12v Wiring Question

[Les White]

The lightbar on my truck is currently switched thru a relay, it's either on or off. I want to add a second switch that will turn the light bar on with the high beams AND I want to keep the existing switch to turn it on independently. Sort of a driving mode vs. plain lighting mode.

The diagram is what I came up with. My question is related to the area in the yellow circle. Do I need to worry about feeding power back into the relay? What if both switches were on? If either of these is a concern how to I isolate the two circuits? A beefy diode?

 

[noway2]

No, I don't think there is any problem. If both switches are on, you effectively have two paths for the positive terminal to feed the light bar, but it's all the same potential, battery / alternator positive. What would happen is that the current flow would split between the two relays. If the relays don't have one built in, you probably want what is called a fly back diode in reverse polarity across the coils to absorb any inductive kick when they shut off.

 

[rdinatal]

you probably want what is called a fly back diode in reverse polarity across the coils

Check the relays. Most already have a diode built in.

 

[Schattenreiter]

Not sure what you want here. Are you wanting the light bar on anytime the high beams are on or just sometimes when they are on.

If the first then the second switch is unnecessary. Simply send power to a relay for the light bar and switch it with power from the high beams.

If you want it on just sometimes when they are on you already have that and anything else would just be redundant.

Also typically relays are wired so powers enters on pin 30 and exits thru either 87 or 87a depending on whether there is power on 85/86 or not.

If feed back is a concern install a diode in each line to prevent back feed.

 

[Les White]

Not sure what you want here. Are you wanting the light bar on anytime the high beams are on or just sometimes when they are on.

If the first then the second switch is unnecessary. Simply send power to a relay for the light bar and switch it with power from the high beams.

If you want it on just sometimes when they are on you already have that and anything else would just be redundant.

Also typically relays are wired so powers enters on pin 30 and exits thru either 87 or 87a depending on whether there is power on 85/86 or not.

If feed back is a concern install a diode in each line to prevent back feed.

Two switches, two functions. Light bar on, and/or light bar on with high beams.

 

[Sharps40]

Um....I think both can be done with one light bar switch like you prolly got now. Sorta turn on the light bar.....then turn on your headlights and select hi or low beam......though I'm not an electrician seems like you have four options already, light bar no headlights, headlights no light bar, light bar low beam, light bar hi beam..... 🔦

 

[Schattenreiter]

Like I said if you want the light bar on whenever the highbeams are on just use the highbeams to turn on the relay. No need for a separate switch. That way the light bar receives power from the battery and not thru the high beam circuit.

 

[noway2]

Like I said if you want the light bar on whenever the highbeams are on just use the highbeams to turn on the relay. No need for a separate switch. That way the light bar receives power from the battery and not thru the high beam circuit.

The way it’s drawn, the light bar does receive power from the battery, not the high beam circuit. The high beam circuit only energized a relay coil.

 

[Schattenreiter]

I am aware of that but there Is no need for the second relay if he wants the bar on anytime the high beams are on an no need for a second switch if he only wants them on sometimes when the highs are on.

 

[Scsmith42]

I am aware of that but there Is no need for the second relay if he wants the bar on anytime the high beams are on an no need for a second switch if he only wants them on sometimes when the highs are on.

Ditto. Your 3 relay system is unnecessarily complicated.

 

[Les White]

I am aware of that but there Is no need for the second relay if he wants the bar on anytime the high beams are on an no need for a second switch if he only wants them on sometimes when the highs are on.

But I only want the light bar to come on with the high beams when I choose via switch, not all the time. Likewise I want the the light bar on all the time when I chose.

I want the light bar off the rest of the time.

 

[Schattenreiter]

But I only want the light bar to come on with the high beams when I choose via switch, not all the time. Likewise I want the the light bar on all the time when I chose.

I want the light bar off the rest of the time.

Then you already have that. Light bar on a single switch. You want it on you turn it on. You want highs on and bar off turn the switch off.

I am not sure why you need a second switch to do what you can already do.

 

[GoWolfpack]

But I only want the light bar to come on with the high beams when I choose via switch, not all the time. Likewise I want the the light bar on all the time when I chose.

I want the light bar off the rest of the time.

So you want it on some of the time, but off the rest of the time. And not necessarily correlated with any other lights.

You can do that now. With the switch.

 

[phideux]

What the last 2 guys said, one switch, turn it on, turn it off. You wouldn't want to wire in to the highbeams so it is on whenever high beams are on, might not be legal to run an extra light bar on regular roads.

 

[rdinatal]

You wouldn't want to wire in to the highbeams so it is on whenever high beams are on, might not be legal to run an extra light bar on regular roads.

It's not legal. In fact any non-DOT lights must be covered while on the road.
That said, I see it all the time.

 

[Beef15]

Three way switch is how I would do it, one feed constant power, one feed from the high beams, I tapped my indicator wire.
On with high beams is fine if not specifically legal, high beams are illegal if approaching or following within certain distances anyway, not that they stop anyone for that either.

 

[Scsmith42]

One relay, two switches will get you where you want to be. The output from your high beam relay should feed switch a, which in turn goes to the trigger contact on the auxiliary light relay. So if switch A is on on and you turn your brights on, the auxilliaryblightbrelaybis energized. If switch a is off, no auxiliary lights when younhit the high beams.

Switch B is fed by 12v and it’s output also goes to the trigger contact on the auxiliary light relay. So when you turn switch B on the auxiliary light relay is also triggered.

 

[Pack72]

How about using one relay and a single pole double throw (spdt) switch with center off. Wire the switch common to terminal 86 of the relay, and ground terminal 85. Connect one switch terminal to a constant 12v, and the other to the 12v from the high beams. Connect the light bar + to the appropriate relay terminal. Then, if the spdt switch is in the center "off" position the light bar is never on. If the switch is in one "on" position, the relay is energized and the light bar is always on. If the switch is in the other "on" position the relay is only energized if the high beams are on. One switch, one relay.

 

[Scsmith42]

How about using one relay and a single pole double throw (spdt) switch with center off. Wire the switch common to terminal 86 of the relay, and ground terminal 85. Connect one switch terminal to a constant 12v, and the other to the 12v from the high beams. Connect the light bar + to the appropriate relay terminal. Then, if the spdt switch is in the center "off" position the light bar is never on. If the switch is in one "on" position, the relay is energized and the light bar is always on. If the switch is in the other "on" position the relay is only energized if the high beams are on. One switch, one relay.

Great idea!

 

[RetiredUSNChief]

It'll work fine.

And a lot of relays already have diodes across they're coils, though there probably won't be any issues without them anyway.

As wired, if both switches are on, all it means is your Light Bar On switch will keep you light bar on even if your high beans are off.

If consider replacing the two switches with a single 3-position switch, either toggle or rocker as you prefer.

Center position would cut power to the light bar entirely, up position and down position wired for your Light Bar On and Light Bar On w/ High Beams.

 

[nhusa]

Why would someone go to a bar and get a light?
if I’m in a bar I’m ordering a craft beer.
light beer is hydrating while working in the yard or sitting on the deck thinking about working in the yard.