Wiring help needed

[AxeAngel]

Hey all,

Trying to wire up some new lights onto the trailer. These lights have two bulbs in each housing. Each bulb is fed with it's own live wire. I am trying to wire in a DPDT switch to allow the following two settings:
position 1 - one bulb on each light on
position 2 - both bulbs on each light on

here is my terrible diagram for what i am trying to do: the issue that i am facing is that i would think that when i select position 1, the current will flow back through the blue wires(used in position 2) and light up all the lights under the schematic that i have laid out. Anyone have any suggestions?

Could i reverse what I am doing and just switch ground instead of power? What is the negative behind that(possible short, etc?), will this lead to battery drain?

Thanks,
Sam

 

[dwh]

Uh...
Okay, looking at the diagram as I type this...

First, you said a DPDT switch, but the diagram shows an SPDT. Not that it matters, you can use a DP as an SP by just not using the terminals on one side.

As for the question about switching the ground: If you do that, and there is a single ground wire for each fixture (as in your diagram) then when you switch the ground off - both lights in the fixture will stop working.


Your diagram works, but with one little problem. I've corrected it. All I did was remove two little unnecessary jumpers. You can see what I changed inside the yellow circles:

 

[dwh]

Oh wait. My bad. You want to have 1 light or both lights. The fix I made to your diagram doesn't do that, it does either/or. Let me take another look...

 

[dwh]

Okay, sorry about that.

First, you need to delete the jumpers like I did in my first pic. Then you need a DPDT switch. Wire it like this:




With the switch in position 1, relay 1 will be energized. With the switch in position 2, both relays will be energized. (Center will be both off - if the switch has a center position.)

 

[AxeAngel]

My bad for not indicating on the circuit the dpdt switch.

My concern in your drawing is that when relay 1 is energized, current will travel back through the blue lines and turn on all the lights(through the connection where you made the yellow circles). Does that make sense?

-Sam

 

[AxeAngel]

Or are you saying each relay controls one bulb in each light and by activating both relays(in position 2) I can achieve the same goal and not worry about "cross wiring"

I think this is what you mean and it make sense.

 

[dwh]

Yup, you got it.

With the jumpers in your first pic (the little blue lines that I deleted inside the yellow circles), you are cross-tying circuit 1 and circuit 2 together - creating a single large circuit. Energizing either relay, would light up all 4 lights.

So you have to separate the two lighting circuits, and then use the switch to select which gets energized.

With the edited drawing with an SPDT switch, what would happen is that in position one, relay 1 would be activated, and in position two, relay 2 would be activated, but there would be no way to do both at the same time.

Which is why I added the wiring diagram for a DPDT switch. Done that way, you can do one/both; but unfortunately, you can't do either/or.

To have the ability to do both either/or and one/both would require adding another switch.


(I should have explained it better yesterday, but I had to run an errand and was in a bit of a rush so I slacked off. )

 

[Truefire]

I do not see why you could not wire it up using the two single throw relays as you have in the diagram but using a three position, Single pole double throw (On -off-On) switch to operate the relays.

Yes by constructing it in this manner you would receive a backflow of electricity to one of the relay's contacts dependent upon which set of lights you are operating. If say for instance switch is in position 1 serving two lights and not all 4. The second relay would have electricity on one side of it's contact, but the contacts are open at that particular relay so it really does no matter, there cannot be any backwards voltage flow across the contacts in the second relay because the contacts are open. The voltage would be only on the load side of the open contact. That electricity would no longer be there the moment you flip the switch across the (off) section to energize all four lights.

So you would never have to worry about this function popping a fuse or as you stated being worried about it being cross-wired, if you will..

The key is ensuring you use a single pole, double throw (on-off-on) switch...

Chris

 

[dwh]

I do not see why you could not wire it up using the two single throw relays as you have in the diagram but using a three position, Single pole double throw (On -off-On) switch to operate the relays.

I'm not following you. Let's start at the beginning - which diagram are you referring to? His original or my edited version?


EDIT TO ADD:

Okay, now I see what you are saying.


To reiterate what I said in an earlier post:

The problem with his original drawing, is that he has tied all 4 lights together into a single circuit.

At that point, it doesn't matter what you do: If you energize Relay 1 - all 4 lights will come on. If you energize Relay 2 - all 4 lights will come on.

Thus, the little blue jumpers (deleted inside the yellow circles in my edited drawing) MUST be removed in order to split the lights into pairs.

Then, if you use an SPDT switch you will be able to energize either Relay 1, or Relay 2, but never both.

Center off doesn't change that - with an SPDT switch, you get either/or.

But that's not the goal, the goal is one/both, not either/or.

To get one/both you need the DP switch.

 

[pods8]

Couldn't you just separate everything downstream of the relays and do the cross over on the feed to the relay coil (the trigger of the relay)? Use a SPDT switch and have 1 leg go to only one relay, have the other leg got to both relays but put a diode in the line that goes over to the first relay. So in position 1 the current flows to relay 1 and gets stopped by the diode before going to relay 2. In position 2 the current flows to relay 2 and to relay 1 through the diode.

 

[Sheep Shagger]

Is their a need for relays? Ie what's the watt of the bulbs your using and can the switch take that load? You could simply use a diode to stop the back flow. Either way all you need is a diode between the bulbs or between the relays. Either one of these circuits would work.

 

[dwh]

Couldn't you just separate everything downstream of the relays and do the cross over on the feed to the relay coil (the trigger of the relay)? Use a SPDT switch and have 1 leg go to only one relay, have the other leg got to both relays but put a diode in the line that goes over to the first relay. So in position 1 the current flows to relay 1 and gets stopped by the diode before going to relay 2. In position 2 the current flows to relay 2 and to relay 1 through the diode.

Sure, that would work as well.

I wasn't trying to devise alternatives - I just took what he already had, and fixed it so it would work.


From a replacement parts perspective, he might be better off with the relays (easily obtainable) rather than the diode.

 

[dwh]

Is their a need for relays? Ie what's the watt of the bulbs your using and can the switch take that load? You could simply use a diode to stop the back flow. Either way all you need is a diode between the bulbs or between the relays. Either one of these circuits would work.
View attachment 115837

That would also work.

Another thing that would work (in case no one noticed), would be to use my DPDT wiring diagram and just toss the relays and diodes out completely and be done with it.

 

[pods8]

From a replacement parts perspective, he might be better off with the relays (easily obtainable) rather than the diode.

If it was a diode on the coil line it could be a tiny one from radio shack (easy to get to) that usually come in multiples so you could just leave some extras in the rig.

That would also work.

Another thing that would work (in case no one noticed), would be to use my DPDT wiring diagram and just toss the relays and diodes out completely and be done with it.

Yeah I was under the assumption he needed more amps and thus the relay. Del city has some euro style rockers that are 20amp DPDT if that will cover the amperage needed.