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Topic: Help !!!!!!!!!!!!! (Read 1408 times) previous topic - next topic

Help !!!!!!!!!!!!!

I have a problem with an exotic car. THE HORN. Now i know some will say hay RENZO you are the Man and WTF. So here goes. This car was completely restored and brought to us for some minor issues. I repaired them all except the HORN. The Horn is a FIAMM air horn from the factory. But here is the issue!!!!!!!!!!!!!! The horn is blown by the signal light handle. Push it in and it is how it BLOWS. BUT GET THIS!!!! The horn lead has a ground on it when not pushed. When you push it to activate the horn the Ground is removed. WTF. So i need a circuit to make this work. Please feel free to post anything you could think of that will work. I think 2 5 pr0ng relays will do it. Suggestions anyone!!!
I spend money I don't have, To build  cars I don't need, To impress people I don't know

HAVE YOU DRIVEN A FORD LATELY!!

Help !!!!!!!!!!!!!

Reply #1 –
The simplest solution is

X

It pretty much requires the horn to only work with the ignition on to prevent excessive draw and melted relays.

But up until about 20 yeas ago, Euro exotics and pretty much anything British liked to use circuits that rely on switching things on and off by diverting ground away from larger loads, changing what the path of least resistance was.  I can come up with these, but they make my head hurt and conjure images of British Leylands going up in flames.

Help !!!!!!!!!!!!!

Reply #2 –
That looks good. It is what i was thinking but simpler. I would think a better system would have been designed for a 4 Million dollar car!!!
I spend money I don't have, To build  cars I don't need, To impress people I don't know

HAVE YOU DRIVEN A FORD LATELY!!

Help !!!!!!!!!!!!!

Reply #3 –
im pretty sure the customer may want the horn to work on a hot at all times ckt.,,, may be the better option incase of a state inspection especially if it is considered "updated" or "compliant" to todays basic safety codes.

Help !!!!!!!!!!!!!

Reply #4 –
Problem is, where are you going to get a NO switch to replace a NC one?  Tom, it would be most helpful if we knew exactly what you were working on.  That way, perhaps original diagrams can be found.  It's the internet, after all.

Help !!!!!!!!!!!!!

Reply #6 –
Ok it is a MASERATI 350 GT 1967 ALLOY only 16 made and no prints were drawn up. And the car was just bought for 4 MILLION DOLLARS!!!!!! jay believe me nothing cn be changed in this car as it is worth a fortune. But the horn got messed up during the restoration. And they contacted me to repair it. So with no prints i am stuck as to how it was originally built. Other than contacting the other 15 owners!!!


http://www.conceptcarz.com/view/photo/492919,16795/1966-Lamborghini-350GT_photo.aspx
I spend money I don't have, To build  cars I don't need, To impress people I don't know

HAVE YOU DRIVEN A FORD LATELY!!

Help !!!!!!!!!!!!!

Reply #7 –
Here is what i have. The Horn pump compressor is grounded to the frame and has direct battery feeding it, So it blows constantly. I found the lead that comes from the TOOTER handle. Another words the signal light handle that when pushed in removes the ground in stead of applying the ground. So without any prints i am assuming it had a relay at one point. And it has to be connected to switched battery in my thinking with a relay control that holds the ground off untill you push in the horn lever and drop the relay as FOE posted correctly. but without anyinfo i am stuck as there is no PRINTS for this car. Thanks Tom

I did find a lead under the dash that was cut and spliced to a different color at the steering column. I am willing to bet you might be right about you theory FOE of a grounded device
I spend money I don't have, To build  cars I don't need, To impress people I don't know

HAVE YOU DRIVEN A FORD LATELY!!

Help !!!!!!!!!!!!!

Reply #9 –
You say, the horn compressor runs all the time. Is there some kind of an air diverter valve that stops the air from going through the horn?
If so removing the ground by pushing the horn button could de-energize the valve, allowing the air to go through the horn.

Help !!!!!!!!!!!!!

Reply #10 –
I think trinom has the right idea.
Would you need a resister to + on the horn button wire to make the gate go HI (plus) instead of floating when the button is pushed?
 

Help !!!!!!!!!!!!!

Reply #11 –
I was thinking about P channel MOSFET and pull-up resistor (~10k) for gate. The switch should be also connected to gate.

R2 isn't mandatory, but it reduces the initial current to gate when the switch is triggered. I would suggest using IRF4905 as a good idiot proof P channel mosfet for high currents. Also don't forget to add antiparallel diode to the horn compressor. Antiparallel means, that it's connected in oposite direction, as the current normally flows - anode should be connected to ground and cathode to the live end. 6 - 10 A diode should be fine.