two relays to one switch

Hi All, Forgive the ignorance here, but I'm learning. I'm installing an auxiliary horn (4-tone GM horns) that will be actuated by a momentary switch. These horns will be wired separately from my OEM horn. It's been recommended that I use two relays (1 relay for each pair of horns to maximize power). My question is how should I connect the two relay's power to one switch? Should I simply splice the positive leads from the relays and connect to switch? Attached is a diagram from FireEater over at a Dodge Durango forum. I've been following this. I'm just confused about the connection to the momentary switch, since he connected his horns to the OEM wiring. Again, I will be connecting to a momentary switch that I will install. One other question. Would you recommend a 30 amp fuse for each relay? Thanks for any help.2013 Subaru Outback Limited

2005 Toyota Sequoia

I wouldn't worry about using separate relays for the sake of more power/current. Chances are the wiring will drop more power than the relay, just don't exceed the relay rating. EG three 8A horns on a 30A relay or 4 on a 40A relay should be fine. (Relays should be inductive or motor load rated, but automotive relays usually are.) Besides, if max power was an issue, I'm sure that diagram would have the horn grounds to the battery -ve terminal (maybe in addition to chassis). Taking the relay grounds (85) to the battery -ve is pointless, the chassis will do fine. But otherwise, yes - just join he coil wires somehow ie, 86 to 86. Relays coils are usually less than 250mA and typically ~60mA which is not high current. The fuse must me no higher then the lowest rated link, ie, 40A or less for a 40A relay or 30A if that uses 30A rated wiring etc. PS - IMO the only reason for the two circuits in that diagram - assuming the relay and wiring can handle total current - is redundancy or being able to sound either or both pairs.

oldspark wrote: I wouldn't worry about using separate relays for the sake of more power/current. Chances are the wiring will drop more power than the relay, just don't exceed the relay rating. EG three 8A horns on a 30A relay or 4 on a 40A relay should be fine. (Relays should be inductive or motor load rated, but automotive relays usually are.) Besides, if max power was an issue, I'm sure that diagram would have the horn grounds to the battery -ve terminal (maybe in addition to chassis). Taking the relay grounds (85) to the battery -ve is pointless, the chassis will do fine. But otherwise, yes - just join he coil wires somehow ie, 86 to 86. Relays coils are usually less than 250mA and typically ~60mA which is not high current. The fuse must me no higher then the lowest rated link, ie, 40A or less for a 40A relay or 30A if that uses 30A rated wiring etc. PS - IMO the only reason for the two circuits in that diagram - assuming the relay and wiring can handle total current - is redundancy or being able to sound either or both pairs.

Thanks for your help. This may sound stupid, but is there a way to determine the amperage of each horn? The relays I purchase indicate an amperage of 30/50 (see here). Does this mean they are rated for 30 amps? I plan on wiring with 14 gauge wire. Thanks.2013 Subaru Outback Limited

2005 Toyota Sequoia

Your link doesn't work but I assume it's an SPDT aka changeover or 5-pin relay in which case the higher rating is for the NO (Normally Open) contacts which are the ones you'd be using. The lower rating (ie 30A) is for the NC (normally Closed) contacts since they only have spring pressure to keep them closed - not the stronger force of the solenoid aka coil. The following are a few methods to test current, but unless I had a suitable ammeter I'd probably sacrifice a few fuses. IE - try a 30A, then 20A. then 15, 10, 5A etc until they blow. Note that fuses will blow immediately or quickly only if their rating is greatly exceeded, eg, a 10A fuse will take 10 seconds to blow with a 15A load; 1 sec @ 25A, and hours at 12A.     DO NOT BURN YOURSELF on the fuses, a normally operating fuse may be quite hot, tho normally they should run no worse than warm (eg, normal current should generally be no higher than 70-80% of fuse rating). If I were you I'd probably parallel all horns to the fuse you select for the distribution (ie, wiring & relay) and see if that blows or gets very hot. Then I'd upgrade the wiring or relay if needed rather than running 2 circuits - that's assuming the cost is ok & redundancy etc is not required. Note that the fuses in the circuit posted are NOT to protect the horns- one fuse per horn is required for that, and even then I doubt they can be protected (a bit like LEDs and most single-component loads). Otherwise an ammeter is required to test the current. A DMM or multimeter on 10A range could be used assuming they are less than 10A and don't have too high an inrush current. But they don't look like they'd be over 10A, and DMM 10A ranges are unfused and should handle short peak currents over 10A. TIP - return the DMM test lead to the normal volts-ohms-mA socket as soon as finished with the 10A range. Nothing worse than testing next time on the 20V or other voltage range and wondering why there are sparks and the DMM or tested circuit is smoking, but a 10A shunt (ie, essentially a short circuit) between its -ve & -ve leads will do that! Another method may be to series connect with a 55W or 100W globe etc and connect across a 12V battery. The ratio of their voltages should be the ratio of their currents (eg, 55W => ~4A) but that's only a guide due to non-linearities with lamps etc, but should be good enough to determine if close to 4A, 6A, 15A etc. Could do similar with 2 or 3 series horns to measure their current if your ammeter has limited range. EG - you suspect 20A horns but only have a 10A range, hence insert the 10A meter in series with 2 or 3 series horns whereby the current should be 1/2 or 1/3rd of normal 12V current respectively. That assumes the horns have the same current, but that too can be confirmed with voltage measurement across each. Ask if any of the above need further clarification. Or maybe someone can chime in or search for those horn currents? (What fuse is used for them in OEM vehicles?)

oldspark wrote: Your link doesn't work but I assume it's an SPDT aka changeover or 5-pin relay in which case the higher rating is for the NO (Normally Open) contacts which are the ones you'd be using. The lower rating (ie 30A) is for the NC (normally Closed) contacts since they only have spring pressure to keep them closed - not the stronger force of the solenoid aka coil. The following are a few methods to test current, but unless I had a suitable ammeter I'd probably sacrifice a few fuses. IE - try a 30A, then 20A. then 15, 10, 5A etc until they blow. Note that fuses will blow immediately or quickly only if their rating is greatly exceeded, eg, a 10A fuse will take 10 seconds to blow with a 15A load; 1 sec @ 25A, and hours at 12A.     DO NOT BURN YOURSELF on the fuses, a normally operating fuse may be quite hot, tho normally they should run no worse than warm (eg, normal current should generally be no higher than 70-80% of fuse rating). If I were you I'd probably parallel all horns to the fuse you select for the distribution (ie, wiring & relay) and see if that blows or gets very hot. Then I'd upgrade the wiring or relay if needed rather than running 2 circuits - that's assuming the cost is ok & redundancy etc is not required. Note that the fuses in the circuit posted are NOT to protect the horns- one fuse per horn is required for that, and even then I doubt they can be protected (a bit like LEDs and most single-component loads). Otherwise an ammeter is required to test the current. A DMM or multimeter on 10A range could be used assuming they are less than 10A and don't have too high an inrush current. But they don't look like they'd be over 10A, and DMM 10A ranges are unfused and should handle short peak currents over 10A. TIP - return the DMM test lead to the normal volts-ohms-mA socket as soon as finished with the 10A range. Nothing worse than testing next time on the 20V or other voltage range and wondering why there are sparks and the DMM or tested circuit is smoking, but a 10A shunt (ie, essentially a short circuit) between its -ve & -ve leads will do that! Another method may be to series connect with a 55W or 100W globe etc and connect across a 12V battery. The ratio of their voltages should be the ratio of their currents (eg, 55W => ~4A) but that's only a guide due to non-linearities with lamps etc, but should be good enough to determine if close to 4A, 6A, 15A etc. Could do similar with 2 or 3 series horns to measure their current if your ammeter has limited range. EG - you suspect 20A horns but only have a 10A range, hence insert the 10A meter in series with 2 or 3 series horns whereby the current should be 1/2 or 1/3rd of normal 12V current respectively. That assumes the horns have the same current, but that too can be confirmed with voltage measurement across each. Ask if any of the above need further clarification. Or maybe someone can chime in or search for those horn currents? (What fuse is used for them in OEM vehicles?)

Try this link, please. I will attempt to figure out the amperage with my DMM. By parallel, you mean connect all horns' positive leads (and ground all negative), right? Thanks for you help!2013 Subaru Outback Limited

2005 Toyota Sequoia

That link works in the preview, but not in the post. I'll try it this way. http://www.delcity.net/catalogdetails?item=739802013 Subaru Outback Limited

2005 Toyota Sequoia

This site censors some sites - eg, eBay (read the rules?) - but in such cases an item number or other identifier works (we have the power of google). Yes - parallel is all +ves joined and all negatives joinrd, but just try ONE first on the DMM because in parallel, all the currents add up. (Series is a "string" of + to - to + to - etc in "series". Each components voltage adds to the total voltage (eg, 12V) and the current thru each component is the same.)

Peter I'm the one who suggested two relays. See previous thread. BTW it's pointless, 4 will be no louder than the original pair, simple physics. Here's the original thread:- https://www.the12volt.com/installbay/forum_posts.asp?tid=137098

howie ll wrote: Peter I'm the one who suggested two relays. See previous thread. BTW it's pointless, 4 will be no louder than the original pair, simple physics. Here's the original thread:- https://www.the12volt.com/installbay/forum_posts.asp?tid=137098

What would be pointless?2013 Subaru Outback Limited

2005 Toyota Sequoia

As I pointed out on your previous post, air horns would be far louder, you can feed them from the original horns, just up grade the fuse. With 4 horns, you're giving yourself a mounting/positional nightmare.