one you found with 3 isn't G400. Here's the diagram:

1626900187631.png
BTW, these diagrams are from the 2016 Mustang Service Manual, so they should match up with the way your car is wired.

If any or all of the other stuff connected to G400 still works, then it's not likely the culprit.
 

carver

breaker of wrenches
333
428
ontario
Check grounds first, always. Then move to the hot side. When more than one item is acting up, grounds are a likely common place to find the problem.
Hey JDee I feel your pain! Totally agree with the ground as a possible culprit. My Focus RS was a new car and had grounding issues. When I removed some of the various ground wire connections I realized that the paint was covering most holes and the contact for the connectors was minimal at best.You would think that the screw or bolt through the metal would be sufficiant but it's worth a look I think. I did some paint sanding around the holes on the body and the connectors that had been painted as well. Problem solved.
Good luck with it.
 

JDee

Ancient Racer
1,216
1,082
Exp. Type
W2W Racing
Exp. Level
20+ Years
halfway between Mosport and Shannonville
Thanks Dave. Grounds look good, bright shiny metal under them. Problem for sure is the BCM (Body Control Module) has shut down, not communicating at all with other modules and apparently only the dealer has the equipment to get it back to talking with the rest of the network. Anything to do with the brake light circuit runs through the BCM, so turn signals and 4 way flashers are also out. Running lights work but that's all.

*RANT* I'm not a luddite, spent the last 15 years of my working life in the high tech field dealing with everything from wonky desktop computers to crapped out WANs and server farms, but I can see no reason why a simple on/off switch has to be run through a series of interconnected "modules" which actually seem to be micro computers that talk to each other and apparently can be just as flaky. This just seems like "we do it because we can" taken to the extreme. And the idea that a dead signal light can cause this whole chain of events is obscene. I should sell this thing and buy a simple, stripped down vintage race car, it would be so much easier to maintain....*END RANT*

So, I'm loading the car up on the trailer on the 26th and off to see the dealer, what a royal PITA.
 

carver

breaker of wrenches
333
428
ontario
The only diagnostic tool you needed ....back in the day , Hahahah. I feel the same way about the simplicity. My old Rotary Mazda's were indestructible. You couldn't blow one of those up if you tried ! and dirt simple to work on.



1626958908311.png
 
Really can't imagine how frustrating this is JDee, especially given that like you say there's no GOOD reason that the tail lights and turn signals need to be on the CanBus. What just so the BCM can flash the tail lights at me when I unlock the car? Given the problems that can stem from it? Ugh. Hope its not too bad.

Also frustrating that Ford charges so much for IDS which is what's needed in most cases to fix problems like this.
 

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