Lights on the back of the bus aren't working.

[lawful-nervous]

TL;DR: The lights on the back of the bus aren't working, and we don't know how to tackle the awful rats nest that is the bus wiring. Any advice on how to trouble shoot it would be super helpful.

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We're having issues with our bus electrical. We removed the flashers on the front of the bus and the three identification lamps on the front and back (working on replacing those. Didn't know we legally needed them). The back flashers we left on to convert into an extra set of break/turn lights.

Since removing those, none of the lights on the back of the bus work. We can't get any kind of voltage or amperage reading on our multimeter. But the front lights are still working just fine.

Neither of us are electricians and we can't figure out what's going wrong. Our best guess is that we screwed up a ground somewhere.

The bus is a 1996 Thomas international. I managed to get ahold of the electrical schematics (contacted Thomas' support line and told them our bus make and model), but the wiring is a terrible rats nets---all the labels are decaying and illegible and instead of a conduit, the harnesses are held together with electrical tape.... Any advice?

[musigenesis]

It's possible your rear lights all shared a common return wire, so cutting the return to the ID lamps killed everything back there. Try grounding the return wire from one of your lights that isn't working (i.e. connect it to the bus body somewhere) to see if this is the case.

And kudos for calling them identification lamps! Everybody calls them clearance lights.

[magnakansas]

where are you?

if you are anywhere near me I might be able to come over and help sort out the mess.

all of the buses I have worked on.. use the body of the bus as the ground... The exception to this is the fiberglass shuttle buses.

william

[DeMac]

After your fifth post, please add some photos of the rear bulkhead wires.

Do you have a test light or meter to verify you have ground or hot or neither?

Look for a cut common ground. Probably a white wire, definitely screwed into the bulkhead's sheet metal framing.

[rossvtaylor]

Originally Posted by musigenesis

And kudos for calling them identification lamps! Everybody calls them clearance lights.

Very true and accurate..but I learned them as Michigan lights.

[lawful-nervous]

Originally Posted by musigenesis

It's possible your rear lights all shared a common return wire, so cutting the return to the ID lamps killed everything back there. Try grounding the return wire from one of your lights that isn't working (i.e. connect it to the bus body somewhere) to see if this is the case.

And kudos for calling them identification lamps! Everybody calls them clearance lights.

Thanks! I'll try that.

[lawful-nervous]

Originally Posted by magnakansas

where are you?

if you are anywhere near me I might be able to come over and help sort out the mess.

all of the buses I have worked on.. use the body of the bus as the ground... The exception to this is the fiberglass shuttle buses.

william

I'm in Ohio, up near Michigan. Send me a PM if you're near by. We would love to have your help!

[ewo1]

Originally Posted by lawful-nervous

TL;DR: The lights on the back of the bus aren't working, and we don't know how to tackle the awful rats nest that is the bus wiring. Any advice on how to trouble shoot it would be super helpful.

---

We're having issues with our bus electrical. We removed the flashers on the front of the bus and the three identification lamps on the front and back (working on replacing those. Didn't know we legally needed them). The back flashers we left on to convert into an extra set of break/turn lights.

Since removing those, none of the lights on the back of the bus work. We can't get any kind of voltage or amperage reading on our multimeter. But the front lights are still working just fine.

Neither of us are electricians and we can't figure out what's going wrong. Our best guess is that we screwed up a ground somewhere.

The bus is a 1996 Thomas international. I managed to get ahold of the electrical schematics (contacted Thomas' support line and told them our bus make and model), but the wiring is a terrible rats nets---all the labels are decaying and illegible and instead of a conduit, the harnesses are held together with electrical tape.... Any advice?

If you are gonna do any kind of wiring you should have a tone generator. This is used for locating wires within a bundle.

something like this -> Amazon link


It is very simple to use and will help you locate your wires.
I uploaded one of the pages from the file you shared, I believe it is page 5.

You will need to zoom in to see the markup much clearer.

So what you have is 3 wiring circuits. You have the main body circuit which I labeled #1) the "jumper Circuit" which I labeled #2) and finally the end of the cable which I labeled #3).
So #1 should be somewhat easy to locate. Follow the wires from the bottom of the steering column. That should eventually lead you the connector that couples #1 with #2.
Once you find it, unplug it and using either your voltmeter of a test light check the voltages to see if there is voltage present when you turn on the signals or brake light.

I forgot to mention, first check your fuses and also the turn signal relay.

If all is good at connector #1-#2 then reconnect and go towards the back of the bus and locate connector #2-#3. Open it here and again check for proper voltages fluctuation when applying turn signals and brakes.

If all is good here then your last step will be to visually and physically check your grounds, lamp holder and the lamps themselves.
You not gonna have a common ground return wire. all grounds should go right to the metal bus body.

The way to use the tone generator is real easy.

Start from the back of the bus, attached the red wire of the generator to the hot (12v) wire of the stop or turn signal wire, turn it on (the generator not the bus) and using the amplifier/speaker begin to follow the wire that is carrying the tone generator signal forward until you get the the main electrical box.

The tone generator is used for wire locating and nothing else.

Once you located the correct wire bundle and individual wires you can inspect and/or test continuity with your ohmmeter.

While all this might sound overwhelming it really is quite straightforward!

[lawful-nervous]

Thank you so much! I really appreciate you going out of your way to answer this and even marking up the schematics for us!

We have tried using a tracer in the past---an electrician friend came to help us---but it didn't work. We thought the metal body of the bus might have thrown it off. Have you used tracers successfully in a bus before? If so do you have any tips or recommended brands?

Thanks again for being so helpful!!

[ewo1]

Originally Posted by lawful-nervous

Thank you so much! I really appreciate you going out of your way to answer this and even marking up the schematics for us!

We have tried using a tracer in the past---an electrician friend came to help us---but it didn't work. We thought the metal body of the bus might have thrown it off. Have you used tracers successfully in a bus before? If so do you have any tips or recommended brands?

Thanks again for being so helpful!!

This is a decent tracer to have -> https://www.amazon.com/Tracer-Circui...A3QY80NORGXT27 , and it only about $30 bucks

The way to use it is very simple.
You have two leads on the transmitter, red and black.
The circuit you want to trace, disconnect the wire on one end, the work end, and connect the red lead to it.
Black lead goes to chassis.
In the telco world the black lead would go to the second wire so in this scenario the black wire goes to any ground source/chassis, that is our second wire.

The transmitter should have a slide switch either on the outside or maybe you need to remove the cover to find it.

The purpose of the slide switch..-> the transmitter should have two tones. A solid tone and one that oscillates, on to off to on...repeating.

Both tones have a purpose. The oscillating tone is the most common used on and it help to quickly identify a wire within a bundle.
Think of the oscillating tone as a/c signal...meaning it does not produce a flat line signal but one when viewed on an oscilloscope would show a high/low fluctuation. You need to understand this because this is what causes the tone signal to bleed into other wires. To the inexperienced you might think those wires were shorted together somewhere.. but no they are not.

the solid tone is used to without question, identify that one wire you are looking for. It is also helpful in identifying high opens but that is a topic for another day.

Again this is really quite simple, try it a couple of time, you will get the hang of it very quickly.

To answer your question, I have used tome generators ALOT !!!
I own 4 set of them! Why? I got them for free!
They are super simple to fix !