I am dealing with my son's 99 mustang, 5 speed, 3.8L. I noticed about a month ago while he home on leave that his brake lights were not working, even the third brake is out. Everything else works. I have read probably every thread in here and other sights at least twice pertaining to brake light problems but none seem to match it. I have checked all fuses and light bulbs, changed the multifunction switch, and made sure the brake light switch at the pedal is working. I have tried to run a bypass wire from the brake light. This works except now the third brake light flashes when I turn the left signal on and the brake light overrides the turn signal if I use them while the signal is on. I'm usually pretty good at rigging things up to get them to work but this one has got me stumped and it doesn't look like I am going to be able to rig it this time. Has anyone ever encountered this? I would be really grateful to anyone who could help with this. Thanks.
No Brake Lights
- Thread starter jean-paul brown
- Start date
wmburns
SN Certified Technician
What is important about the symptom is that the 3rd high might brake light does not work. Or course this assumes that the trunk ground has been confirmed GOOD. The fact the 3rd brake light does not work usually means the multi-function switch is not the cause. Why? Because the 3rd brake light does not go through the multi-function switch.
Need to know IF fuse F2.41 has power going in/out with the break pedal depressed. The results of this test will determine the trouble shooting direction.
If no power then test the break pedal switch. Confirm power into the switch.
If power then more wiring tests needed. IE suspect a break in the wiring harness as the wire path should be good straight from the fuse to the high mounted brake light.
Again it's vital that the trunk grounds be confirm good or a huge wild goose chase could be in your future.
1999-2004 MY fuse panel schedule:
http://www.allfordmustangs.com/foru...r-swap-wont-fire-please-help.html#post2669271
Need to know IF fuse F2.41 has power going in/out with the break pedal depressed. The results of this test will determine the trouble shooting direction.
If no power then test the break pedal switch. Confirm power into the switch.
If power then more wiring tests needed. IE suspect a break in the wiring harness as the wire path should be good straight from the fuse to the high mounted brake light.
Again it's vital that the trunk grounds be confirm good or a huge wild goose chase could be in your future.
1999-2004 MY fuse panel schedule:
http://www.allfordmustangs.com/foru...r-swap-wont-fire-please-help.html#post2669271
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I have already tested the brake pedal switch and it IS working, as I hooked up a bypass wire and put a test light to it and the light goes on and off when I hit the pedal. I also tested it right at the switch and it works as well. There is also power in fuse 41. The grounds in the trunk may be a possibility. The only one I know of is on the left side new the trunk hinge and it looked OK anyway. Are there any more? I also noticed there is some kind of module near that ground. Any idea what that is for?
wmburns
SN Certified Technician
So IF there's power in fuse F2.41 and no power at the 3rd high mounted brake light the logical conclusion is a break in wiring harness.
The module in the trunk is the fuel pump driver module (FPDM),
Again If this were my car I would confirm the trunk ground before chasing a wiring harness fault.
A set of Ford wiring diagrams is almost a must tracking down a wiring harness fault. If interested in getting a set for yourself I maybe able to help. PM if interested.
The module in the trunk is the fuel pump driver module (FPDM),
Again If this were my car I would confirm the trunk ground before chasing a wiring harness fault.
A set of Ford wiring diagrams is almost a must tracking down a wiring harness fault. If interested in getting a set for yourself I maybe able to help. PM if interested.
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