safe to wire pin 30 to pin 86?

I want to cut down the number of wires that need to be routed around the dash so I was thinking that on my relays I need a 12v constant to pin 86 and pin 30. Would it be safe to just cut a small piece of insulation from the "pin 30 to 12v constant" wire and solder in the end of the pin 86 wire. Pin 30 and 86 would still have a 12v constant and the current draw should be 10amp or below. This would also lower the number of wires that need to be attached to the 12v constant. Which is about 8 at this point lol. Thanks in advance!

Yep - you have just described a common 3-terminal horn relay (common +12V with switched +12V to the horn, and #85 grounded via the horn button). But I would use spade connectors else a relay socket rather than solder the relay terminals.

oldspark wrote: Yep - you have just described a common 3-terminal horn relay (common +12V with switched +12V to the horn, and #85 grounded via the horn button). But I would use spade connectors else a relay socket rather than solder the relay terminals.

Yes I am using a relay socket so i will be soldering the wires for the pins. Thanks for the info btw i forgot to ask ill be using a diode for suppressing the coil voltage spike. Does it matter if the diode is placed before or after the splice for pins 86 & 30?

Normally its across #85 & #86 (line end to the +12V #86) or "as close as possible" merely to reduce antenna length - ie, less change of inductance etc coupling. But since "most" of the spike is electrically conducted, near enough is probably good enough. IE - you want it "between" the coil and the other circuits on that circuit (ie - before the alarm, switch, sensitive equipment). And by "most" I mean "the worst effect" etc... IMO I've given a bad description & explanation! (Maybe others will intercede?)

Don't forget to fuse 30, 86 will be adding at most about 1.5 amps to that load. I prefer to diode across the coil but I have a question, if 86 is constant what is the load being switched at 85? It has to go to ground through a switch. If that switch is say an alarm aux output rather than a physical 12V switch then wire the diode inline to 85, band away from the relay

But that doesn't quench the spike - the spike could then superimpose (travel) on the +12V line. Hence why spike suppressors (diodes) are placed across the source (in parallel). (As opposed to "blocking" diodes that are inline with the signals - ie, in series.) But those reverse-biased diodes across #85 & #86 only quench a negative spike. But that is the coil's reaction to having its current removed - it doesn't matter which end is removed/cut/stopped, only the polarity across the coil matters - ie, Kathode = diode line-end towards the +ve end of the coil. (Yes? Or do I have to reconsider long forgotten (read: assumed or known) things? Grrr!!! IE - series blocking does not quench, it merely blocks, so instead of -200V going that way (ground), the other end becomes +200V... (??).)

Never understood it till I got the shock about 40 years ago, I haven't forgotten. Forget the theory I just use what appears to work.

Hmmm - it would stop the shock at the switch end, but reflect it out the other. But honestly Howard, get with the times - you need to update with more modern experiences..... I posted the shock I got when checking to see if my manual horn button worked. (Due to the horn-ring bush breaking off, I used fingers to short its wire to ground.)    That was a few weeks ago. Very modern indeed! I'd like to say it's nice reinforcing and confirming old lessons.... On 2nd thoughts, stick with older experiences. I'd argue they had better quality anyhow! (Unfortunately for me, freshness is still overriding any thoughts of shock quality. Maybe when I fully recover in a few years...) Besides, with your modern knowledge and long experience, who the heck am I.....

Hey oldspark, Sorry I wasn't clear in my post. But yes I will be placing a diode between the wires for pins 85 and 86. My alarm will be sending a negative trigger to the relays to pin 85. I found a wiring schematic on this site here is the thread https://www.the12volt.com/installbay/forum_posts.asp~TID~86348~PN~2~TPN~2 But since I am splicing pin 86 into 30 I wanted to know if the diode which crosses from pin 86 to pin 85 needs to be before the splice for pins 86 and 30 or after. But you answered that so I will wire the diode in before my splice. howard, yes I will be adding a fuse to the wire from 12v constant to pin 30. I think a 15amp fuse should work well in this application. One relay is for the headlights and another is for the sirens and another for my trunk release. I haven't seen any information about suppressing coil voltage spike so I was just going to wire it based on the diagram in the link I posted above. You need to scroll down to "dualsport's" post to see the diagram. Thanks for your help everyone

It does not matter where it gets put on the wire.  It can be before 30.  I always solder the diode to the base of 85 and 86.  Place the relay on the edge of a table or bench, set the diode on the relay and bend the legs to the appropriate length, solder the legs to 85 and 86, this leaves plenty room to install the connectors to the terminals of the relay.  It makes a neat install and it is more maintenence free than soldering the diode to a wire that is subject to moving.