Horn Relay Question

Don't know a thing about this particular circuit but NORMALLY in any electric circuit the hot is interrupted/made by the switch. A ground is never interrupted. However, it is Italian so I guess anything is possible...

 

If the relay "clicks" when the horn button is pushed, the circuit should be ok to the relay. Measure the voltage at the output side of the relay, with the horn button pushed, if it's ok there, then measure voltage at the horn with the button pushed , If the voltage is low or non-existent at the horn, your problem is between the relay and the horn. Probably corrosion on a connector. As a last resort, you can always run a separate wire from the relay, if necessary.

 

Your horn relay shouldn't even have an 87A terminal -- it should be the ...113 relay type. The way it's supposed to work (per the schematic -- but you can switch terminals 30 & 87 and terminals 85 & 86 and it would still work OK):

terminal 30 = a big white wire = always +12V (if the horn fuse and fusebox are OK)

terminal 87 = a big red wire = goes to the "+" side of the horn compressor motor

terminal 85 = small white wires = always +12V (no fuse)

terminal 86 = a small black wire = gets connected to ground when you push the horn button (which closes the relay connecting terminals 30 & 87 together).

Since your relay "clicks" when the horn button is pressed, this shows that everything is OK with terminals 85 & 86. Measure the voltage on the big white wire of terminal 30 (with the horn button pressed) -- if it's not +12V, you most likely have a problem in the fuse/fuseblock area. If it is +12V, follow spiderseeker's advice of "Measure the voltage at the output side of the relay (terminal 87), with the horn button pushed, if it's ok there, then measure voltage at the horn (big red wire) with the button pushed".

 

I wasn't clear in my description -- are you measuring the voltage on the large white wire of terminal 30 when the relay is in place and the horn button is pressed? If you have a bad, high resistance connection upstream in a circuit (like at the fuse/fuseblock), the voltage at a downstream point can measure OK when the current is 0, but it will drop when the current is not 0. An easier way to get access (without having the relay in place) is to use a jumper wire to directly connect the 30 female terminal in the relay socket to the 87 female terminal in the relay socket (if all was OK, your horn would sound ) -- this gives more access to make the voltage measurement when the 30-to-87 connection is in place (i.e., when the current isn't 0).

 

Keep in mind that the fuse which powers the relay and that which runs the horn are different. So it's possible that the circuit running the coil on the relay has power and the circuit passing through the "switch" of the relay to the horn doesn't have power. Check the fuse and power all the way to the horn.

Also, check the ground on the horn.

Jonathan

 

It never is

First thing you might try is to carefully check/match the wire colors & connections at the fuses on the schematic to your car -- (you'll be lucky if it is this easy , but) perhaps some wires got switched around.

Were your radiator fans also not working? Your schematic (Euro 308QV) shows that that large +12V "battery" wire going to the top of the horn fuse is also bridged over by the fuseblock to the two fuses to the right that run the radiator fans -- or do you have a lot of obvious non-stock "wiring modifications"?

 

You can also use Solid State Relays and get rid of the antiquated mechanical contact relays.

See NTE Electronics at www.nteinc.com

There is a wide range of these SSR's and in many earier Ferrari's these would be great to replace the unreliable analog relays.

They are offered in a variety of capacities and trigger voltages.

Take a look at them.

They are fantastic.

I have used an RS#-1010-51 which is a 10 Amp DC model for car stereo amplifiers but the lower rated units can be used for almost everything including radiator fans, etc.

There is no mechanical click or arcing.

 

Sounds like you've got a bit of "sorting" to do