Hello,

hoping someone can shed some light on this....

i got an 87 Iroc. My center mount brake light does not work.

I have been doing some research on this site and cannot find exactly my problem.

All the lights in car work fine. Main brake lights work.

I have replaced the bulbs. i have also tested for 12v at the connector pad next to hatch motor and i do get voltage there when the brake pedal is depressed i have 12v. This leads me to believe that the switch by the pedal is good........or maybe not?

I grabbed a spare battery that i have and i used jumpers from the battery to the "tabs" that are on the hatch (spring piece) and the light works when i do this. this tells me the wiring in the hatch is ok.

Also with the hatch closed. i measure voltage at the connector in the wing and i get 12 volts there as well.

another thing i tried was to jump the pad next to hatch motor to the "tabs" on the hatch and no go.

im really scratching my head here. I got 12v at the pad with pedal depressed. no voltage when pedal is released.

thoughts.....

 

Check to see if the tabs are maintaining contact when the light bulb is in there. Sounds like an issue I had a long time ago. All I did was bend the tabs a bit toward the inside and its been working like a champ for over ten years now since I did that.

 

I'll try that and see if anything changes....thanks.

However if say this was the issue is it still possible for me to get 12v at the connector in the wing (hatch closed) .

Just throwing that out there.

Admittedly the ground connector is a bit bent (hatch open) to hopefully something that dumb fixes it.

 

Hello,

I had the chance to do more work on the car today and what i eventually found was very odd...at least to me.

When i check for 12v at the lamp connector its good 12V.

when i connect a light....either test light or the light bar voltage drops to 0.34v... obliviously not enough to make the light work.

All other lights work on car.

i took the pad off (next to hatch motor) and used a jumper cable to measure voltage at the wire. when there is nothing after (no light/test light) i get 12v......

when i use a pair of jumper cables to connect a light and read voltage i get 0.34v again.

i know the problem has nothing to do with the hatch. must be from the main wiring.

What could couse this issue. How could i fix it or simply bypass it to make that 3rd light work.

help.... thanks,

 

Highly likely to be your brake light switch .

How ? You ask , when the regular brake lights work ?

Well , your brake light switch is actually two switches in one enclosure . There are 3 wires connected to the switch ;

Orange = +12v input to switch

Light blue = switched contact feeding normal brake lights

Light blue with black tracer = switched contact feeding third brake light

If you check the light blue/black wire at the switch (with pedal pressed and the rest of the circuit in place as in a closed trunk lid) and see anything less than 12V , replace the switch .

 

Thanks for the reply.

The way your described the troubleshooting makes it seem like the switch.

I'll try that tomorrow and report back.

 

Hello,

Went and picked up a new brake light switch and go figure. Everything works now!

Thanks for the tip.

Cheers,

 

Very happy to hear of your success !

 

Hi there,
I realize this is an old thread, but it is related to my problem. I have a 1986 sport coupe with the hatch-mounted 3rd brake light, that is not working. So far I have tested the voltage at the pad (1st picture) and I have 12 volts between the left and right pads, pad 1 and 4 (l to r)


I took the cover off and found that there are 2 wires on the (2nd pic) spring-loaded connector, (left) black wire and (right) blue wire. The black wire was pinched by the mounting bolt, so I cut the pinched section out and soldered the ends together.


I took the light bulb cover off, and all connections look okay, and the bulbs are intact. The silver wiring strips bonded to the hatch glass don't appear to have any breaks in them.


Does anyone have any ideas how to test this further?

 

Put a piece of cardboard behind the spring loaded switch on the hatch and see if that is your problem, might not be making full contact. That was my 3rd brake light problem.
If that's what's happening then you can stretch the spring a little,but I would check that 1st.

 

Hi Mantaguy,
I tried the piece of cardboard, and it didn't make any difference. Is there anything else I could try, or look for to solve this?

 

When you tested the pad you said you had 12V,is that with the brake peddle activated?or just always hot?
I was going to say the brake switch itself at the column.
Here's what I got,but this is for the Firebird,most likely the same.

 

Thanks for the response. I should have said that I got 12 volts across 1 and 4 when the brakes are on, and zero when the brake light is off. So I think the switch is okay.

In the hatch, the blue wire and the black wire both connect to one black wire which connects to the silver stripe that is bonded to the glass. Is there a way to test this section of wiring?

 

I encountered a similar issue, but it's on my 1989 ASC GTA which uses a hybrid of lights similar to the 1989 IROC rear spoiler CHMSL for a 3rd brake light. All GM parts, so should work just fine, and did...

I have the lower brake lights, no problem.

(PIC #1) Measured output at the trunk pad. 12.4 volts.

(PIC #2) Measured at end of harness when trunk closes. 4 volts.

(PIC #3) Measured at the 5 bulb fixture, just after the connector to the end of the harness. 0.0 volts.

Thoughts?


Here's a few pics for reference. Thank you in advance for any insight.

 

Back in 2015 I helped the original poster with this problem , and hopefully I can help you

Looking at the wiring diagram you can see that there are actually two separate switches for the brake lights , one for the lower lights and one for the high mounted light(s) . I have seen a couple of instances where the switch goes defective for the high mounted light(s) but still indicates 12 volts at the trunk pad on a meter with the bulb load removed from the circuit (trunk open) . What happens is that the contacts of the switch get so pitted and burnt that with the load of the bulb(s) connected no current can flow through the bad switch contacts , and the circuit reads zero volts . But remove the bulb load and 12 volts appears to be present , why ? The answer lies in the sensitivity of your meter , which presents almost zero load to the circuit while taking it's measurement . The burnt/pitted switch contacts can still pass the microamps required to give a meter indication , but cant pass the 1/8th amp or so required to light the bulb(s) .

A good way to check this is to use a 12V test light of the incandescent type (not LED) to check for the 12 volts at the contact pad , use a taillight bulb and socket and touch the two wires to the pad and with your assistant pushing the brakes see if it lights up . Chances are that it won't , and that it'll be the brakelight switch (half of the brakelight switch actually) that is the culprit here .

 

So, update from the other day....

I now have 12 v at the end of the harness, but nothing on the "board" or fixture for the 5 brake light bulbs.

ZERO Volts

 

Still putzing around with this, looks like the flapper part of the trunk lid, the two contacts "bridge" differently. That's my interruption in continuity, apparently.

I can place wire from the lower pad, directly to each "pin" and then the 3rd brake light now lights up.

So, where to get this part?

 

Hi
I have the same problem,
Did you ever sort it out?
Thanks
Shawn

 

On a 1986 Camaro, if I delete the trunk motor and the sill electrical contacts, will the third brake light still work? Which years had a manual trunk mechanism (non electric)?

 

No the CHMSL will not work. It is powered by the spring-loaded hinged contact pins making contact with the pad below when the hatch is closed.

1982-1985. However it is a different mounting pattern for the pull-down unit on your 1986-early 91 from the earlier 82-85 style. Also there was an alignment pin on the hatch and a slot below that it enters to ensure the hatch is correctly centered as you slam it shut.

Lon

 

I had this same issue and replacing the brake light switch did the trick! My regular brake lights worked but the high mount didn't. The switch was supplying power to the regular brake lights but was failing to supply power to the high mount brake light.

Very satisfying repair.

 

So i have a trans am, I deleted the trunk motor and the sill electrical contacts, will the third brake light still work? because its not currently working

 

The sill electrical contacts are for the third brake light. Without it the third brake light will not work.

 

so inside of the truck, when i chk for 12 volts on 1 and 4 i have power just on 1 nothing on the 4. on the hatch where there is suppose to be 2 metal connections stick on to go on 1 and 4 i only have one and nothing on 4. i guess it broke off. when the brake is depress and hatch closed, i have a black and red wire on the 3rd stop like they both have power. fyi, when i turn defrost the left side has power and the right side does not. if that makes a difference

 

Good Afternoon! Was checking my car today and found my 3rd brake light didn't work but the other brake lights did. Worked on it for a bit and no elect to those lights at the rear of the car. Thought I'd check on here and sure enough I found this thread, and the switch was what was wrong. Just a long-winded way to say Thanks!