Help needed! Tail lights not working but brake lights work

[southhillkids]

Please help.
I have a 2010 Thomas built short bus (chevy express 3500)
The brake lights work but the tail lights are not working
Reverse lights and turn signal lights also work
I checked all fuses I could think of
none of them are blown as I can see
not sure if they were working when I bought the bus
only thing I did to the electrical was to unplug the child safety device and a bunch of non working front control boards


any ideas?

Thanks very much!

[TheHubbardBus]

I assume you inspected all the bulbs and the individual filaments within those bulbs (assuming they're incandescent)?

[southhillkids]

Originally Posted by TheHubbardBus

I assume you inspected all the bulbs and the individual filaments within those bulbs (assuming they're incandescent)?

I haven't, but I will
It's not likely both bulbs are out at the same time?

[TheHubbardBus]

I agree it's not the most common scenario, & I generally don't focus on unlikely coincidences first, but sometimes if it's really easy to check something - as would be the case here - it helps just to rule out that possibility up front. FYI I've seen it more than once, and there are a handful of possible causes that might make them go at once (or be noticed at one time, even if they didn't blow simulataneously).

[Kentucky Dreaming]

My first wife had the same symptoms on a 1981 Oldsmobile once.

The culprit was the headlight switch.

The switches have changed drastically since '81, it's something to check if the bulbs are good

[southhillkids]

I opened the light box and found this
please see the attached photo

it says "stop/tail upper"

looks like that single socket connection should be responsible for both brake light (which works) and the tail light (which doesn't work)?

Does this kind of light box have two bulbs inside? One for brake another for tail?

Should I order new light box? It says made by weldon with part number
5801-0100-10

Thanks for your advice!

[TheHubbardBus]

You said your brake lights work. 'stop' is another word for brakes.
Regardless, just replacing parts hoping to stumble upon the source of the problem is a great way to get rid of spare cash, but a poor way to diagnose problems.
Did you ever check the bulbs?
You should buy an inexpensive multi-meter and teach yourself to use it. This won't be the last time you find use for it, I promise.

[southhillkids]

yeah
trying to open the box and check the bulbs now

Originally Posted by TheHubbardBus

You said your brake lights work. 'stop' is another word for brakes.
Regardless, just replacing parts hoping to stumble upon the source of the problem is a great way to get rid of spare cash, but a poor way to diagnose problems.
Did you ever check the bulbs?
You should buy an inexpensive multi-meter and teach yourself to use it. This won't be the last time you find use for it, I promise.

[TheHubbardBus]

Unless something's been bubba'd on that bus, you should access the bulbs by removing the lense from the outside.

[southhillkids]

The front looks like this

I can't seem to separate it from the white plate in the back

Originally Posted by TheHubbardBus

Unless something's been bubba'd on that bus, you should access the bulbs by removing the lense from the outside.

[southhillkids]

I searched online for the part 5801-0100-10
It has a non-serviceable bulb
I can see from the side of the lens that there is only one bulb inside

If the bulb is bad, how come the brake light works but not the tail light?

Is it possible that a bulb is partially bad? Thanks

[TheHubbardBus]

Really. My apologies if my advice was misleading. I didn't know sealed tail lights were a thing. Sorry.


Assuming they're incandescent bulbs, its common for one bulb to serve as both tail and brake. It would have two filaments, and two contacts on the bulb for the two separate circuits (with the metal case of the bulb serving as ground).


I'm not sure what to make of that label. Its kinda standard convention to use wires colored black or brown for the tail light circuit, red for brakes / stop, and white for ground. It looks like you have those as expected, but the tag is confusing. I think its most likely it refers to the functionality of the entire light, but I've been wrong once, so can't say for certain.



Assuming the wiring is as Id expect it to be, If you have a meter, you should be able to test the bulbs without opening the housing (which you can't do anyway). First, remove the connection(s) to the light, then read resistance (ohms) between the terminals on the light (not the harness).. First between red ( stop) and white (ground). Then between black (tail) and white ( ground). If the filament on any given circuit is good, you should get some reading (actual number not important). But if the filament is blown, you'll get a reading of infinity (which may be represented by your meter in different ways depending on what meter you're using).


Again, this only applies to incandescent bulbs. If they're leds this won't work.

[magnakansas]

The bulb has two filaments. One is for brake/turn and one is for running lights. Like having two bulbs in one package. If you want to see how that works. Go to the car parts stores and find a 1157 bulb.

If I were in your shoes, I would shop for a different housing that will fit. One that you can replace bulbs.

William

[southhillkids]

No worries, any advice is appreciated

I found the compatible replacement light with serviceable bulb online

It just puzzles me that this bulb serves as both brake and tail light

but how come only brake light works but not the tail light

again, any thoughts are appreciated

Originally Posted by TheHubbardBus

Really. My apologies if my advice was misleading. I didn't know sealed tail lights were a thing. Sorry.

[magnakansas]

5801-9100 Should be Weldon part. Looks to be a version of yours that you can replace the bulbs. About $25 I found this at Unity school bus parts

William

[southhillkids]

Thanks
That makes me more confident in ordering the new compatible parts with serviceable bulbs
looks like it uses a 3157 bulb

Originally Posted by magnakansas

The bulb has two filaments. One is for brake/turn and one is for running lights. Like having two bulbs in one package. If you want to see how that works. Go to the car parts stores and find a 1157 bulb.

If I were in your shoes, I would shop for a different housing that will fit. One that you can replace bulbs.

William

[southhillkids]

Thanks
you are right

Just ordered the parts

Hopefully this solves the problem and the bus will pass inspection

Originally Posted by magnakansas

5801-9100 Should be Weldon part. Looks to be a version of yours that you can replace the bulbs. About $25 I found this at Unity school bus parts

William

[southhillkids]

Just did the measurements several times and got the same readings

Ground and tail 2.7ohm
Ground and stop/brake 0.6ohm

Same reading on both left and right lights

Any thoughts?

Originally Posted by TheHubbardBus

Really. My apologies if my advice was misleading. I didn't know sealed tail lights were a thing. Sorry.


Assuming they're incandescent bulbs, its common for one bulb to serve as both tail and brake. It would have two filaments, and two contacts on the bulb for the two separate circuits (with the metal case of the bulb serving as ground).


I'm not sure what to make of that label. Its kinda standard convention to use wires colored black or brown for the tail light circuit, red for brakes / stop, and white for ground. It looks like you have those as expected, but the tag is confusing. I think its most likely it refers to the functionality of the entire light, but I've been wrong once, so can't say for certain.



Assuming the wiring is as Id expect it to be, If you have a meter, you should be able to test the bulbs without opening the housing (which you can't do anyway). First, remove the connection(s) to the light, then read resistance (ohms) between the terminals on the light (not the harness).. First between red ( stop) and white (ground). Then between black (tail) and white ( ground). If the filament on any given circuit is good, you should get some reading (actual number not important). But if the filament is blown, you'll get a reading of infinity (which may be represented by your meter in different ways depending on what meter you're using).


Again, this only applies to incandescent bulbs. If they're leds this won't work.

[southhillkids]

I went ahead and measured the voltages in the socket that plugs into the lights

ground and tail reads 0 (this is with all lights turned on manually)
ground and brake read 13.xx v (this is when the brake pedal is pressed)

Looks like the problem is not from the bulbs but somewhere in the bus the circuit between ground and tail is open?

oh well...

Originally Posted by southhillkids

Just did the measurements several times and got the same readings

Ground and tail 2.7ohm
Ground and stop/brake 0.6ohm

Same reading on both left and right lights

Any thoughts?

[magnakansas]

Connect wire to ground to battery negative. Connect wire to stop connect to battery positive. Did the light , light up? Yes- then you have a problem with bus wires.

No then the tail light is bad


William