The Stovebolt Site Forums The Shop Area The Electrical Bay Brake Lights Stopped Working

Now what?

This morning as I was preparing to leave for work, I discovered that Ol' Roy's brake lights aren't working. I check lights on vehicles all the time and I know they were working a couple weeks ago , just before I got into the valve cover gasket / rocker arm job.

It's a 6v system. Taillights are working. Bulbs aren't cloudy and the brake light filaments are intact.

The problem seems likely to be at a point that both lights share - wiring, brake light switch. Where exactly is the switch? I don't remember seeing it during other repairs.

I'm at work so I can't look at anything now or flip through the manual unril I get home this afternoon. What's the most likely cause and why would they just stop working when the system hasn't been disturbed lately?

If it has a pressure switch in the brake line, thats where you start looking. I had a few that didn't work reliably so I switched to micro switch. The fluid pressure switches leak and damage the internal contacts. In my case, I could stop the truck with little pressure on the brakes so the lights never activated. Yours maybe mounted on or near the master cylinder.

Otto - The brake light switch is located on the underside of the cab floor kick panel, pretty much directly under the steering column. Screenshots below are the switch info from the Shop Manual and a screengrab of a Denny Graham posted picture of his 1950 Chevy pickup engine compartment showing the actual switch and location.

Since the switch and wire connections are exposed to the elements, the switch and/or the wire connections do fail overtime. Repop switches are available from our usual vendors.

EDIT NOTE: It is a mechanical arm movement electric switch that is triggered by depressing the brake pedal. The brake pedal rod actual move the switch arm between the off/on positions. I've added a pic of the switch by itself from Jim Carters EL106 ad page.

I’ve experienced something like that and issues was the pedal travel. Pull on the brake pedal to see if the light comes on.

Assuming no turn signals have been installed, the brake light switch is the most likely culprit.

To troubleshoot, move the arm of the switch with your finger to see if the lights come on. If they do, the switch is positioned wrong.

If the lights do not come on, short the 2 wires on the switch together. If the lights come on now, the switch is bad.

If you still don't have lights check for battery voltage on one of the wires. If no battery voltage check the stop light fuse on the firewall. If you have battery voltage the problem is wiring from the switch to the tailights or both bulbs burned out.

If you still don't have lights check the problem is either the headlight switch or wiring between the headlight switch and the stop light fuse on the firewall.

Thanks a lot. Talk about a Rube Goldberg contraption. That's funny that the switch has its own lever arm.

I guess I know what I'm doing when I get home from work this afternoon.

I also wasn't even aware that there was a fuse in that stoplight circuit.

Wiring diagram for 50 Chevy truck attached.

On my '46, the brake light switch is located on the firewall on the engine side of the brake pedal. My brake lights stopped working one time and the switch tested OK. My brake light wiring goes through my Signal-Stat 800 turn signal and I ended up taking it apart to spray all the contacts with electronic cleaner. After cleaning, my brake lights started working again and they are still working today.

Fortunately I do not have any add-on turn signals. It has the stock brake light and parking light system. The only modification is a right hand brake light spliced into the original system.

This of course was done decades ago so I don't know anything about it but my guess is that the problem is up there with the switch or that fuse. I forgot this truck even had a fuses. I guess it is like three of them or something.

Actually, it's more likely that the brake lights won't turn OFF if the pedal isn't all the way up. But the switch itself can freeze up so the lever doesn't move or the contacts get corroded. It'll be a two person operation to replace, as it's secured by two screws from inside the cab. One to hold it in place while the other turns the screws after the floor mat has been pulled back.

The filaments in each bulb look perfectly fine. It doesn't seem that just the brake half could be burned out on both of them while the taillight halves still work. Can bulbs burn out with no damage to filaments or clouded, black glass inside the bulb? Doesn't seem likely.

It's possible that both of the brake filaments are burnt out. Check them with a multimeter set to ohms with one probe on the bulb casing and the other on the contact points on the ends. You should get a small number of ohms on both contacts, but they'll be different. If you get an open circuit reading, then the filament is bad.
Check the fuse with a multimeter as well. Those can fool the eye also. But since you get voltage at one of the switch wires, that confirms the fuse is good. Plug that wire into the switch and check for voltage on the other switch terminal as you depress the brake pedal.

Can the filaments be burned out even though there's no visual evidence that they are? All of the little wire filaments and everything in there are still all connected not all messed up like bulbs usually get when they blow.

Bulbs can fool your eye like fuses can. Check with a multimeter.

If all that checks out ok, look for a break in the wiring going to the brake lights. Maybe a rock hit damaged it, causing an open circuit. First confirm voltage at the bulb sockets with the brake pedal depressed.

Which wire should be put on bulb case and which one should be out on the bottom button? What ohm scale should I use?

It doesn't matter which probe is on the bulb case. You're looking for less than 10 ohms.

Okay. One of the bulbs tested three and 2.6 on each of the two buttons on the bottom of the bulb. That was with the ohm meter set at 200 scale, whatever that means.

Looks like you're down to the wire between the brake light switch and the brake light sockets. My truck has bullet connectors down below the cowl in both circuits. But I put those in. I don't recall if there were connectors like that when stock. But that would be the first place to look. Maybe that connection came loose (if you have one there.)

Checking voltage at one tail light showed something around 5.9 v to 6 point whatever on one of the little buttons when the tail lights are on.

The other one showed zero volts with the brake light pressed and tail lights on.

So, it seems like the bulbs are okay but I'm getting no juice on the brake light circuit to the tail lights

That wiring diagram I attached to an earlier shows that the brake light circuit gets its power from the headlight switch.

But you've already verified that power is getting to the brake light switch, so don't worry about that.

Okay, let me slither under there and see if I can find any connections. It would be nice if there were some that had come disconnected somehow.

I did? I'll take your word for it. Hahaha!

Here's a markup of the wiring diagram that Bill posted. Should be connectors located under the door hinge pillar or thereabouts. Also back near the taillight housing.

And on a side note, the stoplight switch doesn't care which of the two wires is connected to which of the two pins, right? Since it's a switch all it does is open and close so the order that those two are connected is irrelevant, correct?

Correct. Just like a bulb doesn't care which way you put the ohmmeter probes on it.

I'm going to make a wild guess that the original connection is probably for the tail light and that messy looking bundle of electrical tape is probably the brake wiring.

Am I correct to assume that there will be just one wire running to the brake lights and one wire running to the tail lights?


I assume the fixtures themselves will be grounded to the body or frame or whatever along the way? I guess I could look at that schematic. Hahaha

I'll see what I can figure out with this taped up connection, but it looks like a rewire, similar to what I did for the headlights a few years ago is in my future

Looks like a real professional Restoration job!

Another hack job by the dyslexia impaired previous owner.

Dang jalopies! The fun never ends.

For context, when the truck first came into my care, I discovered that two digits on the title had been transposed. Number three and number four plug wire were transposed, the high beam wire and the power wire on the dimmer switch were transposed.

So who knows what else I will run into whenever I dig a Little deeper on this thing?

Well, I guessed wrong. That crappy electrical tape connection was actually the tail light wire and not the brake wire.

Good grief!

Get a load of this. So I assumed incorrectly that that crappy taped connection was the brake lights circuit so I unwrapped it and then discovered that that was actually the tail light circuit.

So I had to make a quickie repair on that, having already decided that the entire rear half of the vehicle needs to be rewired after looking at all that junk under there.

Anyway all the tugging and yanking and messing around with the wires and connections under there got the brake light circuit working again without having to disconnect or rewire any temporary connections..

So now at some point in the future, hopefully near future but I don't have time with so many other things going on I'm going to run new tail light wires and new brake wires.

And of course the idiot that did this work in the past left no slack in the lines. They're just pulled taut and strung all over the place instead of tucked neatly in the frame rail out of the way of everything else.

So in a way I guess it's good that the brake lights didn't work for me this morning because now it's going to force me to do more work that I don't have time for

Thanks for all your help you guys.

I'm sure I'll be back asking more questions when the Day of Reckoning comes and I decide to run new wiring from the firewall to the tail lights.