Help! Double Horn Wiring on ‘38 Plymouth P6

[minnesnowta]

Hello all! Finishing up on installing a whole new wiring harness on a 1938 Plymouth P6 Deluxe.

Problem is, it is has the special-option dual horns, and the wiring diagram is vague at best as to how they should be connected. Right now they work — but too much. They blare continuously every time the battery is Hooked up. 
 

 

does anyone have a P6 who could send in a photo of how their dual horns look? Or ideas as to where we could find a better wiring diagram? Thanks to all!!

Edited February 8, 2021 by minnesnowta

[greg g]

Basically the horn is wired battery to relay, relay to horn, relay to ground through the steering column to the horn button when the relay is grounded it powers the horn.  When most folks redo their horn with the add on button from the parts store they bypass the relay and go power to switch to horn.  The relay can be powered from a couple of places depending if you want the horn to be available with ignition on or IGN off.  If you want horn on regardless of ignition switch you can power the relay from the neg battery terminal or the gang of wires on the battery side of the starter.  If you want it only with IGN on you can get power from the back of the ammeter of the acc terminal of the IGN switch. If your car's has the coil that fits through the firewall you could pick up power from the negative coil terminal.  Also if you are still 6 volt the horns are high load so the wire from the relay to the horn terminals and the wire from power to relay should be 12 gauge wire.

[minnesnowta]

11 hours ago, greg g said:

Basically the horn is wired battery to relay, relay to horn, relay to ground through the steering column to the horn button when the relay is grounded it powers the horn.  When most folks redo their horn with the add on button from the parts store they bypass the relay and go power to switch to horn.  The relay can be powered from a couple of places depending if you want the horn to be available with ignition on or IGN off.  If you want horn on regardless of ignition switch you can power the relay from the neg battery terminal or the gang of wires on the battery side of the starter.  If you want it only with IGN on you can get power from the back of the ammeter of the acc terminal of the IGN switch. If your car's has the coil that fits through the firewall you could pick up power from the negative coil terminal.  Also if you are still 6 volt the horns are high load so the wire from the relay to the horn terminals and the wire from power to relay should be 12 gauge wire.

sir, thank you so much for taking the time to help! In this situation I also have that dang wire coming from the ammeter. Should I just ground that to the relay? 

[Merle Coggins]

When I look at the markings on your picture I see that a wire from "the starter" is connected directly to the horns. This wire is likely a battery HOT and would power on the horns as soon as the battery is connected, as you mention. This wire should probably be connected to one of the relay terminals. 

 

The wire in your hand is labeled "to horn switch" on one end and "to ammeter" on the other end, which is also connected to the horns. This wire makes no sense to me. 

 

The other wires (unmarked) that are connected to the horns seem to connect together and are not connected to anything. I believe these wires to be the horn activation wires that should also be connected to one of the terminals on the relay. This "Y" wire assembly should be the ONLY wires connected to the horns. 

 

Your relay probably has 3 terminals. The 3rd terminal should be connected to the horn wire that goes into your steering column. 

 

I don't have a diagram of how your relay terminals are laid out, but most horn relays with 3 terminals have a power feed (battery hot), an output (horn wires), and a ground (to the horn button). I found this generic diagram on the web, but it should be very similar to your setup. 

 

[greg g]

Now that the schematic is up you can decide how you want to wire.  Think of the relay as a two circuit remote controlled switch. And the circuits as switch (loamp, low demand) and power, (high load and hi demand) you are engaging the high load through a magnetically triggered assembly. For the magnetic switch to work it needs power from the battery or the ign switch and ground, the horn button or the after market switch. The button completes the ground and switches on the magnet.  In the power circuit the switch makes the connection inside the relay from battery through horns to ground.  So the relay sits there in neutral, till you connect the ground through the horn button or the aftermarket switch. This style relay needs to be mounted insulated from the sheet metal as it relies on the ground connection to be remotely connected.  The power from the relay to the horns is self grounding through the horn mounts.  So use the schematic to redo the factory style as long as your relay is known good.

 

As always with 6v stout wires and clean tight connections and grounds are necessary for proper performance.  Note that the schematic shows negative ground so make your necessary connections for positive ground.

Edited February 9, 2021 by greg g