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Old 01-25-2020, 10:53 PM   #1
Jeff M
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Default Brake Light Switch Backwards

I installed a new harness recently and everything worked fine, but the rear brake lights stay on until I depress the pedal. The car is a '30 with two rear tail lights and I'm using a '28-'29 brake light switch.

I figured it might be a ground issue but the brake lights work just not correctly. I don't have the engine pans installed, maybe I need to run a ground strap from the bell housing bolt to frame? I did disassemble the brake switch and made sure everything was aligned prior.
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Old 01-26-2020, 07:36 AM   #2
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Default Re: Brake Light Switch Backwards

What does the ammeter show before you press the brake pedal and then as you press the brake pedal?
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Old 01-26-2020, 09:24 AM   #3
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Default Re: Brake Light Switch Backwards

I cannot think of a scenario where it isn't the switch itself though I am not an electrical expert. Can you test e switch for resistance- zero when pedal is engaged, infinite when not depressed.
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Old 01-26-2020, 10:13 AM   #4
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Default Re: Brake Light Switch Backwards

Did it work correctly before you replaced the wiring?

To be sure of what you're saying,,,, the brake lights stay on after your foot leaves the brake pedal and you then have to lift up on the brake pedal to get the lights to turn off?

Depress = lifting the pedal up?
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Old 01-26-2020, 12:49 PM   #5
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Default Re: Brake Light Switch Backwards

Depress = pressing down. The brake lights are on without touching the pedal, when I press it down they go out. They did work before but I was using a 30-31 switch, I had to use a 28-29 this go around after a modification.
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Old 01-26-2020, 02:09 PM   #6
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Default Re: Brake Light Switch Backwards

If the ammeter shows a discharge when you press the brake pedal, even though the light is out, that would indicate that pulling the tab in the brake light switch is creating a short circuit rather than closing the circuit to the light. That's why I asked about the ammeter.
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Old 01-26-2020, 02:18 PM   #7
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Default Re: Brake Light Switch Backwards

I believe the 28-29 and 30-31 brake light switches work differently. I think the 28-29 is normally off and the 30-31 is normally on. In other words, the 28-29 switch doesn't complete the circuit until the plunger is pulled out by the link from the brake pedal. The 30-31 switch plunger is depressed by the brake rod to open the circuit (when the brake pedal is in it's at rest position) to turn off the brake lights, and when you step on the pedal the spring loaded plunger in the switch pops out and completes the circuit.
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Old 01-26-2020, 02:19 PM   #8
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Default Re: Brake Light Switch Backwards

Is this how your switch is mounted??
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Old 01-26-2020, 06:51 PM   #9
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Default Re: Brake Light Switch Backwards

The switch probably works fine. To check the switch just use a test light or volt meter. Make sure you have constant power to the switch. On the early transmission mounted switch there should be no power thru the switch until the pedal is pressed. On the the later crossmember mounted switch there should be power thru the switch and the pedal when pushed opens the switch.

Where is the early type switch mounted ? It needs to be mounted as the early type switch on the transmission. That switch is normally open. Depressing the pedal then closes the switch and therefore the circuit.

The 30-31 switch mounted on the crossmember is normally closed and releasing the pedal on that type switch opens the circuit.

Last edited by Patrick L.; 01-26-2020 at 08:58 PM.
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Old 01-26-2020, 06:51 PM   #10
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Default Re: Brake Light Switch Backwards

somehow duplicated

Last edited by Patrick L.; 01-26-2020 at 09:00 PM.
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Old 01-26-2020, 09:06 PM   #11
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Default Re: Brake Light Switch Backwards

Quote:
Originally Posted by alexiskai View Post
If the ammeter shows a discharge when you press the brake pedal, even though the light is out, that would indicate that pulling the tab in the brake light switch is creating a short circuit rather than closing the circuit to the light. That's why I asked about the ammeter.

I don't have the engine ready to fire yet, I was just testing the wiring off the battery.

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Originally Posted by Patrick L. View Post
The switch probably works fine. To check the switch just use a test light or volt meter. Make sure you have constant power to the switch. On the early transmission mounted switch there should be no power thru the switch until the pedal is pressed. On the the later crossmember mounted switch there should be power thru the switch and the pedal when pushed opens the switch.

Where is the early type switch mounted ? It needs to be mounted as the early type switch on the transmission. That switch is normally open. Depressing the pedal then closes the switch and therefore the circuit.

The 30-31 switch mounted on the crossmember is normally closed and releasing the pedal on that type switch opens the circuit.

I have it mounted in the correct spot, I'm using an aftermarket battery box with hydraulic brakes.
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Old 01-26-2020, 09:56 PM   #12
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Default Re: Brake Light Switch Backwards

OK, the older type switch. Should work the same way. Do you have power to the switch ? I know you do, or, pretty sure you do. It may be as simple as the power lead is attached to the wrong switch terminal. Power still should not go thru the switch until the pedal is pressed far enough to close the switch. A test light, voltmeter or continuity meter will show which terminal is which.
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Old 01-26-2020, 10:17 PM   #13
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Default Re: Brake Light Switch Backwards

With no pull on the switch rod, the switch should be spring loaded to be OPEN. If it isn't, then remove the cover and see if the contacts are mounted incorrectly. I've seen it happen on the 28-9 switch, and possible because someone messed with it and assembled it wrong.
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Old 01-26-2020, 11:31 PM   #14
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Default Re: Brake Light Switch Backwards

If you have hydraulic brakes why not use a hydraulic switch? Seems to me it would by way more reliable.
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Old 01-27-2020, 06:15 AM   #15
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Default Re: Brake Light Switch Backwards

Good morning Bob,

I will not disturb this electrical feed. But please tell me that part on the universal gear.


Thanks at all!
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Old 01-27-2020, 07:57 AM   #16
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Default Re: Brake Light Switch Backwards

It looks like something aftermarket installed to isolate the transmission from the frame, (cushion it). Maybe it's part of the float a motor I've read about on here?

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Good morning Bob,

I will not disturb this electrical feed. But please tell me that part on the universal gear.


Thanks at all!
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Old 01-27-2020, 07:59 AM   #17
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Default Re: Brake Light Switch Backwards

Yep, that's the float-a-motor transmission bracket. Looks like an aluminum version?
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Old 01-28-2020, 12:26 AM   #18
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Default Re: Brake Light Switch Backwards

Quote:
Originally Posted by Patrick L. View Post
OK, the older type switch. Should work the same way. Do you have power to the switch ? I know you do, or, pretty sure you do. It may be as simple as the power lead is attached to the wrong switch terminal. Power still should not go thru the switch until the pedal is pressed far enough to close the switch. A test light, voltmeter or continuity meter will show which terminal is which.

Yeah I didn't think the wires mattered which terminal they were attached to due to the design of the switch. I'll probably swap them just to see.


Quote:
Originally Posted by Tom Wesenberg View Post
With no pull on the switch rod, the switch should be spring loaded to be OPEN. If it isn't, then remove the cover and see if the contacts are mounted incorrectly. I've seen it happen on the 28-9 switch, and possible because someone messed with it and assembled it wrong.

I'll pull it apart tomorrow and see if anything is incorrect inside.


Quote:
Originally Posted by Ruth View Post
If you have hydraulic brakes why not use a hydraulic switch? Seems to me it would by way more reliable.

Not really, most hydraulic switches fail quite often and when they do you have to open the system to replace it. A mechanical switch will also light up the brake lights faster and is much easier to replace. I figured utilizing the factory style mounting of a '28-'29 switch and pedal pull setup was the easiest route.
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Old 01-28-2020, 01:06 AM   #19
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Default Re: Brake Light Switch Backwards

Re "most hydraulic switches fail quite often" Maybe you would like to explain that one a bit more or were is that information coming from?
Up at the start of this you said you took it apart, was not sure why you would take a new switch apart, but maybe that has something to do with it.
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Old 01-28-2020, 07:41 AM   #20
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Default Re: Brake Light Switch Backwards

With hydraulic brakes I too would have probably used the master cylinder switch. They were used reliably for decades. But, he decided to use a mechanical switch.
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