Electrical Brake Light Switch

Shane8996GTLX · Nov 23, 2017

I took the test light and followed the red/gr wire from front to back where it splits off to the third brake light. I'm assuming that means it's a ground issue since I have confirmed power of the wire ?

General karthief · Nov 23, 2017

Now do the opposite, hook the test lead to known power and trace your grounds.

Shane8996GTLX · Nov 23, 2017

Where are all the ground on a 96 mustang bc I haven't found a good diagram

General karthief · Nov 23, 2017

Each light socket has 2 wires, one is power, the other is ground.
I'm figuring you found power all the way to the light sockets correct

Shane8996GTLX · Nov 23, 2017

Yes I did the test light to both sides

wmburns · Nov 23, 2017

Shane8996GTLX said:
Where are all the ground on a 96 mustang bc I haven't found a good diagram

The brake lights are grounded at G300 for the 1996 Model year. Per the Ford service manual:

G300 Below rear of center console

There are also several splices between the trunk and center console area.

But the ground can be confirmed in several different ways. One method is the extend the lead of the test light to where it will reach the battery positive. This will allow the test light to light when the probe is grounded. Confirm that the light works by touching to bear metal in the trunk. Better yet located the green grounding terminal fuel pump ground on the left side of the trunk.

Once it is known that the test light works, then touch to the ground connection of the brake light. IF the ground is good the test light should light. IF not, then the ground isn't working.

For further proof of the diagnosis put the test light on the power side of the rear brake lights. The test light should light each time the brake pedal is pressed.

General karthief · Nov 23, 2017

Do it how wmburns discribed and be spacific with the results, I couldn't describe it better.

Shane8996GTLX · Nov 24, 2017

Ok so I didn't have much time today to figure things out. I saw a black ground wire that runs to the emergency brake below center console. I put new brake bulbs In. I have a feeling fuse 1 15 amps is faulty. And needs taken out for further assessment. Test light won't read/light up but will on one side with fuse removed.

wmburns · Nov 24, 2017

There may be a problem with I/P #1, but it's NOT what is causing the 3rd high mount brake light to not work. The high mounted 3rd brake light goes through I/P #9.

Also note that I/P #1 is only supposed to have power in "run". Did you have the key in run when the test was done?

Besides the very first test was to verify power at the brake on/off switch. Soooooo it's seems very odd to me why dropping back to a possible fuse problem.

Shane8996GTLX · Nov 24, 2017

No power with the key on run For fuse 1.

Shane8996GTLX · Nov 24, 2017

If there is physically bolted ground wires in the trunk I haven't seen them but like you stated under the center console rearwards I only saw e brake ground

General karthief · Nov 24, 2017

Now I'm confused.

Shane8996GTLX · Nov 24, 2017

Sorry ! I'll just keep trying to figure it out

General karthief · Nov 24, 2017

Did you veryify grounds at the brake light sockets?

Shane8996GTLX · Nov 24, 2017

Yes but I can do it again in case I missed something. I know G300 or whatever is a ground but like I've stated a few times, I don't see any other ground besides the one on the parking brake.

General karthief · Nov 24, 2017

I meant at the sockets, I don't think there is a wire back there in the tail light area that grounds to the body, I want you to verify power and ground at the sockets for the third brake light, two wires, one ground, one power,

Shane8996GTLX · Nov 24, 2017

I'll look into this tonight or tomorrow.

wmburns · Nov 24, 2017

Shane8996GTLX said:
No power with the key on run For fuse 1.

Is the key in run power in/out fuse I/P #1, #10, and #7? IF no power in all (3) fuses THEN there's a failed ignition switch.

IF there's power in the other I/P fuses but not in in I/P #1 then there's either there's a fault INSIDE the I/P fuse box or an error in the test.

OBTW, there's TONS of other systems also grounded at G300. Seem like IF the ground itself were bad then other things would be affected. So it seems more likely to me that a spice point or there's a break in the wire itself between G300 and the trunk.

Shane8996GTLX · Nov 24, 2017

Just fuse 1. Funny the test light doesn't pick it up but the volts meter will.

wmburns · Nov 24, 2017

Shane8996GTLX said:
Just fuse 1. Funny the test light doesn't pick it up but the volts meter will.

^^^^This is a dead giveaway that the connection is not capable of carrying current. The test light places an actual load on the circuit. Sooooooo IF the VOM says there's voltage but the test light does not, be on the look out for a high resistance connection.

Corrosion, Water, Rodents!!

Electrical Brake Light Switch

Shane8996GTLX

General karthief

wonder how much it would cost to ship you a pair

Shane8996GTLX

General karthief

wonder how much it would cost to ship you a pair

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wonder how much it would cost to ship you a pair

Shane8996GTLX

wmburns

Shane8996GTLX

Shane8996GTLX

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wonder how much it would cost to ship you a pair

Shane8996GTLX

General karthief

wonder how much it would cost to ship you a pair

Shane8996GTLX

General karthief

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Shane8996GTLX

wmburns

Shane8996GTLX

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