True brake light mystery...a puzzle for everyone..Please help me

[Winfaulker]

Hello all.

Ok, so i am stumped with this one, and i definitely need some help before i drive into a canyon, or just get rear-ended . Just picked up a sweet 89 White LX for a sic deal. Brake lights no good though.... So I check the fuse box.. NO FUSE!! sweet, i throw one in... it pops immediately as i push the brake pedal. Hazards don't pop it, so it must be the brake light switch right? Throw in a new switch, still no brakes... bulbs are all good and tail lights light up fine. So now i am thinking its a short. problem is i searched the whole hatch area, and looked as much as possible up by the pedals, everything seems fine. The guy I bought it from said the brakes were always fine until he painted the car, and when he painted it he removed the spoiler. Could this be connected or just a coincidence? is it worth is to pull of the spoiler? basically i am stuck here. please gents, any help is really appreciated

 

[HISSIN50]

Welcome to the boards.

Not to nag or doubt, but did you check *really well* around the brake switch itself (I get lazy because it's so cramped)? It's easy for a wire to get pinched and chafed up there. Happens often.

After that, I would disconnect the 3rd brake light wiring if you can (I dont have a hatch to know how accessible the wiring is or if the 3rd light has it's own connector in the hatch, other than at the light).

Otherwise, loosen the spoiler and see if you can shine a flashlight underneath to see what gives.

Good luck.

 

[87foxstang]

Weird about the spoiler deal but i would take it off to see if anything is pinched. If i were you i would thoroughly inspect the wires as well as putting an ohm meter to all the wires connected the the brakes to see what wire is screwed up..

 

[nunly94gt]

i vote pinched on the break switch somewhere, although it could be in the spoiler.

 

[hotcobra03]

wires

hey ,my pc crashed the other day during a rain storm and i lost the big file i was going to send you,,,im waiting on another email to get it back,,,but i did read another post where the guy gave a link with his screen name and password..i want it too..give me acouple of hours ill find it and pass it on..he says hes an electrican and this is all he does,,,wires

 

[bubba-dough]

Since the spoiler was removed and then the problem started, look there first. There is the wires that run through the hatch and into the spoiler for the third brake light. I bet that is the problem. If not, check around the switch and harness. The bulbs not being popped means nothing actually because electricity is looking for its quickest path to ground, therfore too much I or E will never get to it to pop it. Check all your harnesses. Then start checking for shorts on the brake light hot side. This is easy, no fuse needed or power needed. At the bulb, undo the harness and get the brake light hot wire. Stick a multimeter lead in that prong and put the other multimeter prong to a good ground. Switch the multimeter to continuity. If it has a short the multimeter will ding, ring or do whatever yours does to confirm continuity. This continuity means that your hot wire is touching ground somewhere and needs to be repaired.

 

[Mustang5L5]

If the fuse was missing then he had to pull it out meaning he was having probs with the brake lights and took the easy way out.

You say he removed the spoiler?? As in for good? In that case what did he do with the 3rd brake wiring?


I'd do a visual inspection of the wiring around the hatch area (esp the 3rd brake light wiring) and see if anything jumps out at you first. Then i'd start to go to town with a mutlimeter.

I have the wiring diagrams for an 1988 Mustang handy.

According to my diagrams, the brake light HOT wire is a Red wire with a Light Green tracer from the brake switch all the way to the lights themselves. It passes through three connections : C219, C216 and C405 and the 3rd brake light can be disconnected through C453

However depending on if your car is a stick, auto, coupe vert or hatch, the wiring is slightl different. I'd check C453 first (if checking the 3rd brake light wiring doesn't pan out). It's located above the LH rear wheel well in the interior right above where the shock bolts. There are three plugs there. 1of them is an 8-wire black connector and another is a 2-wire black connector. The 2-wire goes to the 3rd brake light. Unplug it, pop your fuse in and hit the pedal and see if it holds. If it does, the prob is in the 3rd brake wiring. if it pop, the prob is in the main taillights.

Then disconnect C405 which is the 8-wire connector. This will kill power to all the brake lights. Pop the fuse in and hit the pedal and see if it blows. If it does, the pinch is somewhere in the body wiring. Connector C216 is by your left foot and can be checked as well if needed

Red with light green tracer is your wire from the switch back.



PS: I highly recommend anyone who has to work on their car's electrical to pick up one of these manuals. They are old and hard to find but if you search Ebay they pop up once in a while. Mine has helped me out DOZENS of times. It's all electrical and vacuum diagrams and shows you how the wires run, what colors they are, where the connections are, etc. It helps to know how to read an electrical diagram though. I'm an engineer and electrician..so this stuff is easy for me

 

[bubba-dough]

Boy that is some bad troubleshooting practice! Please DO NOT pop fuses in to find shorts. This is absolutely the WRONG way. There are very easy ways to find shorts for free (fuses cost money, a hassle, and this way can cause other potential failures).

EDIT: I just seen this in your post. I AM an electronic and electrical engineer, and by your troubleshooting techniques I say

I'm an engineer and electrician..so this stuff is easy for me

 

[Mustang5L5]

Boy that is some bad troubleshooting practice! Please DO NOT pop fuses in to find shorts. This is absolutely the WRONG way. There are very easy ways to find shorts for free (fuses cost money, a hassle, and this way can cause other potential failures).

Ok, Crack out the DMM and substitute popping in fuses for checking the resistance of wires while unplugging the connections and use that method instead. You are right i shouldn't have described such a hack method. It makes me look bad.

He still needs to do a visual inspection beforehand anyway and check he spoiler wiring like i suggested. If he doesn't find anything they he'll have to start opening up the connectors and test the actual wiring.

So instead of popping in fuses, I'll retract and say just use your DMM instead to check resistance values to ground.


PS: I was referring to reading electrical diagrams when i made that comment

the brakes were always fine until he painted the car, and when he painted it he removed the spoiler. Could this be connected or just a coincidence? is it worth is to pull of the spoiler?

PSS: I think his prob is in his spoiler wiring, The PO prob pinched the wiring when he put the LX wing back on the hatch since the wiring lays loose. I bet if he yanks off the wing (easy to do BTW) he'll find the wiring pinched between the spoiler and the hatch. He may be able to tape it up or he'll have to cut and splice the wiring to repair it, but i think the most he will have to do is yank the spoiler off, find the pinched wires, re-splice and heat shrink to repair them and carefully put the spoiler back on and that's the end of it. It's always the most logical thing.

 

[Winfaulker]

Thanks for all the responses guys, I have not had a chance today to mess with it... Darn work... I have a half day tomorrow, and I am committed to finding the problem. I just dug out my DMM which I haven't used in forever and I am gonna find that short. Makes sense, I guess, that it is in the spoiler, I guess the best way to start is to test the connectors by the shock... All this info is great, I really appreciate guys... I'll keep ya posted

 

[Mustang5L5]

I wouldn't even test the connectors. First thing i'd do is pull the spoiler off. It's very simple. I think they are 8mm nuts but not sure.

 

[hotcobra03]

lites

was searching for that link,,no luck yet,,but i seen you posted in another mustangsite...you told a different story in that one..the hassard button was stuck,,and the flasher is bad..whats up wit that..let these guys know more on what was tryed and done..this site is way better that the other one,,a lot more action on here...

 

[Mustang5L5]

Well that does change things since the stop light circuit shares some of the wiring of the hazard circuit.


I'll post up later with more connections to check

 

[hotcobra03]

lites

try lloking at this http://www.chiltonlibrary.com/content/images/8815/images/88156w09.pdf

 

[Winfaulker]

was searching for that link,,no luck yet,,but i seen you posted in another mustangsite...you told a different story in that one..the hassard button was stuck,,and the flasher is bad..whats up wit that..let these guys know more on what was tryed and done..this site is way better that the other one,,a lot more action on here...

Yeah, my blinkers weren't working before, it wasn't a bad flasher, just the hazard switch... I haven't pulled it out yet but i think the connections in the back are either loose or corroded... The blinkers didn't work but when I smacked the hazard switch they turned on, the blinkers that is. If I turn the hazards on i have to repeat this process. The other weird thing was that the hazard flasher spot in the fuse panel was empty and would not accept a flasher, looked like wires were running into the front of it, I don't really know if this is how it is supposed to be. The flasher in the back, is intact. going now to test some circuits and pull of the hatch. I will keep you guys updated

 

[Winfaulker]

Ok... fixed the hazard issue, loose connections on the harness on the back of the switch,,, blinkers and hazards work in harmony, no smacking necessary. This did not affect the brake issue. I am getting about 4 ohms from the red with green wire, from what i understand this wire sends power to the back. All the bulbs test fine though...??? These wires were def. getting hot, the ones on the switch that is... I had to seperate them and tape them up.

 

[nunly94gt]

Are you getting power to the lights? Use a stick on the pedal and check for power when the brake is pressed.

 

[Mustang5L5]

Which wire was getting hot? The Red green stripe wire??


You can try disconnecting it on the driver's footwell. The connection is C216. Remove the plastic kick panel and look for the main "thick: harness. There will be two 8-pin connections there. One will have a black plug, and the other a grey plug. The grey plug will have the stop light wiring in it. You should see the red green stripe wire in the bundle there.

Unplug it, and test the wiring. See if it clears up the short and hot wires at the MFS on the column.

If it does, you know the problem is further down towards the taillights. Might be time to pull the interior panel off and open those connections.

Still curious to why you haven't pulled the spoiler off yet. It's a lot easier than yanking half your interior out to get at the two plugs by the rear shock.

 

[Winfaulker]

Spoiler nut pinching wire for the win lol... I cut out the pinched wire and re -pliced it, She seems to be working now. I appreciate you guys help, this board id awesome..I am hear to stay!!!

 

[bubba-dough]

Otherwise, loosen the spoiler and see if you can shine a flashlight underneath to see what gives.

Weird about the spoiler deal but i would take it off to see if anything is pinched.

i vote pinched on the break switch somewhere, although it could be in the spoiler.

Since the spoiler was removed and then the problem started, look there first.

I think his prob is in his spoiler wiring, The PO prob pinched the wiring

Spoiler nut pinching wire for the win lol... I cut out the pinched wire and re -pliced it, She seems to be working now. I appreciate you guys help, this board id awesome..I am hear to stay!!!

See sometimes we all think alike