Horn issues

[ThinkBig]

This kinda blows. Pun intended.
I replaced the air horn switch because the old one was leaking air. When I installed the new switch, one wire connector immediately starts to burn and the horn stays on. I tried switching the wires and it doesn’t work at all.
Heres what I’ve done so far.

Both wires are labeled 25 and are identical. There is no designation on the solenoid for + or -
I checked each wire to ground and did not find a direct short. Then I placed the probes in both wires and pushed the horn button and 24v switches off and on appropriately.

It looks like the wires should be interchangeable, right.

I have ave zero desire to burn a wiring harness. What am I missing? This is such a simple thing. What the heck.

The new solenoid does look like a slightly updated model but is supposedly for M35. I also ohmed the old and new solenoids and both have the exact resistance between the terminals.

 

[papakb]

The way the horns work in most MVs is the 24 volts is always on one terminal when the master light switch is in the service brake or service drive positions sending power to the horn all the time. The second wire on the horn goes through the steering column to the horn button and when you push it it grounds that lead and the horn sounds. Check for voltage on one wire and connect that to the horn. The horn shouldn't sound. If it does then there is a short in the horn itself. If you then short the other terminal to ground the horn should sound. If this is working correctly and the horn comes on continuously when you connect the second wire you have a short either in the wire going up through the steering column or the horn button itself is shorted.

Sometimes you can crimp splice a new wire onto the end of the old horn lead and pull it up through the column but if there's rust or crud in the column all you can do is pull out as much of the old cable that you can and use a 5.56 cleaning rod to push out the rest. A good shot of WD-40 helps loosen things up. After you get the wire out use your cleaning rod on a drill to clean out the column and put a healthy dose of a good silicon lube on the new cable when you pull it in.

 

[ThinkBig]

There is one wire when placed on one of the terminals that will make tho horn sound (the other wire is disconnected). So yes, there is one wire that will make the horn blow constantly.
If I move that wire to the other terminal, it shorts.

Does it it sound like I have a faulty solenoid then? Other than leaking air for a few seconds at start up, the horn was electrically fine.

Thank you for your guidance

 

[papakb]

It sounds like the solenoids coil is shorted to ground to me. The wire that sounds the horn when attached must be the 24V hot lead. This would cause the horn to sound if the other terminal was shorted to ground and also would explain why it would short the system when connected to the other terminal. If you have a multimeter with a resistance scale you can use it to measure between the solenoids terminals and ground. Because of the low resistance of the solenoid coil you will get a low reading from either terminal if one of them is shorted to ground as I suspect.