No brake lights.

[77chevy400]

I put a new fuse in just to make sure that the fuse wasnt the problem. Even though the 'old' one was fairly new.

Grabbed a 2 connector brake light switch from a 86 at work. Plugged the connector into both. Still didnt solve my problem.

I used my test light and checked all my fuses under the dash. All of them light up the test light when u press the probe aganist both sides of the tester. However my brake fuse does not. While looking at it i probbed both sides and only the lower side lit up.


Im clueless and got me a nice ticket for this today so im looking to solve this immediatly.

Fyi. I had the brake pedal depressed when i used the test light.

Do you guys think its my mfs?

I have turn signals, parking lights and liscence plate markers. So everything but the brake lights work.

Ive tried changing fuses. Looked at the bulbs, changed them sides.. Looked under the truck its never been in a accident so i dont see it being a broke line. The harness was covered with dirt.

My turn signals when u turn rither one on after uve made a turn it dosent cancel itself. The handle tip has broken before and someone put a knob on it.

I also dont see how a MFS could cause no brake lights.

Any insights?

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[77chevy400]

I never had the chance to check power to the orange and white brake seitch wires. But i think i found y problem.

I was curious and tired of reading so i checked power all my fuses had 12 volts besides the brake light fuse. (Below round fuse, top left).

When i probed both terminals with my multimeter, it showed 0.01 now i never paid attention much in the electrical course but 0.01 should be a open circuit. And open means a bad ground.

My next question is where are the grounds for the brake lights?. I know theres at least two, one for both sides on each brake light housing but shouldnt there be a third for the cab area?.

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[chengny]

Check for 12 volts coming into the brake light switch.

Pull the connector off the switch tabs. Ground the test light properly, and then stick the probe into the slot on the connector that corresponds to the orange wire.

If you get 12 volts into the switch on the orange wire, check that the switch is closing and you get power out.

Leave the connector off the switch. Connect a jumper from the orange wire slot of the connector to either tab on the switch. Test light grounded, put probe on the other switch tab. Press the brake pedal.

While looking at it i probbed both sides and only the lower side lit up.

That's very weird.

When you say you probed both sides, you don't mean that you put the ground lead on one side and the probe point on the other do you?

I assume you mean that with the ground lead clipped to a good clean ground point, you touched the probe point to the top and bottom of the fuse separately.

When you touched the lower fuse clip, which is the line side ("inlet" side) - the light on the probe lit up. Correct?

But when you did the same thing to the top end of the fuse (the load side), the probe did not light up. Correct?


Do your emergency (hazard) lights work? They share the same fuse with the brake lights.

Anyway, check power into and out of the switch and come back.

 

[77chevy400]

Check for 12 volts coming into the brake light switch.

Pull the connector off the switch tabs. Ground the test light properly, and then stick the probe into the slot on the connector that corresponds to the orange wire.

If you get 12 volts into the switch on the orange wire, check that the switch is closing and you get power out.

Leave the connector off the switch. Connect a jumper from the orange wire slot of the connector to either tab on the switch. Test light grounded, put probe on the other switch tab. Press the brake pedal.

While looking at it i probbed both sides and only the lower side lit up.

That's very weird.

When you say you probed both sides, you don't mean that you put the ground lead on one side and the probe point on the other do you?

I assume you mean that with the ground lead clipped to a good clean ground point, you touched the probe point to the top and bottom of the fuse separately.

When you touched the lower fuse clip, which is the line side ("inlet" side) - the light on the probe lit up. Correct?

But when you did the same thing to the top end of the fuse (the load side), the probe did not light up. Correct?


Do your emergency (hazard) lights work? They share the same fuse with the brake lights.

Anyway, check power into and out of the switch and come back.

I will run the testd u said. That i did not do.

Yes i used a properly grounded test light. I probed the bottom portion of the fuse and the tester was bright. Probed the top and it did nothing.

And no my hazards do not work either.

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[77chevy400]

So i probbed both sides of the brake switch wires with it still attaches to the switch it was a real pain to snatxh it out so i didnt.

When i probbed both wires. Nothing happen. Mind u this was w/o me pressing the brake pedal. Bad wires?

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[chengny]

There is something very unusual going on with that fuse holder (15A STOP LPS/TRAFFIC HAZ).

You're absolutely sure that the fuse is good - right? You didn't just look through the glass to check the wire - you checked it for continuity with a meter?

I see where you have tried a different fuse (one that works in a different fuse holder) - so I guess that's proof positive that the fuse is okay.

But you can understand why I am at a loss for any explanation as to why you get 12VDC on the line side of the fuse and nothing on the load side.

If the fuse is good, and the clips on either side are tight enough to make contact with the metal ends of the fuse....if there is power available on the line side there should also be power on the load side.

Try one thing:

Push the fuse into the clip but only on the line side end (the end that tests hot). The fuse will then be sticking out of the fuse block at an angle (or straight up it doesn't matter) - as long as the load side is out of it's clip and the metal tip is up in the air.

With the fuse like that, check again for voltage at the load side (unclipped) end of the fuse.

 

[77chevy400]

Ill check wen im off wrk again with a new fuse instead of switching them. And no i looked at fuse to see if it wont blown n it wasnt how do i use a multimeter to check load and continuity

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