March 23, 2019, 04:24:02 PM

Author Topic: Brake Light Switch Wiring issues  (Read 140 times)

Offline GarrettW

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Brake Light Switch Wiring issues
« on: March 13, 2019, 04:56:19 PM »
Would anyone be able to help me with wiring up this light to work with my brake switch? Im fuckin clueless on wiring and kinda at a loss, the way it was explained to me I need to merge the ground with the accessory switch  and I clearly did something wrong, because I just melted my power wire out right before the relay.

Im trying to convert a light bar to work as my brake lights. The car I have the chassis harness was useless and I no longer have anything for the original bulbs. My trouble is where you start wiring the brake pedal switch, there is 3 wires on the light bar harness one is blue (goes to the relay merged with the red power wire) one is white ( goes to the relay by itself) and one is the ground.

On the switch there is a green and black wire on the top, and a red and yellow wire on the bottom. I attached the green and black to the ground. The red and yellow to the white. And the blue to my accessory switch.  I then merged the ground wire from the brake switch to the bottom of the accesory switch. Then merged the ground again so I could ground it to the chassis. When I tried to turn it on. The blue/power wire melted to bits.

Online Cobranut

Re: Brake Light Switch Wiring issues
« Reply #1 on: March 13, 2019, 05:55:37 PM »
I'm fairly certain that the brake light switch interrupts the ground on these cars.
+12v power is routed to the bulbs, then through the brake switch to ground. 
When you merged those wires you created a dead short from battery +12v to ground, which will quickly burn wiring.
1995 FD, 7.0 Liter stroked LS3, T56, 8.8, Samberg kit.

Offline GarrettW

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Re: Brake Light Switch Wiring issues
« Reply #2 on: March 13, 2019, 06:28:51 PM »
That makes a lot more sense. If thats the case, how would I stop this from happening? I have an extra wire with a fuse in the middle that I could use  if that makes any difference

Offline Exidous

Re: Brake Light Switch Wiring issues
« Reply #3 on: March 14, 2019, 01:11:59 AM »
Have you looked at the factory manual? Drawing things out can help a LOT. It's pretty hard to visualize wiring when you are taking to a "novice". Hell, two experts can be talking and have no clue what the other is saying.

Also, I <3 pictures and drawings.

Should note, the brakes on most cars have nothing to do with the accessory switch. The brake lights will come on without the key.

It's pretty much:
Battery +
Fuse
Brake Light +
Brake Light -
Brake switch
Chassis

Foot off the pedal interrupts the circuit.
94 BB SBE LS1 Full Mamo top, MS3ProU with TC, RONIN 8.8 and another custom dual 2.5" stainless exhaust. Too loud, need bigger muffler....

Offline GarrettW

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Re: Brake Light Switch Wiring issues
« Reply #4 on: March 14, 2019, 07:55:04 AM »
Yeah Ive read over your messages atleast 10 times and cant find a clue what your talking about. So 12v power, is that the red wire or the green wire? I wish I could understand what your saying, im used to just wiring up red as power and black as ground, but with all this color change on the rx7 pedal and the light bar harness has me thinking like a 3 year old.

Yes I tried reading the service manual, it only confused me more from how many wires they have and it being tied into the ecu.. when you try to “bypass it” i kinda get lost on how it works without it. Here I can just take some pictures for you. Im really not ashamed of how clueless I am. Just wish wiring language makes sense to me lol.

The first photo is where I started crimping the 3 wires for the brake switch/accessory
The second is where they connect to the relay. (Toasted the blue wire good lol) The red/blue went to the top of my acc switch. The red/yellow crimped to white wire go to the bottom of brake switch. The green/ground goes to top the brake switch  while also splitting to the bottom od the acc switch then splitting again to the ground on the chassis.

And Im confused. On the rx7club post about the brake light, ( https://www.rx7club.com/2nd-generation-specific-1986-1992-17/wiring-brake-lights-w-o-stock-harness-963684/ ) they were saying you need it attched to the acc switch so it stays on without hitting the brake pedal for night time and stoof.


If its too hard to explain it to someone as clueless as me. I can take more pictures that maybe wll help. I also attatched a drawing of what I did.
« Last Edit: March 14, 2019, 08:47:47 AM by GarrettW »

Offline Exidous

Re: Brake Light Switch Wiring issues
« Reply #5 on: March 14, 2019, 12:28:00 PM »
So I'll start with don't power anything on at all until we get this sorted. :-)

Your drawing does not include a load(the light/somewhere to send the power to). A brake light doesn't normally need ACC power but the FC does apparently. The night time running lights are tied to the light switch.

Battery + that is always on is red. Battery plus that is switched on by the ACC is usually orange or black w/ white stripe(mazda specific I think). There are other colors as well which is why the manual is so important. Do NOT look at the system as a whole. Your brain will melt. Look at individual circuits and follow the lines one at a time.

Mazda has these simple circuits that control the lights and blinkers. They call them CPU but it's nothing to do with the engine control unit.

On a side note. The FC manuals are complete garbage compared to the FD manuals.

What I've attached is the FC brake light diagram with what I think are the two circuits for the brakes. Rear running lights and brake lights.
94 BB SBE LS1 Full Mamo top, MS3ProU with TC, RONIN 8.8 and another custom dual 2.5" stainless exhaust. Too loud, need bigger muffler....

Offline GarrettW

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Re: Brake Light Switch Wiring issues
« Reply #6 on: March 14, 2019, 01:11:39 PM »
So ive looked at your attachment, and I see that the POSITIVE is actually tied to both brake switches it looks like? Does that mean my white wire AND the blue wire should have been tied to the switches WHILE having a fuse inbetween them? I only have one fuse and its at the battery after the relay. And then the ground was supposed to just go to the top of the acc switch??

Im still pretty confused but I think im getting a little bit farther. I hadnt put the power to the light on the diagram because I already have that tied to the battery and its all good to go. I just cant wire the switch itself. Heres a picture of the harness and then a picture of the brake switch

Offline Exidous

Re: Brake Light Switch Wiring issues
« Reply #7 on: March 14, 2019, 01:15:52 PM »
What two switches are you talking about? You have the ignition at teh top and the brake pedal just before the relay.

Does your light have three wires?
94 BB SBE LS1 Full Mamo top, MS3ProU with TC, RONIN 8.8 and another custom dual 2.5" stainless exhaust. Too loud, need bigger muffler....

Offline GarrettW

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Re: Brake Light Switch Wiring issues
« Reply #8 on: March 14, 2019, 02:34:08 PM »
Sorry I meant to say both brake switch terminals. And the old switch on the harness that I cut out has 3. Thats what i have been crimping with. The light itself only has a red and black.

Offline Exidous

Re: Brake Light Switch Wiring issues
« Reply #9 on: March 14, 2019, 02:42:36 PM »
Without using a resistor and extra relay or computer controlled PWM(pulse width modulation) you will not be able to have running lights and brake lights from one bar. It will be on or off. That's it.

I asked about three wires because you can have a common ground. One red wire is bright and the other is dim.

From the looks of that light you must be planning on permanently blinding anything behind you.
94 BB SBE LS1 Full Mamo top, MS3ProU with TC, RONIN 8.8 and another custom dual 2.5" stainless exhaust. Too loud, need bigger muffler....

Offline GarrettW

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Re: Brake Light Switch Wiring issues
« Reply #10 on: March 14, 2019, 04:22:44 PM »
Ive got thick red film that ill be laying on it to dim them a lot and make them red.

Pretty much didnt see the choice with not having the ability to use the chassis harness

I have the relay from the trashed harness if that can help me? Ive pretty much got to get some sort of brake light to pass tech.
« Last Edit: March 14, 2019, 04:29:29 PM by GarrettW »


Offline DDv8

Re: Brake Light Switch Wiring issues
« Reply #12 on: March 15, 2019, 01:15:50 AM »
https://www.norotors.com/index.php?topic=770.0     s4 wiring diagram  pg 50-58

start at the B on top lines = battery +12v-->G/W (green with white stripe)-->F-18 this is the stoplight plug-->W/G (white with green stripe)-->F-19 cpu plug (the cpu is a 3x10" box mounted next to the fuse pox by the dead pedal.  plugs into the bottom) If you do not have the cpu jump W/G and G (green)-->FR-02 front rear connector (ignore)--> at rear light plugs/harness switched 12v + is the green wire G  the ground wire is B black unless its a convertible then its R red.

the brake light power is as simple as it gets in a fc

86fc old school 327, T5, converting to 8.8 tbird