Brake Light Fuse Blows

SableSal

SableSal

Member
Sep 17, 2009
295
3
19
Fresno, Californ-I-A
#1
Well this blows... literally. I need your guys' help on this one! My 95 has a intermittent concern where the brake light 15A fuse will blow at least once or twice a day. It all started after I was driving back from Santa Cruz to Fresno, Ca. About a 2 - 2 1/2 hour drive. I noticed half way back that my turn signals weren't working. I eventually got home and realized not only did my turn signals stop working, but so did my brake lights!! I was like ****!!! So anyways... first thing was first. I was running sequential turn signals at the time, I figured my sequential's were at fault (Web Electric Products). I removed them and decided to solder all the connections rather than the scotch-locks that were supplied with the kit. Take note that I had the sequential turn kit for about a year and a half before this concern occurred. So anyhow I soldered up the connections and installed the kit. Everything seemed to work fine for about a few days, then again... the fuse blows. After messing with it for so long, I decided to sell the kit. Something must be wrong with the kit, and I don't have time to figure it out. I started rolling around bone stock and everything seemed to be okay for about two to three weeks... then the fuse blows. I would replace the fuse and sometimes it would last for days, other times it would last for hours. I tried to pin point when the fuse blows, whether it's when I use the turn signal or when I brake. I can't seem to get it to blow when I want it to blow. I decided to replace the brake light switch in the event that it's bad or grounding or causing too high resistance in the circuit. I replace the brake light switch with a new one and yup... the fuse blows. After some speculation I decided to replace the multi-function switch (turn signal stalk). I ordered one online through rock auto for cheap ($28 shipped). I figure the wiper part is bad, might as well replace it to make it look cleaner and function like it's suppose to function. At the same time, I decided to replace all the bulbs just in case one of them is internally shorted. One other thought I had was the third brake light in the aftermarket Cobra style wing. I'm thinking the LED is a cheaper LED and the issue I have is LED is causing a high resistance in the connection (butt connectors). So I decided to redo the connection at the wing wiring and make it more of a hard wire connection rather than a spliced connection at the wiring with those darn Scotch-locks. After a few drives... the fuse blows. I then thought, the Cobra style wing's LED is the cause of this!! I should disconnect it and continue driving and see if the brake/turn fuse blows, if it doesn't then I know it has to be the LED! Well.. I drove for about two to three days now and guess what... on the way home from work today... the fuse blows. I really can't figure out what is happening. I've searched the forum and I found if you replace the clutch quadrant that the brake wiring near the clutch/brake pedals may wear if not routed correctly. Yeah, checked that. Nope, it's routed right and it's good, no wear. I also at one time modified my trunk so that it deleted the stock third brake light and when I replaced the trunk I replaced the trunk wiring.. Nope seems okay at this time. I'm literally stuck! I don't know what more I should check. Has anyone ever dealt with something like this before? Any tips on where I should look next?

Thanks in advance guys, I'm sure we can figure this out together.
 

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#2
I was going to suggest the exact harness you checked behind the pedals. I had this exact situation in my '94 GT back in 2002. It would blow the fuse whenever the brake and clutch pedals were pushed to full travel simultaneously.
 
#4
I had the same problem with the fuse ramdomly blowing. After going through fuses, brake swithces, bulbs and headlight switch I decided to chase wires. I found that my Steeda aluminum clutch quardrant wore a very tiny hole in a wire above it and would ground it out. It would not blow the fuse while shifting or quick stops. After reparairng the wire and moving the bundle I have not had a problem since (5yrs now). Hope this could be your solution too.
 
#8
I checked it again and I believe I found my problem. Check this out... Brake light wires AT THE CONNECTOR corroded.

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You can see how the corrosion is at the top of the copper exposed area of the wire where it meets the terminal. Also you can see the insulation is very discolored and heat damaged. Looks like I found my issue!

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I still have the wing off, dig it? lol

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Found out that Ford Motorcraft offers a pigtail for the repair. I purchased it for about $25 from my local Ford dealership. Here's what it looks like and part numbers!

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I'll be soldering the connection and heat shrinkin' it all back together soon and report if it's fixed!
 
#10
revhead347 said:
Good info. Thanks for posting all the pics.

Kurt
Click to expand...

Thanks! I kept seeing plenty of started threads, but nothing ever found or finished. I like to stay on task and report my findings, might help someone someday.

Here's how a wiring repair SHOULD look like ;)

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All is done, gonna drive her for a week with everything connected back on and I'll report what happens (crosses fingers!)
 
#11
Excellent follow-up, great info, and nice pictures! We almost need a repair sticky for threads like this one that go the whole nine yards.

Thanks again and I hope your fuse problem is resolved.
 
#12
WhiteCobra95 said:
Excellent follow-up, great info, and nice pictures! We almost need a repair sticky for threads like this one that go the whole nine yards.

Thanks again and I hope your fuse problem is resolved.
Click to expand...

Thanks! I hope so too, I'm going to polish out some water spots under the wing today then put that back on and drive it for a week and see what happens. Hope it's still alive by next weekend! :) I will let you guys know for sure! (crosses fingers)
 
#14
That lug corrosion was from high current through it. The crimp is the highest resistance part of the connector, so it gets hot during overload, heats the wire and causes formation of a copper oxide that flakes off. This oxide looks different than typical copper oxidation and is typical of what your photo shows. Heating in this lug demonstrates that your short circuit is in the circuitry following the switch. In this problem, you are not searching for a high resistance connection, you are looking for a short circuit to ground. A high resistance in any splice will reduce the current, not cause a fuse to blow. The short will be through a component such as a lamp, LED assembly or special purpose module. The short can be from wire to the car's body, or it can be to a ground wire routed to a module, socket or connector.

The node after the brake pedal switch branches out to several places. It goes to the brake lights and high stop light as you already know. It also goes to the anti-lock brake control module if your vehicle is equipped with one. It also goes to the multi-function switch. On a manual shift car, this node routes to the (cruise control) deactivator switch and then goes to the speed control amplifier. It also connects is the power control module. On an automatic, it connects to the shift lock actuator.

These wires will be color coded red/light green. After the deactivator switch, the wire in this node will be a light green wire to the speed control amplifier. The brake on/off switch C242, deactivator switch C260 and brake pressure switch C261 connectors all break out together from a common thinner bundle under the dash next to the pedals. Examine all three of these leads to be sure they aren't touching the clutch cable, clutch quadrant or nearby metal.

You could isolate the speed control amplifier by unplugging the deactivator switch (or the jumper in an automatic application) and running without speed control for a while.

You could have a pinched wire anywhere in the car, especially where wires have been disturbed during servicing. I think you said you changed the multi-function switch, so I'm sure you would have noticed a chafed wire there in the column. Elsewhere in the vehicle these wires are well protected with plastic loom and tape covering, so it's rare to find a short there, especially on a car that's been on the road a while. (pinches tend to be found during warranty phase). It's not unheard of if seats or carpet have been removed though. The more likely places to have a short are where the circuits terminate, such as in lamp sockets or the abs module. I recommend giving a thorough visual examination at the lamp sockets, high tail lamp, and ABS first. The tail lamps are well protected from water entry, but they could still fail. What about the high mounted LED lamp? Is it possible that water got into this assembly? Visual Inspection will show. I don't recall if you disconnected it or were thinking of disconnecting it.

You can measure circuit current by unplugging the related 15A fuse and connecting your multimeter and the 15amp fuse in series at the fuse location. Harbor Freight has these meters for only a few bucks. An analog meter is better suited if you have a choice. Then have someone apply the brakes while you watch current flow on the meter and while wiggling lamp sockets, ABS sockets and so forth. The tail lamps should draw 2.1 amps each. IDK what your LED lamp should draw, probably not more than an amp. You should have around 8-10A in this circuit. A 15 amp fuse will run for hours at 15 amps and not more than 1.5 seconds at 22 amps.

If you think a lamp socket has a short, you can find out which one. Remove the bulbs from the sockets. Hold a toy magnetic compass next to the wire. If there is current flow with the bulb removed, the compass will spin to align with the wire. That proves current flow and there should be non with the bulbs removed.
 
#15
I have disconnected the wiring at the LED stop lamp, and it still blew. I'm thinking I'm after a short to ground. I just haven't the slightest clue where. I've taken the trunk apart as well and nothing looks bad. I've wiggled a couple or harnesses around and nothing. All looks well. I just really need to know where the wiring goes from the trunk, so I can better follow it. I think the short has to be in the interior. Also could be in the front area. I did swap out the front end to a cobra and replaced the header panel when I did the swap. I'm also thinking it could be near the rear seat or center console area, I have been in those areas too. Thanks for your help, I PM'd you hope you get to me so I can get this figured out once and for all!
 
#16
I sent you a PM. I had an idea this morning that may help you search for a short/overload. In place of the fuse, insert a 12 volt bulb. An old prewired tail lamp socket would make this easiest. One should cost a buck or so at the pick-a-part and they are handy to have in the toolbox. Just poke the bare wires into the fuse sockets for the brake light fuse. Be absolutely certain this bulb has no exposed connection that can momentarily touch the car's body. You could tape the wires to the fuse box to make it more secure. If you get one with long leads, you can put in within view from anywhere you're working.

The lamp will light if there's significant current flow into the circuit, but it will limit current to 2 amps even into a short, making it safe to search around. It will light full brightness until the short is removed. That will save $$$ on fuses while you track this down. With all the bulbs removed from the high stoplight and rear stop lights, the test lamp shouldn't light. As you wiggle bulb sockets, connectors and the wiring harness, if the bulb should momentarily light, you've found the location of the short. You might need to disconnect the ABS module if you have one, so it's out of the circuit. If you have an interlock solenoid that prevents shifting out of park until your foot is on the brake (automatic trans application) you may need to disconnect that as well. Actually, an interlock solenoid could be a source of your problem too if you have one. A shorted solenoid or solenoid with a portion of turns shorted would draw too much current. I know the Crown Victoria has one that stops you from shifting out of park if your foot isn't on the brake. Great idea for forgetful old farts like me. I'm not sure about your car. I don't know if you have a manual or automatic. Mustang is new to me; I got a beater 96 last month that I'm restoring.

The harness going to the rear lighting routes from the right lamps, through the rear deck between the tail lights, to the left lamp. Then it goes up over the left wheel panel. To find these, you would have to remove the trunk lining. There will be a difficult clip on the side panels adjacent to the wheels and back seat. Once it's near the back seat, I don't recall where it runs, but I think it will run under the carpet along the driver's side of the car up to the dash. You may be able to snap the left kick panels and then the left sill molding to lift the carpet and look. This might have shifted under the driver's seat mounting or rear seat mounting.

When I'm at the pick-a-part this Friday, I'll look at wiring harness routing. I have the carpet ripped out of a 99 Mustang up there but I didn't pay much attention to the harness. I know there's a wire going to the seat belt, electric seat motors and hand brake lever running under the carpet. Those wires may be there even if you don't have electric seats, IDK. The harness might get pinched under one of the seat mounting locations if it ran nearby. It could also get pinched under the console. I'll check on the routing if we don't have this solved by then.

I forgot to say, you will need someone pressing the brake pedal while you search since these circuits aren't active until the brake switch is closed.
 
#17
Well I had the brake pedal depressed for about an hour yesterday and working the turn signals, nothing blew. Not until I drove a few blocks away, as soon as I did, it blew. Seems like the vibrations of the drive is what causes it to blow. Sounds like the short is near the grounded area and won't hit until the car is in motion due to the vibrations... I tore apart the entire rear seat paneling area including the entire trunk. When the fuse blew this morning, I had the deck lid wiring harness disconnected, so I know my issue is not there. Anyhow I'm at work today and will start looking into the center console today after work. You think any wiring in the center console might be causing my issue?

Also I will be looking into the engine compartment today after work, maybe something to do with the ABS system. I know I'll find it, just getting to that point is frustrating! I will win this! Haha
 
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