Rear/Brake Lights

[Pat427]

I've been able to get all the lights in my MK4 Roadster to work properly except for the brake lights.

The brake lights do not turn on when I press the brake pedal. However, all four lights in the rear of the car will turn on if I activate the headlight switch.

I've attached picture of my brake switch below. I've tried changing the location of where the wires attach, but still nothing.

https://thefactoryfiveforum.com/attachment.php?attachmentid=126790&d=1587345456Anyone have any ideas?

Thanks,
Patrick

[Jeff Kleiner]

You should get all 4 lamps on the low element when the headlights are on. Does the white plunger move when the pedal is depressed? If not you need to adjust the switch. Use your VOM to read resistance between the two switch terminals; it should show open (infinite resistance) when the pedal is released and continuity (zero resistance) when the pedal is depressed.

Let us know what you find.

Jeff

[NiceGuyEddie]

Unless something has changed recently, the 'Fankenstein' sockets can fit in backwards. They shouldn't, but they can. Flip them around 180º to at least eliminate the variable. Of course, they MAY not fit in the other way around, if they don't go in, don't force them.

I had all sorts of problems with ONE bulb in the wrong way. Drove me nuts until I figured it out.

[Pat427]

Jeff, yes the plunger moves outward when the pedal is pressed. In fact, I actually removed the switch from the pedal assembly and kept the wires connected and pressed the plunger in and out, with no luck getting the light to turn on.
I sent you a PM about my voltmeter. Any help is appreciated.

[Big Blocker]

Take the two wires you have shown in your picture and short them together . . . do the brake lights come on?? If not, you have other issues with your wiring. Trace everything from source to end of line. Circuit is 12v power to brake light switch--> out of brake light switch to rear bulbs high element--> bulb grounded. Its a simple circuit.

The headlight switch and the connected tail lights and front marker lights have absolutely nothing to do with the brake light circuit and have only a common ground between them.

That being said, and not knowing HOW you have your rear lights wired (upper, lower, or all four), or if there is a "trailer adapter" involved, it a guess on our part.

Do what Jeff said, test the switch continuity, your removing of the switch and cycling it makes me lean toward your wiring.

Doc

[Jeff Kleiner]

Start simple---is your brake light fuse good?

Jeff

[FFinisher]

Start simple---is your brake light fuse good?

Jeff


bingo! Then test the purple wire for 12v. Then adjust the switch.

[Pat427]

Jeff,

I'm not entirely sure, but the fuse looks a little messed up at the 11 o'clock position?
https://thefactoryfiveforum.com/attachment.php?attachmentid=126815&d=1587433839


Start simple---is your brake light fuse good?

Jeff

[ram_g]

Looks busted to me, but you really have to check the continuity. Having a good digital multimeter is essential to getting the wiring done.

[Jeff Kleiner]

Pat,
Got your message. Learning to use your multimeter will help tremendously with being able to troubleshoot problems like this. Here are a couple of quick tutorials to get you started but there are tons of others:

https://youtu.be/c9KNAIjoEYs

https://youtu.be/RtNMhCzq72M

To check that fuse you'll set your meter to read ohms and put a probe on each side of the fuse. A reading of "I" indicates infinite resistance; i.e. an open circuit---a blown fuse. A reading of 0.0 or very near zero (0.1, 0.2) indicates low resistance; i.e. a complete circuit---a good fuse.

Good luck,
Jeff

[CraigS]

The fuse is blown. Now the question is why.

[RJD]

I know page 12 of the manual shows to connect the brake wires to the rear spades of the brake pedal switch, but try connecting the brake wires to the forward spades. if you do a search, you'll see that others (including myself) had a brake light issue, and this solved it. Here's mine:

126854

[Papa]

I popped the fuse during my build because of what RJD described with the wiring to the switch being incorrect. My blunt-cut brake wires were constantly hot and one of them touched the chassis and popped the fuse. I would have been scratching my head for who knows how long if I hadn't seen and heard the arc when it happened.

[Pat427]

Jeff,

Thanks for the explanation.

So after using my multimeter, it appears the fuse labeled, "Brake/4Way" is blown.

I'll be getting a new one. Question: for Factory Five cars, is there a specific brand or type of fuse I need to get? I'm assuming this is a 15 Amp fuse?

Thanks,
Pat


Pat,
Got your message. Learning to use your multimeter will help tremendously with being able to troubleshoot problems like this. Here are a couple of quick tutorials to get you started but there are tons of others:

https://youtu.be/c9KNAIjoEYs

https://youtu.be/RtNMhCzq72M

To check that fuse you'll set your meter to read ohms and put a probe on each side of the fuse. A reading of "I" indicates infinite resistance; i.e. an open circuit---a blown fuse. A reading of 0.0 or very near zero (0.1, 0.2) indicates low resistance; i.e. a complete circuit---a good fuse.

Good luck,
Jeff

[Papa]

Pat,

Yes, it's a 15 amp fuse. I keep a pile of them in my tool box since they are dirt cheap. I bought one of these:

https://www.amazon.com/gp/product/B07B6LPRZZ/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

It's also a good idea to keep a few in the car along with your emergency tools.

Dave

[Jeff Kleiner]

... Question: for Factory Five cars, is there a specific brand or type of fuse I need to get? I'm assuming this is a 15 Amp fuse?



No, available at every auto parts store in America.

Jeff

[Pat427]

Hey fellas,

I replaced the fuse and BAM! The brake lights are working as intended. Big thanks to all of you for helping me through this issue. I couldn't be more thankful for you guys.