aux lights relay diagram.

I want to wire up some aux lights, and it's a little different than I've done things in the past.

I'd like three modes with a single double throw center off switch.

- Aux lights off. (center)
- Aux lights on (up, ignition on).
- Aux lights on (down,high beams).

Typically, I'd wire the positive side through a switch and to the relay trigger. But in this case, since the switched 12v and headlight 12v are already in the engine compartment, near the relays, near the lights, it seems it might be easier to switch the ground instead, which I've never done before. Does this circuit look like it will work for my purposes?

https://paulor.smugmug.com/Image-Hosting-1/Forums/web/i-QXbw2g4/0/M/relay-diagram-M.jpg

Hmmm... Guess I can't edit my post. That should be Double PULL switch, not Double throw.

Quite correct though two things spring to mind.
You show an SPCO (single pole changeover) switch in the diagram but from what you wrote after I'm sure you're aware.
Second I hope your high beams only come on with the ignition, otherwise that could leave you with high beams and aux lights permanently on unless you remember to turn off that switch (or run the ground side through an ignition controlled relay).

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

And unless the 87a's go to something different, you could use a single relay and feed the hibeam & +12V switched through diodes.
That's just to save a relay and space at the expense of 2 diodes.

But I might use the 2 relays as shown for redundancy - ie, no need to carry a spare relay, the spare is in use and can be swapped upon failure if needed, else the other circuit used and relay replaced whenever convenient.
[ Redundancy can be academic - the difference in reliability between 2 diodes and 1 relay as opposed to 2 relays may be insignificant - or maybe the 2 diodes and relay are more reliable. The question is, when the sole relay fails (hence no aux lights), is it acceptable (until it can be fixed)? Or is it better to be able to use "half" the circuit (with the still-working relay)? ]

howie ll wrote:

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...you show an SPCO (single pole changeover) switch in the diagram ...
Second I hope your high beams only come on with the ignition, otherwise that could leave you with high beams and aux lights permanently on unless you remember to turn off that switch

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Yes, the headlights (hi or low) turn off with the ignition, after an adjustable exit delay. On the diagram, I tried using OmniGraffle for the first time. Gave up trying to find a good relay template, so I built my own, but grabbed a switch diagram from their templates... Should have made that one too!

oldspark wrote:

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...and unless the 87a's go to something different, you could use a single relay and feed the hibeam & +12V switched through diodes.

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Not following how to do this... If I feed both the switched 12V and high beams through diodes into 86, then I would loose my 'switched with high beam' functionality. 87a would be an inverted output, not sure how that would help, but I'm not an expert on relays, which is why I posted here!

Yes you are right. I overlooked the DPST switch...

Ignore my entire last reply.
(Except for the bit about me preferring the 2 relays anyhow, ie, iac pfbz's diagram...)

pfbz]I wrote:

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m not an expert on relays, ...!

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Yeah, right....

You nailed their logic. (And me to a cross!)

Who needs to be an expert? They are either switches or changeover switches, functions to increase current, change current flow or polarity reversal.
As basic units.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

A practiced Expert? Not if self-taught or tutored sufficiently - at least the logic part.


But Howie, the question is, "can an expert be wrong"?


Alas, it's past my bed time.
Goodnight.

Of course we can.
Go back to burying the FB111s in that field.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

I believe this may help..

This is how to set up a three (3) position switch.
One is to have the lights come on automatically when triggered by another power source, ie: reverse lights/parking lights.
Two is off all the time
Three is turn them on independently.

On the Switch

-One side goes to fused ignition power (on the diagram it is written for constant power, not ignition switched.)
-Middle goes to trigger post 86 on relay
-Other side goes to what you want to tap into (ie: reverse lights)

On the Relay

-30 goes to fused 12v power
-86 goes to middle terminal on switch
-85 goes to a ground
-87 goes to Aux Lights

This is the correct Diagram to use with the wires going to where I just mentioned.


These are the switches I used.

https://www.allelectronics.com/make-a-store/item/RS-146/SPDT-CENTER-OFF-ROUND-ROCKER-SWITCH/1.html

To infernicus, thanks for the really nice diagram not being sarcastic I wish I could do them like that.
Also thanks for the link, I've been looking for ages for a switch like that.
BUT Oldspark and myself had already pointed the possibility of one relay and the need for ignition control.


-------------
Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

Yup, Infernicus' setup eliminates the second relay, which is nice.

The downside for me is that I would need to tap the high beam circuit under the hood (near the lights), run it through the firewall to the new switch, and then back out to the relay.

Also with the switched 12V. While I can surely find a switched 12V source under the dash, it's very easy to get the source under the hood near where the relays will be mounted right at the factory power distribution box, without having to vampire into a wire, so another hot lead I need to run through the firewall.

I've always switched the hot leads before (as Infernicus suggests), but thought by switching the grounds I would have a cleaner install, and only have to run a two ground wires from under the dash, through the firewall, and to the front of the truck rather than three hots...

Switch is nice though. I like that it has a round bezel. Much easier to mount cleanly.

howie ll wrote:

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Of course we can.
Go back to burying the FB111s in that field.

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Well Some can Howie

hey come fix my computer



Guess Who?

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No guesses - Howie has left this site.