electrical problems

newmnfn

New Member
Jun 12, 2018
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#1
hey guys so I have a 03 GT 4.6 L automatic my turn signals and all 3 brake lights went out today so after looking at all the forums this is what I've done replaced fuses, relay, turn signal switch, brake switch, now the car is stuck in park I'm lost any help would be great cause I really want to fix it myself and not tow her to a shop. I do have running lights and back up and the tails are leds of that helps thanks
 
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wmburns

SN Certified Technician
Aug 14, 2009
4,743
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Houston Texas
#2
Stop. Take a breath. Now stop "changing parts" trying to fix an electrical problem. <joke>

Now if you do not have a Volt-Ohm meter (VOM) or a test light your next step is to get one. They are not expensive and could easily be purchased from the money saved by not replacing parts that are likely good. Even better is to have both in your tool box. If the $$'s are real tight and you have to choose only one, then choose a test light if you mainly work on cars.

Today's cars have tons of "always on" circuits. Which means they are powered even if the ignition key is off. Did you disconnect the battery negative when doing the work? If not, then likely fuses have been blown.

Note, no where in this reply are you going to be asked to replace anything without confirming it first. Why? Because to correctly trouble shoot this issue we need to know the status of the parts as this gives us important information. You will be asked to confirm power in and out of specific fuses. Not just "check" the fuse. The best way to do this is with a test light. Put the lead of the test light on a known good ground. Always confirm that the test light works before performing any tests. There is a small piece of metal that is accessible out the top of the fuse. This gives an easy way to "probe" the fuse to check for power. A good fuse will light the test light on BOTH sides. In that way power has been confirmed in and out of the fuse.

The shift interlock depends upon fuses F2.17 and F2.35. Test for power in/out of fuse F2.17. Next test for power in fuse F2.35 with the brake pedal pressed. The ignition key doesn't need to be on for these tests as these are always on circuits.

If no power into fuse F2.35, then there's a fault in the brake light circuit and more trouble shooting is needed.

If you are into testing fuses, not a bad idea to also post the status of fuses F2.33, F2.41, F2.18, and F2.13. It's not clear to me exactly what works and doesn't work after replacing parts. Nor is it clear to me if the fuses replaced were blown and if they blew again after being replaced. Again it's vital to know the correct ID of any blown fuse.

F1=BJB=Battery Junction Box=engine bay.
F2=CJB=Central Junction Box=driver's kick panel

1999-2004 MY fuse panel schedule:
http://www.allfordmustangs.com/foru...r-swap-wont-fire-please-help.html#post2669271
 
Last edited:

newmnfn

New Member
Jun 12, 2018
9
0
1
38
banning ca
#3
Stop. Take a breath. Now stop "changing parts" trying to fix an electrical problem. <jo

Now if you do not have a Volt-Ohm meter (VOM) or a test light your next step is to get one. They are not expensive and could easily be purchased from the money saved by not replacing parts that are likely good. Even better is to have both in your tool box. If the $$'s are real tight and you have to choose only one, then choose a test light if you mainly work on cars.

Today's cars have tons of "always on" circuits. Which means they are powered even if the ignition key is off. Did you disconnect the battery negative when doing the work? If not, then likely fuses have been blown.

Note, no where in this reply are you going to be asked to replace anything without confirming it first. Why? Because to correctly trouble shoot this issue we need to know the status of the parts as this gives us important information. You will be asked to confirm power in and out of specific fuses. Not just "check" the fuse. The best way to do this is with a test light. Put the lead of the test light on a known good ground. Always confirm that the test light works before performing any tests. There is a small piece of metal that is accessible out the top of the fuse. This gives an easy way to "probe" the fuse to check for power. A good fuse will light the test light on BOTH sides. In that way power has been confirmed in and out of the fuse.

The shift interlock depends upon fuses F2.17 and F2.35. Test for power in/out of fuse F2.17. Next test for power in fuse F2.35 with the brake pedal pressed. The ignition key doesn't need to be on for these tests as these are always on circuits.

If no power into fuse F2.35, then there's a fault in the brake light circuit and more trouble shooting is needed.

If you are into testing fuses, not a bad idea to also post the status of fuses F2.33, F2.41, F2.18, and F2.13. It's not clear to me exactly what works and doesn't work after replacing parts. Nor is it clear to me if the fuses replaced were blown and if they blew again after being replaced. Again it's vital to know the correct ID of any blown fuse.

F1=BJB=Battery Junction Box=engine bay.
F2=CJB=Central Junction Box=driver's kick panel

1999-2004 MY fuse panel schedule:
http://www.allfordmustangs.com/foru...r-swap-wont-fire-please-help.html#post2669271
hey there ok so I've done that what about going back to the stock light
 

newmnfn

New Member
Jun 12, 2018
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banning ca
#4
ok so in using an ohm. meter all fuses check out so and I'm getting power to those that were suggested and still having problems where should I go next
 

newmnfn

New Member
Jun 12, 2018
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#5
ok gents so I got the car to drive fixed my shift lock problem but the original problem still haunts the car I'm thing a new ground cable on the rat side fender or something is wrong in the rear harness cause I have power at the fuse block while the brake pedal is being pressed so again no stops or turns but I do have running lights and back up lights just any more help with this please guys I'm begging
 

wmburns

SN Certified Technician
Aug 14, 2009
4,743
319
154
Houston Texas
#6
Does the high mount 3rd brake light work?

If the high mounted 3rd brake lights does work but the turn signals do not, it is either:
  • burned out bulbs. Note in the case of LED lights you are aware they will not work if the plus/minus is backwards.
  • loose or not connected ground.
  • wiring fault
  • multi-function switch.
If the high mounted 3rd brake light does not work then CONFIRM the ground in the trunk. Best to confirm all the way back to battery negative.

What did you do the fix the shift interlock problem?
 
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newmnfn

New Member
Jun 12, 2018
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#7
the 3rd brake light is out as well as both right and left lights I have no turns or stop and no 3rd brake I've already replaced multifunction switch and all bulbs are brand new I'm tracking grounds cause idk what else it can be as far as the shift lock with the battery connected I used a ohm meter checked f2 35 and f217 f2 17 was found to be popped so I unhooked the battery negative cable replaced fuse also went thru and checked every fuse in the terminal no others were found bad reinstalled negative cable and vehicle was able to shift I'm still so dumb founded that I'm not getting any results on why no stop or turns please please help
 

newmnfn

New Member
Jun 12, 2018
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0
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banning ca
#8
what's puzzling is I have running lights fog lamps and the dash lights and interior dome work perfectly where would the ground on the trunk be found and does the harness have a split in the trunk where i could check to see if the other side of the connector is getting power and my trunk harness is bad I'm really just guessing here cause I'm so puzzled by this whole thing but my local auto supply house is loving me also they are puzzled as well since we feel like we have done everything.
 

wmburns

SN Certified Technician
Aug 14, 2009
4,743
319
154
Houston Texas
#9
Ok, just be be clear. You have CONFIRMED there is power in and out of fuse F2.35 when the brake pressed. This is important as an incorrect test result here is going to lead you on a "wild goose chase" of epic proportions.

As a reminder there a MULTIPLE ground locations through out a car.

Have you CONFIRMED that the 3rd brake lights is capable of working by powering directly from the battery or some other power source?

You have the ability to answer all of your questions. If this were my car I would attach a long piece of scrap wire to the test light and connect to the battery negative. Touch the test light to battery positive the confirm the test light works.

Go to the third brake light and remove a bulb or split the harness. With a helper push the brake pedal and then lightly probe the body harness terminals. The test light should light when the power side is probed. As I often work by myself I take a 2x4 and jam between the brake pedal and the seat.

To test the ground move the test light pig tail to battery positive. Confirm the test light works by touching battery negative. In the same manner, the test light will light when the other body electrical connector is probed IF the ground is good.

What to do next depends upon the EXACT test results.

If asking me to handicap this thread..... There is more to the story than what's in this thread. With a blown fuse F2.17 there is a real possibility that other damage has been done as fuse F2.17 powers the shift interlock and the cruse control. So either the fuse blew by going through the shift interlock (not good) or there's a wiring fault some where in the harness. Of course this could all be explained away if during the work something was accidentally shorted out and this has been since corrected.
 

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