Horn & rear lights died at the same time.

[geminusprime]

Both my horn and all of my rear lights except the top 3 running lights died at the same time today. I've looked at all the fuses, none have blown. Haven't done a 12v test from the lights on back, but I did check most of the harnesses, although I'm not sure which ones go to what.

Also, I'm pretty sure I can hear a relay clicking when I try the horn, it just doesn't sound.

Are the cable harnesses color coded across different buses? If so, are there diagrams to indicate which wire goes to what?


I know I can trace out all the wires (and get rid of many I don't need), but if there is a simpler option I'd rather attempt that first.

Bus is a 1997 International 3600 Vista

[geminusprime]

Well problem solved after 3 hours.

Posting a reply to myself just in case someone else has this issue.


I had recently installed a radio under the light monitor above the driver. During installation I removed the light monitor, and had only plugged half the cables back in. This has 4 cable sets - upper left, upper right, lower left, lower right. I had plugged the upper cables in, but not the lower.


The lower cables caused the rear lights to not function.


Here's the weird part - the upper left cable set came loose during the drive, and that caused the left turn signals to fail bus wide AND the horn to stop.


I thought it must have just been a weird quirk. Risking causing more problems, I can replicate the error. Unplug upper left cable set from light monitor, horn doesn't work. Relay clicks, but horn doesn't sound. Cable plugged in, it works.


No clue why the horn is affected by the light monitor, turn signals, and specifically the left ones.




Check your light monitor connections. Because reasons.

[Native]

That sure does sound like a strange setup, at least logically speaking. You may find that you have "customizations" in the wiring.


[Note: I have no experience with any bus but the conventional Thomas ... but your discovery just does not make sence to me either.]

[geminusprime]

Originally Posted by Native

That sure does sound like a strange setup, at least logically speaking. You may find that you have "customizations" in the wiring.


[Note: I have no experience with any bus but the conventional Thomas ... but your discovery just does not make sence to me either.]

Oh I'm fairly sure I have some old Monroe custom wiring in this thing. They also did not remove any of it, only cut the grounds, so all the stock equipment is still in there (except the dvr).


But, the lighting issue alone (not the horn, that's weird) was found to be a solution on schoolbusfleet.com. Appearently it had happened before to bus drivers, and someone suggested checking the connections to the light monitor. No clue if that's aftermarket or a standard option, but it worked for me!