Brake Light Switch

[Merle Coggins]

Well, it's no secret here that I've had short life issues with brake light switches. I've been using switches from Napa and they've been good about replacing them under warranty, but I've had enough. So I ordered up a couple from Rock Auto to try a different manufacturer. This morning I switched out the failed one with a new one and all is good again. I also rechecked how much juice the brake lights were drawing. I connected my VOM in Amp meter mode and measured 4.5 amps. I started up the truck and brought up the RPM so that it was charging at 7.3 volts. That brought up the amperate to 5.05 amps. This should not be too much for the switch.

I carefully cut the top crimp off of the failed one and had a look inside. The contacts were all black and carboned up. I took a piece of emory cloth and with just couple of swiped one cleaned up easy. (see the pics) What's causing this? There's nothing unusual about my brake light circuit. Battery power, from the headlight switch breaker, feeds the brake light switch and the output from the switch runs to the back and tees off to the two lamps. I even have a ground wire from each tail lamp assembly going to the frame to ensure a good ground.

We'll see how long this one lasts.

Dirty contacts

One contact cleaned up with a couple swipes of 320 emory cloth

Amp draw on brake lights with engine running and generator putting out 7.3 volts

After fixing this I tinkered with a couple other items, gave it a bath, and went for a ride. It was good to get it out on the road again. However, I found that my turn signals aren't working now. That gives me something else to tinker with.

Merle

[John-T-53]

Merle -

Maybe try an NOS switch...maybe VPW has them? I'm not sure if my switch is original to the truck, but I've never had a problem with it in the ten years I've had it. You would think a simple part like this would be hard to get wrong.

Maybe there's something in the air up in WI that's leading to your problem...

As a general statement, I've not had really good luck with repro or replacement electrical parts, not for the truck but in working on other vehicles.

When all else fails, NOS.

[tom'sB2B]

I bought a low pressure brake switch from Ron Francis' wiring (www.ronfrancis.com). It seems to have fixed what ever problem I had. I went through two switches before I put this one in.

[norrism1]

Merle, I have found out that brass connectors will last longer then the plated copper. After market appear to be the cheaper copper contacts.

My .02

[Merle Coggins]

Maybe there's something in the air up in WI that's leading to your problem...

Maybe you should come on up sniff of our dairy-air, then let me know what you think.

[Merle Coggins]

Thanks for the feedback guys. That Ron Francis switch must be awesome since it is 4 times the price. But it's good to have options. Thanks for the link.

Merle

[John-T-53]

Maybe you should come on up sniff of our dairy-air, then let me know what you think.

I'll take your word for it! I've had my paint peel just from driving by this place:

http://en.wikipedia.org/wiki/Harris_Ranch

[TodFitch]

I'll take your word for it! I've had my paint peel just from driving by this place:

http://en.wikipedia.org/wiki/Harris_Ranch

I don't think the facility on I-5 is a dairy setup but rather a much more smelly CAFO http://en.wikipedia.org/wiki/Concentrated_Animal_Feeding_Operations

And there is another feedlot that has gone in fairly recently down in the southern part of the Central Valley on I-5 a little north of the US99/I-5 split.

Its been a while since I've visited a dairy but I don't recall them being nearly as smelly as those places on I-5.

[HanksB3B]

Dairy Air... as in clean, earthy, wholesome, natural.

Not like Harris Feed Lot which absolutely does smell like a*s!

Hank

"Drive by Harris's Feedlot. You'll never Eat a Fast Food Burger again"

Edited June 14, 2011 by HanksB3B

[Don Coatney]

On topic. Merle, Have you considered a mechanical brake light switch? I installed one on my car sereral years back and it works great. It trips when I tap my pedal so I can use it to back off tailgaiters without the brakes coming on to slow me down. Pictures below.

Off topic. Glad to see some of you really know your $hit:D

[1950 Special Deluxe]

Don, thanks for the pictures. I did this to my car last night. Very happy with the operation of this setup.

Neil

On topic. Merle, Have you considered a mechanical brake light switch? I installed one on my car sereral years back and it works great. It trips when I tap my pedal so I can use it to back off tailgaiters without the brakes coming on to slow me down. Pictures below.

[NiftyFifty]

On topic. Merle, Have you considered a mechanical brake light switch? I installed one on my car sereral years back and it works great. It trips when I tap my pedal so I can use it to back off tailgaiters without the brakes coming on to slow me down. Pictures below.

Off topic. Glad to see some of you really know your $hit:D

Is this just a jobber piece? I'm just tired of the stupid switches leaking...I'm looking at a 3rd switch in less then 1 year, and not to mention the danger of leaking brake fluid. Do you have any part #'s?

[41/53dodges]

Well, it's no secret here that I've had short life issues with brake light switches. I've been using switches from Napa and they've been good about replacing them under warranty, but I've had enough. So I ordered up a couple from Rock Auto to try a different manufacturer. This morning I switched out the failed one with a new one and all is good again. I also rechecked how much juice the brake lights were drawing. I connected my VOM in Amp meter mode and measured 4.5 amps. I started up the truck and brought up the RPM so that it was charging at 7.3 volts. That brought up the amperate to 5.05 amps. This should not be too much for the switch.

I carefully cut the top crimp off of the failed one and had a look inside. The contacts were all black and carboned up. I took a piece of emory cloth and with just couple of swiped one cleaned up easy. (see the pics) What's causing this? There's nothing unusual about my brake light circuit. Battery power, from the headlight switch breaker, feeds the brake light switch and the output from the switch runs to the back and tees off to the two lamps. I even have a ground wire from each tail lamp assembly going to the frame to ensure a good ground.

Merle

this carbon buildup is likely caused by high current arcing, perhaps even brake fluid leaking in and the arc boiling it.

on another note,

Thanks again for the engine! it runs great, i dropped it in last week, and next time i go up i should be able to take a quick drive if everything works! so thanks again!

[Dan Babb]

Speedway has that switch.

http://www.speedwaymotors.com/Universal-Mechanical-Brake-Light-Switch,1972.html

Trying to visualize how I'd mount it with my setup.

The only thing stopping me from taking my truck for a short spin around the block the brake switch t-fitting leaking really bad.

[mechresto]

Merle

Did a bunch of detective work and I find that what once was a very uncommon failure has now, due to cheapening of construction, become a very common problem. the failure of brakelight switches. It seems that in the past the inner workings of the brakeswitch were far more robust, the contacts were larger and employed a wiping action when engaged. That wiping reduced the arcing and kept the contact area clean. The common "workaround" is to install a relay. The brakeswitch is still used but only to fire the relay using far less current. Heres a link to a place that has what u need (hopefully)

Bryan

http://www.watsons-streetworks.com/relays.html

[Merle Coggins]

Thanks Bryan. I was considering adding a relay but finding 6 volt relays isn't easy and the amp draw I'm getting should be well within the tolerance of these switches. But it's still in consideration.

Josh, good to hear that the Ol' 41 is up and running with that engine. Have fun terrorizing the neighborhood up there with it.

Merle

[mechresto]

Sorry Merle

Did'nt know you were working with 6V ! But anyhoo here's the relay that you need with 6V, the other that I posted is for 12v sorry.

http://www.aecsensors.com/DG85.pdf

On the bottom of the page is the configurator, everything on the page is what the options are for the relay. You spec it, they put it together. Pricing is very reasonable usually $3-$5.

They've saved my butt on several occasions. Some older farm equipment has relays that are getting hard to find, Along with older volkswagon, triumph etc.

Bryan

Edited July 14, 2011 by mechresto

[Merle Coggins]

Cool, thanks.

Merle

[DollyDodge]

My brake light switch went out last month, it was less than a year old.

[coW52Dodge]

Striking how many people have problems with switches so it has me wondering..

There's a fair bit of wire between the switch and the bulbs and am wondering whether it is long enough to introduce some inductance. Inductors, like those in relays, when you take the power off of them, want to sustain the current going through them and actually induce a significant voltage spike of reverse polarity in doing that. It can exceed the normal voltage easily by a factor of 10.

This effect is called 'self inductance' and there is some of that effect in just wire as well.

If just a regular piece of wire is long enough and the current going through it is high enough, it could be that you're seeing a similar spike on the switch contacts when it opens. That could eventually cause the contact to fail because it isn't rated at those voltages.

I'm not saying this will solve it or that it even is the problem, but it is maybe worth a shot, if you're going though switches a lot:

A common way to get rid of that spike is to put an electronic component called a diode across the contact. You can buy these things at radio shack and are often called "general purpose diode" with part numbers like 1N4001. They look like this:

Measure the voltage across the switch while not braking and note which is more positive than the other.

Hook the side with the silver bar (left on the picture) to the more positive side and the other side (right on the picture) to the more negative side of the switch.

If your contacts now last, wire inductance may have been your problem.

[Dave72dt]

You'll have to explain the testing process for inductive better for me to understand it. As far as I know, only one side will be hot when not braking, the other goes to ground through the light. Pressing the brake alows current to flow between the contacts. Finding the hot lead's voltage is not a problem but what am I comparing it to? Where do I put the test leads?

[Merle Coggins]

I am familiar with self inductance in coils and I deal with quenching diodes on solenoids quite often. However, I have a hard time believing that a single wire could create enough inductive current to cause any problems.

Merle

[coW52Dodge]

I am familiar with self inductance in coils and I deal with quenching diodes on solenoids quite often. However, I have a hard time believing that a single wire could create enough inductive current to cause any problems.

Merle

Even straight wire without being wound around air or a core has some inductance.

It has a fair bit of current flowing so likely does create a bit of a field so taking the current away would create some back EMF.

I agree that it may be like grabbing at straws a little but it was just a thought since so many people seem to be having issues with their switches. Maybe the old switches are rated at higher voltages so the problem wasn't prevalent. Voltages generated by back EMF can be significant.

It would be interesting to measure it by hanging a scope on the switch to see what's going on. One may see some high frequency ringing of decent levels.

As far as polarity, measure across the switch but with the brake not applied. With a positive ground and one side of the bulb being grounded, that's the side the bar would be attached to. Not sure if you can identify that wire on the switch so when you're measuring, whatever is more positive, that's what the 'silver bar' side hooks to.

My switch has blade contacts, so you may be able to stick it in the wire contact side, before you attach it to the blade.

Diodes like this are small, sub dollar so could be worth a try. It certainly won't harm anything.