M35a2 horn solenoid

[mitchsc0tt0]

Hey all,
Recently had my air horn solenoid die. Checked all. Wires and verified ground was closing correctly with horn button and hot 24v at other wire. Problem is as soon as I plug in the hot wire it goes on even if I don't plug in the horn button wire from the column. I played around with it and it seems to be grounding to the brass fittings it this normal or a bad unit?

Thanks,

Mitch

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[cattlerepairman]

As you found out, the horn solenoid gets a permanently hot +24V supply and the circuit is completed by closing the ground via the horn button. If the ground wire is disconnected on the solenoid and the horn starts blaring as soon as you put the 24V lead on, the solenoid is grounding itself to the chassis - which it shouldn't be doing!
A replacement would fix that; if you are so inclined you can open the old one and see if you can fix whatever is causing the short.

If the horn blares when both connectors (Ground and 24V) are connected, the cause could also be a chafed horn wire in the steering column, most often where it exits at the bottom (where a rubber plug should be but often isn't), or a short in the horn button itself.

Wiring diagrams are in TM 9-2320-209-20-2-2

 

[glcaines]

If the horn blows when you haven't connected the wire from the horn button, the problem is almost certainly the relay.

 

[mitchsc0tt0]

Thanks all yeah it was a bad solenoid I got shipped to me.

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[jasonjc]

Mine stuck on the other day. Used some BP blaster air tool conditioner. Free it right up.

 

[3rdmdqm]

So in disassembling my horn solenoid to clean it, I of course dropped it and everything flew out before I could note how everything went. Can someone advise on the correct sequence of how this goes back together? There is a silver cylinder, one end has a small hole in it which I believe the small spring goes into, the other end has a rubber end which I assume goes to the air side to block air when not engaged? There were 2 washers, where do these washers go? One on either side of the small cylinder or both on the end of the brass fitting that has a nipple? The washers are the exact size hole for that nipple but doesn’t make sense to have two on there? Any help appreciated.

 

[WillWagner]

If nobody chimes in, I can go pull one out of the parts pile, disassemble and take pics. That won't be until Tuesday though.

 

[3rdmdqm]

That would be fantastic, thank you! I’m not even sure those two washers go inside it or not or if there is another piece that should have been in there that got lost in the drop. Thank you so much for your help.

 

[G744]

No relay used in tactical air horn setups...

 

[WillWagner]

This one is assembled exactly like yours is showing minus the washers. Hope this helps.

 

[3rdmdqm]

Yes, thank you so much! This explains everything, I couldn't figure out what the washers would be for or what possible purpose they had and why they were there. Probably explains the bizarre resonating noise the horns had. Thank you sir!

 

[KN6KXR]

I've been down this road. After some failures I installed an SMC 1/2" 24VDC solenoid. Then I ditched the stock horn and put in a "mini tug" air horn. So much better now! I think it all cost me about $200 but kids are always waving at me to blow the horn for them and when they jump and giggle and stuff it's totally money well spent.