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Flickering Head Lights... ARGHH

20
26
Exp. Type
Time Attack
Exp. Level
20+ Years
Utah
Flickering Head Lights... ARGHH
Ford Dealerships in UTAH have failed me for over a year now. I need ideas guys I have traced everything I can. Ford thinks it may be the BCM module but I am not convinced, they have one on order for a year now. they have changed the alternator, and starter motor.

Symptoms read close:
This only happens when the motor is on! when the motor is off the lights, DO NOT FLICKER. I do not think there are any problems with the lights themselves. Also, in auto or lights on the same effect, they blink after a moment of motor running inconsistently.

Behaves inconsistently sometimes it's fine but usually not. I think I have a bad ground somewhere but cannot find it.

video below:

BLINKING LIGHTS
 
1,124
1,093
In the V6L
Flickering Head Lights... ARGHH
Ford Dealerships in UTAH have failed me for over a year now. I need ideas guys I have traced everything I can. Ford thinks it may be the BCM module but I am not convinced, they have one on order for a year now. they have changed the alternator, and starter motor.

Symptoms read close:
This only happens when the motor is on! when the motor is off the lights, DO NOT FLICKER. I do not think there are any problems with the lights themselves. Also, in auto or lights on the same effect, they blink after a moment of motor running inconsistently.

Behaves inconsistently sometimes it's fine but usually not. I think I have a bad ground somewhere but cannot find it.

video below:

BLINKING LIGHTS
I've looked at the wiring diagrams for the headlights (HID without leveling) and it's pretty straightforward. There's a low-beam signal and a high-beam signal from the BCM and what I see in the video is the right low beam flickering on and off when the engine is running. Does it do it with the lights on high beam as well? If no, then it's probably the BCM or a connector problem on the "low-beam on" signal between the BCM and the headlight itself. If yes, then the BCM is probably fine and it's something else, like maybe fuse F35. F35 is in the big fusebox beside the engine, and it supplies power to the right headlight assembly. If that fuse is flakey - vibration from the running engine bothers it, perhaps - then replacing it might help. Or not. If you don't have a spare fuse lying around, swap it with F33, which supplies power to the left headlight.

One caveat - I have the diagrams etc for 2016's - Ford may have changed some stuff for 2020, but this kind of thing tends to be the same for a long time. That said, I just checked the 2020 Mustang Owners Manual and it lists those two fuses as the power supply for the headlights on the GT350 and GT500.

1664751779776.png
 
20
26
Exp. Type
Time Attack
Exp. Level
20+ Years
Utah
Oh, thank you for the excellent response. So the high beams do blink as well in the same sequence as the low beams when the motor is running. So I have a service manual cd but have not been able to get good details like you out of it for diagrams, I think I purchased a bad one. you seem to have a better fuse diagram or more accurate as well. I will check those fuses when I get home from work. Fingers crossed
 
49
60
Exp. Type
Time Attack
Exp. Level
Under 3 Years
So cal
why not hook a test light up to the power for the headlights and see if it flickers as well, that will eliminate if its a bad ground for the headlight or if in fact the bcm is sending out a flickering power signal. Or just run a separate ground test wire directly from the battery to the headlights.
 
20
26
Exp. Type
Time Attack
Exp. Level
20+ Years
Utah
why not hook a test light up to the power for the headlights and see if it flickers as well, that will eliminate if its a bad ground for the headlight or if in fact the bcm is sending out a flickering power signal. Or just run a separate ground test wire directly from the battery to the headlights.
yeah not entirely sure how to find the source from the bcm but I like the idea. I will have to purchase a test light don't have one atm
 
1,124
1,093
In the V6L
Here's the right headlight wiring. The "SIGNAL" wire on the far left comes from fuse F68 in the same fuse box as 33 and 35. There is no connector for it at the fuse box - it's hard wired into the box itself. The only connector is the one at the headlight. If you want to troubleshoot the wiring at the headlight connector C1041, the pin-out is below. I expect all the signals are on-off so a test light with a pointy prod would probably be all you need.

As for the grounds, it's worth checking, but again, there are no connectors in line, so it's doubtful. That said, the diagram at the bottom of the page shows where it is - looks like down under the windshield washer bottle, perhaps.

Happy hunting!

1664899619562.png

1664900006401.png1664900300844.png
 
20
26
Exp. Type
Time Attack
Exp. Level
20+ Years
Utah
Here's the right headlight wiring. The "SIGNAL" wire on the far left comes from fuse F68 in the same fuse box as 33 and 35. There is no connector for it at the fuse box - it's hard wired into the box itself. The only connector is the one at the headlight. If you want to troubleshoot the wiring at the headlight connector C1041, the pin-out is below. I expect all the signals are on-off so a test light with a pointy prod would probably be all you need.

As for the grounds, it's worth checking, but again, there are no connectors in line, so it's doubtful. That said, the diagram at the bottom of the page shows where it is - looks like down under the windshield washer bottle, perhaps.

Happy hunting!

View attachment 79957

View attachment 79958View attachment 79959
awesome details, thanks I will review this tonight! I really appreciate the details
 

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