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Brake lights not working -- issue with combo switch


Locke

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I've spent the past day cleaning the turn signal switch contacts on my 1970 240z to fix some electrical issues. The left/right blinkers now work, but I'm still having trouble getting my brake lights to work. After installing the cleaned TS switch, the brake lights worked initially but then stopped working-- so I tore it apart again to make sure that the contacts connecting the signal from the brake switch to the tail lights were clean. Upon reinstalling the switch they still do not work.

I've confirmed that I get 12v on the green/yellow wire from the 6-pin connector that goes into the TS switch harness. I've also confirmed that when the TS switch is plugged in to the connector that I have continuity from the back of the green/yellow wire on the dash end of the 6-pin connector to the soldered end of the green/yellow wire on the combo switch. However, as soon as the combo switch is plugged in to the 6-pin connector I no longer get a 12v reading anywhere along the green/yellow wire.

I then took the combo switch apart again and plugged everything in. I found that when the metal contacts in the switch from the brake signal to the tail lights were engaged that I always got 0 volts no matter if the brake is depressed or not-- and more interestingly, the brake signal has continuity to ground when these contacts are engaged. However, when I move the metal contacts off of the taillight connections, I get a proper 12v when the brake is depressed on the metal piece that the green/yellow wire is connected to.

It appears that somehow the rear lights being connected to the brake signal somehow connects the brake signal to ground, meaning that the 12v coming from the brake switch never reaches the tail lights. I don't understand why this is happening when the rear lights function perfectly when using the left or right blinkers (so clearly the 12v from the TS flasher is successfully driven to the tail lights). Though the blinkers work, my hazard switch does not appear to work (I know that turn signals/brake lights are run through the hazard switch). Can anyone help me solve the issue with my combo switch before I give up and buy a new one? Thanks!

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Did the brake lights ever work? 

Here is a breakdown of the circuit: https://fiddlingwithzcars.wordpress.com/2013/01/20/hazard-switch-brake-light-turn-signal-circuit-analysis/

Voltage measurements are a reference. Where are you putting your leads when you measure?

There should not be any voltage on the green/yellow wire at the turn signal switch until the 6 pin connector is plugged in and the brake pedal is depressed. If you are seeing 12VDC to ground at the green/yellow wire when the pedal is not depressed or when the 6 pin connector is unplugged, that is a problem.

With the 6 pin connector unplugged, check voltage to ground at the green/yellow wire on the dash harness side with the brake pedal depressed. 

Also bench test the turn signal switch with resistance readings.

If the brake lights worked at one time but don't work now, my first guess is that the rocker for the brake lights is not making contact properly.

image.png

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6 hours ago, SteveJ said:

Did the brake lights ever work? 

Here is a breakdown of the circuit: https://fiddlingwithzcars.wordpress.com/2013/01/20/hazard-switch-brake-light-turn-signal-circuit-analysis/

Voltage measurements are a reference. Where are you putting your leads when you measure?

There should not be any voltage on the green/yellow wire at the turn signal switch until the 6 pin connector is plugged in and the brake pedal is depressed. If you are seeing 12VDC to ground at the green/yellow wire when the pedal is not depressed or when the 6 pin connector is unplugged, that is a problem.

With the 6 pin connector unplugged, check voltage to ground at the green/yellow wire on the dash harness side with the brake pedal depressed. 

Also bench test the turn signal switch with resistance readings.

If the brake lights worked at one time but don't work now, my first guess is that the rocker for the brake lights is not making contact properly.

image.png

Thanks for the reply and your help!

I've just gotten the car back from the shop after a full restoration, so the brakes haven't worked since I've had it. I've also spent the past several days on that FiddlingWIthZcars post (love the diagram on there).

When measuring the voltage, I'm putting one lead on the pin connected to the green/yellow wire in the 6-pin connector and the other on a bolt connected to the body (ground).

Here's where it gets confusing: I do get a 12VDC reading on green/yellow when depressing the pedal if the 6-pin connector is not plugged into the TS switch (measuring through the front of the connector). When I plug the 6-pin into the TS switch and measure at the same spot (by back-probing the connector), I no longer get the 12VDC upon pressing the pedal.

Additionally, I've cleaned the rocker for the brake lights and ensured there's no resistance-- and that they make proper contact with the leads for the rear lights in the combo switch (as your picture shows).

I currently have the TS switch plugged into the car, but with the combo switch disassembled so that I can see the electrical contacts (as in your picture) and physically maneuver them. The blinkers still work in this configuration when I physically tilt the teeter-totter to contact the leads for a particular side. When I ensure that the brake rockers are contacting the rear light leads, I still get 0VDC across the rocker whether the pedal is depressed or not.

However, when I use my fingers to pull back both sides of the brake rocker so that they don't contact the leads for the rear lights, I get a proper 12VDC across the rocker when the brake is depressed and 0VDC when it is not.

TLDR: I am getting 12VDC on the green/yellow wire if the TS switch is unplugged and the brake is depressed, but get 0VDC on the wire once the switch is plugged in. If I don't allow the brake rocker in the combo switch to contact either plate connecting to the rear lights, I also get 12VDC when the brake is depressed. As soon as the brake rocker makes contact with the leads again the voltage drops to 0.

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Your response doesn't change what I said before. Do the tests I suggested and report the results.

If the switch was reassembled properly, you should not see voltage at the green/yellow wire when the 6 pin connector is unplugged. The only way you would see voltage there with that connector unplugged is if it's cross-connected with the turn signals.

 

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My apologies, I must be misunderstanding your first response. What other tests would you like me to report back on?

Also, when I say that I get 12VDC on the green/yellow wire when the TS switch is unplugged and I press in the brake, I am measuring on the dash harness side. There is 0VDC on the switch side of the green/yellow when it is not plugged in (so it is not cross connected to anything).

Thanks again for the help

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That makes more sense. 

You may want to get a terminal kit like this: https://www.amazon.com/gp/product/B07VKCCN12. It comes with a crimping tool. You could make a jumper with an inline fuse (See https://www.amazon.com/BOJACK-Holder-Inline-Values-Assortment/dp/B0813Q4S6P) and install it between the green/yellow and white/red (or white/black) wires on the dash harness side of the 6 pin connector. You could press the brake pedal to see if the brake lights on one side lights up. If the brake lights come on, then you can focus more on the turn signal switch.

Also at the 6 pin connector on the turn signal switch measure resistance between the green/yellow wire and to the white/red wire. Repeat between the green/yellow and white/black. You should see close to zero ohms. If you have high resistance (or open line) that would indicate an issue with the turn signal switch.

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Quick update—

I’ve measured and confirmed that there is 0 ohms of resistance between the white/black and green/yellow as well as white/red and green/yellow on the TS switch.

With the TS switch unplugged, I again confirmed that I get 12v on the dash side of the green/yellow wire when the brake is depressed.

I followed your suggestion and connected the pins from the green/yellow to the white/red using a piece of wire on the dash end of the 6-pin. When they are connected and I press in the brake pedal, neither tail light lights up and there is 0v across the wire connecting the two pins.

I removed the white/red end of the wire and measured again and found that I still get 12v upon pressing the brake when it is only connected to the green/yellow (just to confirm that the wire is seated properly and works).

I repeated this test with the pin for the white/black wire and got the same results.

This leads me to believe that the issue is downstream of the TS switch in the brake light circuit.

The only thing that confuses me about this is that the rear lights work perfectly when using the blinkers. Does this have something to do with the fact that the brakes use an additional bulb compared to the blinkers/running lights?

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Actually, your test results give me a different conclusion. The problem is upstream of the turn signal switch. Here is why I say this:

  1. The turn signals work.
  2. The hazard lights don't work.
  3. You have the proper resistance measurements at the switch.

The jumper at the 6 pin connector was to eliminate the turn signal switch as being the problem. With the behavior being the same as with the switch connected, it reduces the chances that the switch is the problem.

If the problem was downstream, the blinkers would have the same problem since they share the wiring from the switch to the taillights.

The hazard lights and brake lights are powered off the same circuit.

There is a good chance that there is corrosion or a damaged wire/connection in the circuit. Either condition is like a clog forming in the pipe between the water main and your house. If you measured water pressure with no faucets open, the pressure looks fine. However, run your washing machine, the shower, and the hall bathtub at the same time, and you will find you don't have any water pressure inside your house.

So how do you find and remove the "clog" in your wiring? The easiest thing is to check your fuse box first. Look for corrosion or bent/poor contacts at the fuse. Look for corrosion or deteriorating contacts on the backside of the fuse box. Make sure the connectors between the dash harness and fuse box are in good condition and free of corrosion. 

Don't be afraid to take photos of your fuse box and post them here. I can only make "logical" guesses without seeing things or working with a meter on your car.

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Thanks so much, with your help I think I've narrowed down the issue to the fuse box.

I measured and found that the resistance across the contacts of the fuse labeled "Flasher" is incredibly high (around 85 ohms). I'm guessing that flasher means the hazards (correct me if I'm wrong).

unnamed.jpg

In the above pic of the back of the fuse box, you can see a huge black glob on the other side of the contact for that fuse. It also looks like the green wire under that glob that supposedly connects to the contact isn't connected to anything.

I've just ordered the MSA upgraded fuse box, so once it is delivered I'll install it and report back.

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55 minutes ago, Locke said:

Thanks so much, with your help I think I've narrowed down the issue to the fuse box.

I measured and found that the resistance across the contacts of the fuse labeled "Flasher" is incredibly high (around 85 ohms). I'm guessing that flasher means the hazards (correct me if I'm wrong).

First, thank you for posting the photo. It does take some guesswork out of trying to figure out what's wrong with your car.

Now in response to your post, okay, you're wrong. 😉 Flasher is for the turn signals. The brakes and hazards are on the same fuse.

image.png

There has been a lot of carnage in that electrical system. The black/white wire feeding the turn signals has melted off most of the insulation. I'm surprised you were getting turn signals.

The fuse for the running lights/gauge lights has experienced the very common meltdown. It looks like the wire going to the contact was cut off, so I would be curious where the IPO (idiot previous owner) was getting the power for that circuit. I also see damage on the wire for the horn circuit, but that was probably from when the running light fuse melted down.

Definitely perform a careful inspection/cleaning of the light sockets for the side markers, front marker/turn signals, and the rear marker/turn signals/brakes. I should have taken a photo of one of the side markers I took off my 240Z a few months back. It was rusted beyond reasonable repair, so I replaced it with a cheap replica I purchased from ebay. If there isn't much corrosion, Spray the socket with Caig Deoxit and use a small wire cup brush on a Dremel to clean off the corrosion. In a pinch, you can also soak the socket in Tarn-X instead of Deoxit, but I would rinse with denatured alcohol to get rid of as much Tarn-X as possible. Also, don't run power through anything treated with denatured alcohol until you are very sure it has all evaporated.

Using LED bulbs for the side markers, turn signals, and brake lights will also drop the thermal stress on the wiring and switches. I also like LED headlights to take the load off the switch. You can get decent H4 housings (I like Hella) and H4 headlight bulbs for about $140 from Amazon. Let me know if you want more details.

I noticed that you put a pin on the member map that you're in Georgia. @gogriz91 and I know many people in the Atlanta area for parts/work on Z cars if you're ever up this way.

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I would suggest for you to pull your dash harness, unwrap and inspect every terminal and wire and repair or replace as needed.

Those white/ red power wires get very hot and under the outer dash harness plastic/ tape covering, they can melt insulation on smaller wires and cause them to contact each other whilst uninsulated.

It is not hard, it  just takes not a small chunk of time to unwind or meticulously cut the outer dash harness.

I use zip ties to keep it all together after and avoid an outer covering to easily identify any issues which may further transpire.

 

Edited by dhp123166
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