Brake Warning Light Testing

[mattyv87]

Based on all of this is there a good step by step method to troubleshoot a non working brake warning light. I understand that there could be a few different reasons the warning light would not light up but I am looking for some guidance on troubleshooting.

I started with the easiest thing and replace the brake warning light bulb. I have a newer brake warning connector at the H block. I plan to install a new ignition switch next week.

When I directly ground the warning light housing the bulb lights up.

Thoughts?


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If the two wires going into the brake warning switch connector are both grounded with the ignition turned to on, it should have the brake warning light illuminated as I understand it. Therefore, with the switch connected but removed from the H block depressed as well as grounded, it should also illuminate. A long jumper to test grounds at multiple points could help pinpoint a ground issue. This is basically my next step as well.

Check to see if you have good ground to the chassis, firewall, dash and engine. This is probably majority of this circuits problem.

 

[Oldtimer]

When I directly ground the warning light housing the bulb lights

The stock brake warning lamp housing has a floating ground.
The bulb does not ground thru the housing.
It has 2 wires, R/Y, and Violet (purple).
R/Y wire, supplies 12v from ignition switch in RUN position.
V wire, is ground thru pressure differential switch or thru ignition switch in START position only.

If you ground the warning lamp housing, with the key on, and the bulb illuminates
Look for:

1. A short between the housing and V wire.
2. A short between lamp housing and outer shell of bulb socket (maybe the spring when installed in dash).

 

[msommer001]

Good morning,
I was able to do a bit more on this today. With the in the “ON” position, I grounded the brake warning housing, bulb did not illuminate. Then I grounded the point that the violet with white strip wire connect to the bulb socket, the bulb illuminated.

I previously checked the back side of the ignition switch for ground to and when I checked it with my circuit tester, it illuminated, indicating that I had a good ground. Is there another way to check ground at the ignition switch?

At this point, I am going to replace the ignition switch to see if that corrects my issue.

Thanks again for the continued input.


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[DirtDonk]

Easy to check the ground with a test lamp, or an ohm-meter.
Find the little side tab that was pointed out previously in the thread, remove the wire connector from it, and use your ohm-meter probes between that connector and a known good ground. Or the test lamp from battery power to the tab.
If the meter goes to zero, or the lamp lights up, when you turn the key to START, your ground is sufficient for lighting the brake warning lamp.

 

[Slowleak]

Test your new switch before you install it. You don’t want to find out that it is bad after you install it like I did. Those things are no fun to remove.

 

[jerry]

Test your new switch before you install it. You don’t want to find out that it is bad after you install it like I did. Those things are no fun to remove.

This... Is sage advice!

 

[msommer001]

Ignition switch arrived today. Install tonight. I will report back.


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[msommer001]

I was able to get into the garage. Replaced the ignition switch and tested before I reinstalled. Brake warning light lit when I bumped the key into the start position. I put it all back together and for some reason the warning light would not light up.

I did a bunch of testing and it seems like the ignition switch failed/broke. Is it common for a new ignition switch to work one moment and not the next. Going to get another switch tomorrow and try it all over again.


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[DirtDonk]

Is it common for a new ignition switch to work one moment and not the next.

Far, far too often.
In fact, if you buy it from the same source, or get a replacement, or warranty part from the same source, it’s not uncommon for multiples to fail in one way or another.
Might be dead right out of the box, might get a couple of good starts on it, might work for six months.
But if it can fail, a modern part is built to do just that!

Welcome to the modern world of electro, mechanical replacement auto parts. Sourced from multiple overseas locations and built to spec.
Unfortunately the only “spec” followed anymore seems to fall into one category. Lowest possible price.

 

[Oldtimer]

Verify you have ground between switch housing (installed) and battery.
Can be rust or paint between (deep breath) switch, dash, cowl, inner fender, ground wire under starter relay mount, block, battery post.

 

[msommer001]

Verify you have ground between switch housing (installed) and battery.
Can be rust or paint between (deep breath) switch, dash, cowl, inner fender, ground wire under starter relay mount, block, battery post.

When the switch is installed I have good ground on the back housing of the ignition switch.


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[msommer001]

I got a new switch, tested it before I fully installed and then installed if fully each time the brake warning light lit up when key was in the start position. For now this is done…now on to the next project.

Thanks again for all the input and guidance along the way.


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