Hot Rods Replacing inline brake light switch

Have to replace a faulty brake light switch. Not done one before. Have ordered up the Harley version I have seen mentioned in other posts on the HAMB.

Am I right in understanding that if someone keeps pressure on the pedal I can replace it without having to bleed the brakes?

Looks like the last time this was done thread tape was used. Presuming I do the same?

 

No peddle pressure. Remove and replace, all should be fine.

 

What he said. Beat me to it.

 

Just make sure when you pull the old one you have the new one right beside you and ready to go back in, do it quickly....

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It's a tapered pipe thread, so thread sealer might be useful...or the part might come with some already applied?

or someone will mention that the tapered threads on brake parts are self sealing.

 

Agree with previous answers, assuming the switch location is below the master cylinder. If not then air will enter the system. How much will depend on how fast you complete the changeover. If just a little then you can bleed at at the switch.

 

Everyone above is spot on. I just did this a couple of weeks ago. Switched it quickly, used just a couple of wraps of Teflon tape, switch is about even with the master cylinder. No problems. The Harley-Davidson part number you'll want is 72023-51E. It is physically smaller than most on the market, but it works, which is also different than most on the market.

 

And the Harley switch has different terminals.

 

Just did one one screw out screw in no pressure.

 

Yep, I tossed a HD switch in the glove box along with a pigtail I made to adapt it to my roadster's harness. The one I started with failed with only a few miles on the car. @Kim Strobeck "donated" one out of his Model A stash so we could make an event the next day, that was years ago, and it is still working so why replace it? It is old, rusty, and works perfectly!

No need to hold the pedal, just have the new switch ready to install with some thread sealant on it. Wham, bam, thank you ma'am.

 

I had a NOS Chevrolet in-line, brake light switch from the late-1930's in my '37 Chevy coupe for over 30- years. I had installed it when I converted to DOT5 brake fluid. Both switch & brakes were still working fine when I sold the coupe. Same switch, same brake fluid and I drove it 2k to 3k miles every year.

 

As I don't use this type, I prefer electric switch on pedal, I have a question.

Does this switch need to ground? If so does using Teflon interfere with that ground?

Thanks, just curious.....

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No ground needed.

 

Thanks fellas, hopefully it turns up tomorrow and I get it done.

 

You don't want someone's foot on the pedal unless you like gettng brake fluid in your eyes. you do not want pressure on the system when you change it.
As others said, it is best if when you unscrew the old one you have the new one in the other hand to screw back in.

 

No ground the way you are thinking, the switch simply interrupts a signal, open or closed. We use them to switch the ground lead. Brake light switch/bulbs have power but no ground, press the pedal and pressure in the line closes the switch, ground complete, lights on. Pretty foolproof...as long as the switch doesn't fail. Millions of cars and bikes use this style switch.

 

I had about 3 hydraulic ones go bad on our 57 . Added a relay to take the load off the switch, never had one go again.

 

Thanks fellas.

Have installed the new switch but alas still no brake lights.

Switched the wires on the terminals and still no brake lights.

Connected brake light wiring behind the switch to 12v and they work.

Quick sanity check please. The wire to the switch should be powered when ignition is on?

 

The wire to the switch should be powered all the time if it's an American car, or only when the switch is on if it's foreign. In other words, you can do whatever you feel is best for you.

 

Thanks Jim. Will run a wire direct to the switch and see how I go

 

Anyone reading this and want to test a switch, scroll to the 6min section of this video.

 

I hate those things, just from a high failure perspective. Maybe an NOS would last. I used to do fleet maintenance for an airline. I replaced a bunch of them like the guys so far have described, so I don't have any of them in my cars. The other style never fail.

 

I have similar thoughts, and gave up on them a while back, but according to a few comments on here the Harley Davidson ones last.
Others state that they need to be installed vertically or on top of the fitting, which mine wasn’t.
Although I don’t understand how the brake switch without air in the system would know the difference.

 

I’m with squirrel. I’ve had much more success sealing pipe threads with sealant/dope than with Teflon tape. As others have said have the switch treads coated and ready to go and do it quickly, no pressure on pedal. Do not over tighten.

 

Power in power out when pressure is present on the switch (closing the contacts) or manually closing them without it hooked to the master. If you have power into one side (doesn't matter which side) and no power out with brakes applied, you have a bad switch. Jump both wires together off the switch and test the rest of the circuit. The old mechanical brake light switch from a Chevy truck works great (all my cars have been converted to these), but even these you need to find a good quality switch.

 

so was the original switch faulty or was it just hooked up wrong ?
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Maybe-needy-brake-bleedy

 

I keep all of the old pressure switches from parts cars although the original in my Fargo is still working flawlessly

 

@panhead_pete ,
Test with wire as Jim suggested. If that fixes issue, you're finished.

If not, test switch as shown in video. If switch is good, it may have air bubble.
Have your helper pump brake pedal and hold down. Loosen switch slightly, air and fluid will be released around threads. Tighten switch. Release brake pedal. (Same process as bleeding a wheel cylinders brake line).

 

The hydraulic switches require a certain amount of pressure to activate, it's more than a little .. In this day of distracted/ incompetent drivers , it's good to use all the means of protection available . A mechanical switch can be adjusted so it only needs a small bit of movement with virtually no pressure , the big difference is I can activate the brake lights whether I'm actually braking or not . Especially when you drive a manual transmission car & use engine braking , doing so provides no warning to the distracted soul behind you , if you're coming up on an area. Where you know you're going to reduce speed , you can touch the pedal as a means of letting the guy riding your tail know that you are slowing down without actually braking . Some things to consider before you choose a type of switch .