car horns wiring 2 pairs 4 horns

Printed From: the12volt.com
Forum Name: Relays
Forum Discription: Relay Diagrams, SPDT Relays, SPST Relays, DPDT Relays, Latching Relays, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=134943
Printed Date: May 14, 2025 at 8:24 AM

Topic: car horns wiring 2 pairs 4 horns

Posted By: askalmaster
Subject: car horns wiring 2 pairs 4 horns
Date Posted: September 26, 2013 at 2:27 AM

DIY plan - car horns for normal and loud use.

pushing the Steering Wheel Horn Button (stock/OEM) will trigger only 1 pair(2 horns) to honk.
pushing the Momentary Push Button (diy in dashboard) will trigger all.. 2 pairs (4 horns) to honk.

not much of an electronic guy so i asked some car forum friends for ideas.

here's some of them.. not been tried/used in real application so i'm not sure what does work.

A.
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B.
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are they right.. possible.?
if yes.. which one is better to use?
Thanx In Advance

Replies:

Posted By: oldspark
Date Posted: September 30, 2013 at 11:46 PM

Electrically they are both the same (as far as I can see) but the top diagram is "conventionally" correct since relay coil 86 should be the more +ve whist 85 is the more -ve or GND - and hence the "old relay" is shown with interchanged 85 & 86 connections.

The above won't matter in practice unless you use relays with internal spike/coil suppression diodes, or if someone expects to see 86 & 85 as +V & -V/GND respectively.

The above can be done with 2 relays - namely the new and old but with a diode from the Mom dash button to old relay GND (should be 85 but is 86 as drawn above); diode line end towards the switch.
Hence MOM grounds BOTH relays but the diode prevents the horn button grounding the new relay.

Posted By: davep.
Date Posted: October 02, 2013 at 4:12 PM

How about a SPST (on/off) toggle switch instead. One side to the existing horns, or #30 of "old relay" in your diagram. Other side of switch to the new horns. The wheel-mounted switch would activate either loudness, depending on switch selection. I live in Los Angeles. I'd just leave it on "loud". Or ship the switch entirely.

My experience is with North America domestics, and the horn wiring and relays are adequate to power an additional set of horns. Imports may be different.