Need help with horn after 12 volt conversion

[Richard Cope]

HI,

Recently converted my 39 Plymouth to 12 volt negative ground, used a 12 volt generator, Ron Francis panel & the original style cloth covered wire under the hood.  Happy with the conversion, however have one hiccup with the horn.  Goal is to eventually use the 6 volt trumpet horns with reducers, however to be cautious connected a new 12 volt replacement horn and 12 v. relay to the stock horn bracket, which is grounded.  Ran a positive wire to the relay and  connected the horn wire - negative.  At this time only connected one 12 v. horn.  When the car isn't running or at a low rpm horn works, however after driving for 10 min or so in which the generator is putting out more amps the horn stops working, has a 30A, which doesn't get blown.  Appears that it is overheating, for after awhile with engine off the horn will start working again.  This weekend plan to work with it, does the wiring sound correct?  If so, perhaps the horn & or relay are defective.  

 

As always, thank everyone for your comments,

 

Regards,

Richard

[Sniper]

not sure if this helps, but I am still running the original horns on my 51 without an issue been over a year. since I converted to 12v.  But I think the only time my horn ever gets used is for the annual inspection.  Not a big horn user here.  I think I would check for voltage at the horn when it's not working and go from there.

Edited January 14, 2021 by Sniper
more detail to clarify

[Tooljunkie]

No reason why horn would stop working,as it should take up to 15 volts without issue. 
either its wired incorrectly or there is a a fault in one of the 3 components, horn, switch or relay. A jumper wire and a test light are all that is necessary to troubleshoot. 
 

the horn may be malfunctioning due to heat in the engine bay. 
 

i also used my 6 volt horns and relay after i converted to 12 volts.

[Dan Hiebert]

Your wiring sounds correct.  Most likely an issue with the relay.  It may not be playing nice with the generator's increase in output.  Overheating as you note.  Still, recheck all your connections, especially ensure grounds are clean.  As Sniper recommended, check voltage working from the device back to the source when it isn't working.  Wouldn't hurt to check it when it is working, too.  You may find a voltage drop that will help isolate just where the problem is when it isn't working.

 

I used the original 6v horns in a Ford F3 that had been converted to 12v for years.  They were much louder, I wouldn't call that an issue, but otherwise no issues.

[Pete]

HI Richard,

 

Just a thought: I recently rebuilt the two horns on my 1939 P8. I had them powder coated. The power coat looks great, but is thick enough to kill the ground circuit. I could heard the relay working, but no toot. I added a couple of ground wires from the horn through screws to a bolt securing the bracket to the firewall. Problem solved. Horns as loud as a tug boat. You might want to use your VOM to check continuity to check the ground circuit from the horn hardware to the firewall.

 

Pete

 

[Dartgame]

This sounds like a heat issue. Not knowing where your horns are located on a 39, is it possible they are inside the engine bay above the engine or other source of heat ? If so, then perhaps they get too hot after the engine runs a while and then once cooled off, the horns start working again.

 

My 52 has trumpet horns mounted in front of the radiator core support, and work fine on 12 v., loud as he__ but no problem with them otherwise.

[greg g]

Hey Pete how much would you charge to rebuild another pair???  Currently I only have one that works. I think it's the longer bass gorn and the treble is in operative.  Have filed the points and tried other adjustments and put 12v to it to no avail. Don't need the powder coating, just the honk...

[Richard Cope]

Thank everyone for your comments.  Saturday will have help to press the horn ring to get a voltage reading, suspect that it is either a defective 12 volt relay or replacement horn.  A little concerned about my wiring, for the horns I followed the same wiring diagram as original.  The wire going from the horn ring to the relay is now negative ground as it was originally, and the relay is getting positive power from the voltage regulator which used to be negative.  The horn bracket is grounded to the body which is now negative.  Because of this, should I be wiring up the relay different?  I believe most cars today the wire coming from the horn ring would be positive.  I doubt if it is heat from the engine causing a problem, when I took it for a 30 min  test drive it was 40 degrees outside and still had the hood side panels off.  For those that are using 6 v horns with 12 v. systems, are you using 12 v relays?   I agree powder coating is the way to go, had mine done years ago and still look like new.  Have ground wires attached to the brass screws in the rear of horns that connects  to the horn mechanism and attaches to the firewall, my grounds are good.  Located a supplier that sells a powder that matches the steering column, emergency brake, etc really close for the 39 Ply.  Purchased a pound or so  for around $40 and a local shop coates parts as  I get them ready.  If interested, will pass on the supplier's name and part number.  They give free small metal tags of the color. 

[Tooljunkie]

Horn ring provides a ground. So,positive to control side of relay,and other side of control circuit goes to horn ring. 
pos to switch side of relay, other side of switch goes to horn,then horn is grounded completing circuit. 
the horn and relay are two circuits,one is control, other is load.  

[SteveR]

It shouldn't make a difference if it is negitive or positive ground. It is only a simple circuit. Switches and a coil. It sounds like you are missing a complete circuit when things get hot. I would make sure all grounding is clean and no paint or rust.

 

I hooked up my single horn to 12 vdc and had no problems, but I do not need a relay since it is a single horn.

 

When your horn stops working Check the voltage to the relay coil - no voltage check horn button and follow it back.

Check the voltage at the coil on the horn. No voltage - check voltage at relay to horn. no voltage - check the relay coil using ohms setting. no reading? bad coil.

 

Good luck

[Richard Cope]

Thank everyone for your help, problem solved.  Turned out to be the new 12 volt horn that was using to test before putting the 6 volts back on.  The horn worked most of the time and would then stop for no obvious reason.   Mounted the original 6 volt horns with a 12 volt relay, works good but as everyone mentioned very loud.  End up disconnecting one horn, to quite it down a little.  Unfortunately the trumpet horns don't have the same sound with 12 volts.  Have an idea like to get comments on.  When starting this project I purchased a voltage reducer from Vintage Auto (HR02) which is intended for heater blower motors - 100 watts.   End up putting a new 12 v motor in the heater and didn't use.  If the reducer was mounted under the horn bracket & connected to a 6 volt horn relay with the two 6 v trumpet horns, think it may bring them back towards the original sound?  Attaching some photos of my 12 volt conversion, still have a few small parts to reattach.  Generator is about 1/8 in longer, voltage regulator is a little larger.  The aluminum cylinder near the steering column is a remote fill for the master cylinder.  Panel box is mounted behind the front seat and normally covered with a tarp.  The front load panel seemed to be more flexible than a prewired.  Added a crash relay,  battery

monitor / charger is to the right.

Once again than everyone for your comments,

Regards Richard

[Dan Heston]

After my 12v conversion on my 51 Coronet, I had lots of blown fuses when I used the stock horns.  I finally wired in a 6v drop to the horns and it works great now.  Shouldn't have mattered but that's what I had to do to get mine to work.