The Stovebolt Site Forums The Shop Area The Electrical Bay 41 tail/brake light problem

Hi Folks,

I bought a replacement tail/brake light for my 41. It's a reproduction of the original and has a green wire and a black wire coming out the back. I hook them up to the original wiring (2 wires) and it didn't work. I reversed the hook up and still not working. How are these wires hooked up? The system is 6 volt/generator, and wiring is original.

Also, where is the brake light switch located?

Thanks,

Jeff

The brake lamp switch is located on the master cyl. under the driver side floor.
It sounds like you have a bad ground. Is the lamp bolted to the truck? If not it won't ground. If it is bolted to the truck, then you have a bad body ground to the frame.

my replacement lights had two wires coming out as well...one was the feed for the brake bulb and one was the feed for the tail bulb. A ground screw was inside for you to run a seperate ground wire. I agree with Toyvo in that it is the ground because the light is not grounded by itself. If you pull the lense off you can put your own ground wire in.

I replaced the ground connection to the inside of the light and connected the other end to the frame. The lights still won't work. I've made sure the connections on the ground wire are good. I had a ground wire connected to the back of the light and the frame before. Is there something else it could be?

Jeff

baldbaron,

Did the light come with the proper 6 volt lamp installed.

The first test would be to make sure your brake/tail wires have power to them, then check the lamp.

The unit might have been dropped in shipping and broken the filament.

Stuart

test power to your wires to ensure you are even getting power back to your light.

Yes, you should always check for power to the lamp first. Did the origional lamp work? I was assuming that it did. If you don't have power to the wires when turned on, do one more check, connect a long wire to the negitive battery post and to your test lamp. Now test for power at the rear lamp. If you have power now you have a ground problem from the battery to the frame.
Lots of people hook up the negative battery cable to an engine or transmission, that is ok but you also need a cable from the engine or transmission to the frame (battery negative to frame). The reason for this is that the engine and transmission are isolated from the frame with rubber mounts, and they may of may not ground. Some ground through the carb linkage or fuel line (if it is metal) if a ground directly to the frame is not attached.

Thanks everyone. I will try the ideas suggested and let folks know if it worked or not.

Jeff

I check the ground and it's from the battery to the frame. There is no power to the lines that go to the tail/brake light. The light switch has power at the tail light connection, and I have headlights and parking lights. I followed the lines from the tail light to a big mess under the gas tank. It appears that someone had a splice party. I'm thinking that I should run new lines from the brake light switch and the tail light connection on the light switch. I'm not sure if the green wire or the black wire from the new light is brake or tail light. Does this make sense, and should I run new lines?

Jeff

Jeff,

A "splice party"! I wouldn't hesitate for a moment to run a couple of new lines. The color isn't important unless you are a purist.

Go back to the nearest switch or terminal and start fresh.

You can attach each wire after you run them to the new taillight. The brightest connection will of course be the the BRAKE circuit.

Judging from your ability to troubleshoot this problem, you DO have some type of meter or tester to verify the presence of voltage...this item would be invaluable as you can't readily see the little electrons dancing around (at the party).

Stuart

Stuart,

Please explain "the brightest connection".

Jeff

Jeff,

I can usually confuse a simple subject. All I meant was that after you run two new wires to your taillight, the correct connection would be self evident when, as the brake was applied, the brightest filament in the bulb was illuminated.

The lamp should be a dual filament bulb. One for tail, one for brake. The brake is a larger, brighter filament. Clear as mud!


Stuart

atomarc, if he has a 41 tail lamp it has 2 bulbs, one park and one stop. it is not dual filiment.

I have the 2 bulb lamp. That's why I was asking about what wire goes to brake and what wire goes to tail light. Also, just so I'm sure, how is the brake light wire run? Does it go to the brake light switch and then to the light switch?

Jeff

Sheesh, two bulbs...what will they think of next!

The brake light switch should have two terminals on it. One side is powered (and fused??) all the time. The other side of the brake light switch goes directly back to the taillight.

Either wire could be brake or tail. The indication of a 'stop' with the taillights on would be the illumination of the second bulb, hence a brighter taillight...WOW.


Stuart

Jeff i'll bet someone has installed turn indicators at one time or another. There should only be 2 wires to the rear of the truck. One from the park lamp switch to the tail lamp and one for the stop lamp. (fused 6V to brake lamp switch and then to the brake lamp.)
Did you do the long wire check? Run a wire from the negative side of the battery all the way to the rear of the truck and use it to ground your test lamp. Then check you wires for power with the test lamp. Do you now have power with the park lamps in the on position? Do you have power with the brake pedal pushed? If no then we most likely have a wiring problem on the power side of the cricuit. If yes you have a ground problem to the frame. (needs a ground from the battery negative to the frame)

In my previous post, I stated either light could be brake or tail..no diff!

This might not be true. Not knowing a darn thing about a '41, I will hazard another guess. The tail light would be the BOTTOM light because it also shines through a small opaque window to illuminate the license plate.

Do this theory hold water, or am I all wet!!

Stuart

that would be correct.

also, get one of those "original shop manuals" off ebay, they have wiring diagrams in them....

Thanks again everyone. My last question I hope. My 41 shop manual shows a fuse at the light switch. My light switch does not have one and it does look like it's old enough to be the correct one. Should I put an in-line fuse on the wire that goes from the light switch to the brake light switch?

Jeff

I wouldn't - the fuse on the switch [may not be recognizeable] is for the primary circuit, and is really meant for the headlights

Bill

baldbaron,

Fuses are always a good idea. The line you are referring to must come off the line, or hot side of the light switch.

The power to the brake lights shouldn't be able to be switched off.

The taillight circuit should also have a fuse...this would probably be the one shown in the shop manual in the original switch.

Stuart

from the shop manual - note the fuse is on the power input from the ammeter - fuses all lights, but the headlights are the primary current draw - fusing rear lights individually will leave you with no lights at the back sometime, with no way for you to know it

Bill

Red the shop manuel is labled wrong.
The diag. for the car and truck are reversed, you can tell cause the truck is labled with 2 tail lamps and a separate license lamp and the car is only showing 1. They just labeled them wrong.
Hey I printed it out, always good to have a schematic.

I didn't even look at the labels, both have the same switch, which is what's under discussion

if you don't have Keith's collection bookmarked, ya should, lotsa good stuff there for handy reference

Bill

baldbaron,

red58 is correct. The picture in the shop manual he linked shows all of the lights protected by a fuse.


Stuart

OK, I'm really confused now. I have headlights and parking lights that work, no fuse and doesn't appear there ever was one with this light switch. Where does the break light wire go on the light switch? Is it a connection that always has power even when the switch is off?

Jeff

balbaron,

The brake light wire goes on the line, or power side of the switch.

This means the switch is AFTER the brake light wire and won't affect it..the switch won't turn it off!

Put a in line fuse in this circuit.

If you have a voltage tester, all this will become a cake walk.

The factory wiring diagram clearly shows a light switch with a fuse included. Yours must have been altered.

Basic wiring, even in '41, included fuses.


Stuart

What amp in-line fuse do I use for the brake light wire? Should I put an in-line fuse on the hot wire to the light switch? If so, what amp fuse?

Jeff

Jeff,

I have enclosed a link that has just the info you need.

I think your brake circuit would do fine with 16 gauge wire and a 5 amp fuse.

I don't know what size wire the original light switch has on it. My guess would be 12 gauge wire with a 20 amp fuse.

If you put a inline fuse holder in the light switch circuit (you should), and it blows fuses under normal nighttime driving, you would need to step up to the next size fuse.

Maybe your shop manual would show light switch fuse size.

http://www.crowbarelectricalparts.com/Specifications.htm

[edit] The '41 shop manual states your truck has a 30 amp fuse. It appears the only fuse on that rig is on the light switch, So I would say that would answer the size question.


Stuart

I have looked all over the master cylinder, but I can't find the stop light switch. I feel stupid, but where is it located?

Jeff

Jeff,

On the later trucks, it isn't ON the master cylinder, it is attached to the bottom side of the floor board/toe board area. The brake pedal arm moves it as you depress the brake.

I don't know if it is this way on a '41 though!

Stuart

I found where it was supposed to be. Someone had removed it from the master cylinder and put a threaded plug in its place. I removed the plug and installed the new stop light switch. I lost brake fluid and as a result have no brake peddle pressure. It goes to the floor now. Can I add brake fluid to regain peddle pressure? How much fluid should I fill the master cylinder with? What type of brake fluid?

Jeff

Fill it and bleed the system.

Jeff,

I sure am learning a lot about '41 trucks!. A hydraulic brake switch...pretty space age for that old beast.

I'm not sure on this, but as long as you only lost fluid within the master cylinder proper, I would bet you could refill it, and by slowly pumping the pedal, get it to self bleed.

I think you want DOT 3 or 4 brake fluid. DON'T use DOT 5 fluid.

Sometimes, you can fill the reservoir at night, and by the next day, it will have 'bubbled' itself to some pedal.

Try the fill and pump routine first, you might get lucky.

Fill it nearly to the top, but lay the cap back on...sometimes they 'spit' at you.

Stuart

Brake fluid should be dot 3 or dot 4. I think thats all you can buy now. If it happens to be girling approved its dot 4.(that means it can be used with natural rubber parts and wont swell the rubber) You don't have to worry about that thow cause only European cars had natural rubber parts.
Fill it to the top of the master cyl. don"t screw the cap back on tight cause you may have to bleed the system and you will need to refill the reservoir.
If you fill it up and still don't have brake pedal after a couple of pumps then loosen the line at the rear of the master cyl. and bleed it there first. You might get lucky and not have to go to each wheel and bleed the system.
Bleeding will require 2 people one to pump the pedal and one to work the wrench. Try this first;
1. full of fluid, push the pedal to the floor and hold it.
2. loosen the line at the master cyl. --- tighten the line at the master cyl. and let the pedal up.
3. repete 1 and 2.
4. repete 1 and 2.
5. repete 1 and 2.
Do you have a pedal now? Did any fluid come out when you loosened the line? If fluid came out and you don't have pedal go to step 6. If no fluid came out are you sure you loosened the line enough? Try #1 and #2 again this time loosen the line more and shake it side to side.
Try it again. And again. No fluid? Remove the line and put you thumb over the hole. Push the pedal Got a squirt after a couple of trys. Hope so. If not you got a master cyl. problem. Replace it and go to step 6.
Before you start step 6 look at your line routing. On most cars, the furtherest point (by following the brake line to each wheel)from the master cyl. to the wheel cyl. is the rt. rear. On your truck it is the lt. rear wheel.
Step 6 can be done with one person, but you need help the first time. Go get someone who likes you to help.
6. Go to the lt. rear wheel, have you pumper pump the pedal --- oh say 4 times and hold it to the floor. loosen -- WAIT!!-- use a small hammer and some penatrant on the bleeder valve, spray it and give it some lite--- LITE!!! taps straight on the end of the valve. Now re-pump and then loosen the valve (hope it don't brake off)--- tighten the valve and pump it again. Do this till you get nothing but fluid. Then re-fill the reservoir. Go to the rt. rear--- do it the same way. Re-fill, now rt. front, and then lt. front. You should have pedal now. If you don't you got other problems in the system, or just stubborn air bubbles. Good luck.

Stuart, I can say that I'm learning about 41's too. This is a first for me for everything, so I appreciate the help from everyone. I will try to get this right. Thanks again folks!

Jeff