Proper (secondary Horn Wiring?

[zoiberg137]

Ok so I guess this isn't VW specific, but all the same, I want to make sure I'm doing it right. I'm trying to install a secondary horn (an ooga horn, naturally) and am using a relay. See my picture below....the only thing I don't get is how to wire the secondary horn button/switch. One wire goes to the relay...but where does the other one go? When I googled this, some diagrams show it going to ground (but why, when the relay is already grounded?) and some show it going into the positive wire from battery (but why, when the relay is already wired to the battery?)

I guess I'm not just asking where the other switch wire goes...but why! haha

[mukluk]

For relays such as you have in your diagram, the numbered terminals have specific purposes. Terminals 85 and 86 are for the relay control -- they are the positive and negative terminals for a solenoid that mechanically positions contacts inside the relay that will make or break the connection between terminal 30 and terminals 87 or 87a (if used). The solenoid terminals aren't necessarily polarity specific, but the most common setup has terminal 85 providing the ground leg of the circuit and 86 providing the power leg of the circuit. Either leg can be switched to control the relay. In the case of your diagram, 85 is hard wired to ground and the horn button serves as the switch element to control the power coming into terminal 86, thus controlling the relay switching on and off -- the wire to the left of the horn button in the diagram would be connected to a fused power source. Terminal 30 is the power source which will power the actual component (or load) that the relay is controlling and should also have a fuse between the power source and relay to protect that circuit. Terminal 87 is the "normally open" contact of the relay, meaning no power will pass through the relay from terminal 30 while the relay is not powered on via the 85/86 control solenoid. Not shown in your diagram but often present on these relays would be terminal 87a which is the "normally closed" output contact, meaning terminal 30 is connected to 87a when the relay is not powered. When you activate the relay control solenoid by closing the contacts in the horn button, thus providing power to terminal 86, and with the hard wired ground to terminal 85, the relay solenoid disconnects the contacts between terminals 30 and 87a and connects the contacts between terminals 30 and 87 -- thus providing power to the horn as shown in your diagram.
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1960 Ragtop w/Semaphores "Inga"

[mukluk]

This page has a couple decent pictures and simple diagrams to help understand relay circuits a bit better: http://www.sourceresearch.com/newsletter/Automotive-Relays-and-How-They-Works.cfm?emART
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1960 Ragtop w/Semaphores "Inga"

[zoiberg137]

Thank you! Got it wired up and working.

So, since my button wire is on the far left of the diagram is going to a fused power source, and terminal 30 is going to a fused power source, I wired both of these wires together into the same in-line fuse which is then wired into the same hot wire coming from the battery (actually I think its coming from the fuse box, so its double fused, but whatever).

Unless someone tells me its wrong, I'd have to assume its the right way to do it. The horn works, its fused and relayed, all is well. If anyone in the future is feeling as confused as I was and would like a "corrected" diagram, feel free to message me and I'll post it.

[kreemoweet]

Relays are normally used where one wants a small current/load to control a much larger current/load. In such a case, the wire
sizes would usually be very different and so would the corresponding fuse ratings. Putting both the control and the main load
on the same circuit will certainly work, but it also seems rather pointless.
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