Do I need a Diode?

orange150

orange150

Well-Known Member
Joined
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Location
Fairfax City, VA
I have an aux light spliced into my reverse light circuit. I want to wire in an ON - ON switch, where one position is powered by the reverse light circuit, and the other is an override ON.

Do I need a diode in the harness so I don't back feed the reverse lights when the lights are manually switched on?

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orange150 said:
I have an aux light spliced into my reverse light circuit. I want to wire in an ON - ON switch, where one position is powered by the reverse light circuit, and the other is an override ON.

Do I need a diode in the harness so I don't back feed the reverse lights when the lights are manually switched on?

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Not if you wire it correctly. Are you pulling 12v from the reverse light circuit and 12v from a constant hot and running each through a leg on a SPDT switch?
 
You don't need a diode if you're using a SPDT (ON/ON) switch, where:
* the reverse light circuit is one switch input
* the override power is the other switch input
* the aux light is the switch output

Only one of the inputs would be connected to the light at one time, and the two inputs would not be connected to each other, so a diode would not be necessary unless there is some other condition that you haven't explained.


@shawn: what happened to the bulleted and numbered list formatting?
 
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wire in a relay to to switch the light between the 2 different modes.
 
Now that I've drawn it out.. Do I need an ON-ON? It looks like the pink could just bypass it all together. Basically the reverse circuit is it's own switch, I just want to be able to manually switch that lamp on if need be. I feel like I'm not grasping something here, or I over thought it.

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If you're going to use a relay, you only need an ON/OFF (SPST) switch, because you'd only need to energize the relay during the override, which would connect the AuxLamp through the NORMALLY OPEN relay contact. Else the reverse light can be connected to the NORMALLY CLOSED.
So:
Common relay term to the aux lamp
Normally open term to 12V power for the override
Normally closed term to existing reverse light power

Switch energizes the relay coil during the override.
 
You don't need a relay
 
orange150 said:
Do I not? I figured it was good practice to put an aux light through a relay.
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How many amps does it pull? I'm guessing "not many". Output also not likely to be affected by small changes in voltage.
 
I think the SPDT and on/on and relay talk is over complicating it.

If it were me Id break a hot through a toggler and turn the light on with that.
Then if I "needed" it to automatically come on with the reverse lights Id tap the reverse circuit and insert diode and hit the same light.
The diode would prevent back feeding the reverse lights when you were "just" toggled on.
Done.

Now that said. I wouldnt have it come on with the reverse lights. There will be times you want to back up without lighting the world up. Back up spot lights are the perfect use for one of Fords outiftter switches. If you are backing up and need them just hit the switch. Thats what Id do.
But you can overcomplicate it until your heart is content.
 
Ron said:
I think the SPDT and on/on and relay talk is over complicating it.

If it were me Id break a hot through a toggler and turn the light on with that.
Then if I "needed" it to automatically come on with the reverse lights Id tap the reverse circuit and insert diode and hit the same light.
The diode would prevent back feeding the reverse lights when you were "just" toggled on.
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A SPDT (ON/ON) switch is a simple "A or B" switch, with two positions, 3 terminals. A standard SPST (ON/OFF) toggle switch also has two positions, but 2 terminals.

They look the same, and function the same (two positions). You don't need the diode with the SPDT switch, so it's simpler to wire. The addition of the diode is the unnecessary complication. ;)


But yes, if the switch can handle the current for the light (pretty easy if it's an LED light, most likely), there is no specific need for a relay. A nice looking Carling-style rocker switch (Contura series or whatever) can easily handle a few amps for a LED pod light.
 
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Fabrik8 said:
A SPDT (ON/ON) switch is a simple "A or B" switch, with two positions, 3 terminals. A standard SPST (ON/OFF) toggle switch also has two positions, but 2 terminals.

They look the same, and function the same (two positions). You don't need the diode with the SPDT switch, so it's simpler to wire. The addition of the diode is the unnecessary complication. ;)


But yes, if the switch can handle the current for the light (pretty easy if it's an LED light, most likely), there is no specific need for a relay. A nice looking Carling-style rocker switch (Contura series or whatever) can easily handle a few amps for a LED pod light.
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Different ways to skin a cat and what not...but the reverse lights are at the rear where this light is going. It might be 12” or wire and not getting back in the cab. If I’m painfully honest about myself on my truck I’d never put the diode in just let the reverse lights get a a little back juice when I turn the switch on.

I’d just prefer not to be breaking the factory reverse light circuit
 
Ron said:
Now that said. I wouldnt have it come on with the reverse lights. There will be times you want to back up without lighting the world up. Back up spot lights are the perfect use for one of Fords outiftter switches. If you are backing up and need them just hit the switch. Thats what Id do.
But you can overcomplicate it until your heart is content.
Click to expand...

I use an on/off/on switch for this reason. Aux light on, off, or on with back up lights. Just another way to skin this cat.

Duane
 
I'm wanting to wire up a small light bar to serve as a back up light and work light on the jeep. I want to wire it up to a three position switch that way I can have it on constantly for a work light or come on with the factory reverse lights or off so it doesn't come on at all.
My question which way is correct way to wire it.
Option 1
uploadfromtaptalk1362173577248.jpg


Option 2
IMAG0498.jpg
 
Keith1138 said:
I'm wanting to wire up a small light bar to serve as a back up light and work light on the jeep. I want to wire it up to a three position switch that way I can have it on constantly for a work light or come on with the factory reverse lights or off so it doesn't come on at all.
My question which way is correct way to wire it.
Option 1
View attachment 367010

Option 2
View attachment 367011
Click to expand...
87a should be hot when switch power is off allowing you to switch light on and off at will
FBE98852-00FF-49C9-9CF7-7ED5111EDB63.gif
 
Blkvoodoo said:
87a should be hot when switch power is off allowing you to switch light on and off at will
View attachment 367027
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So 87 and 87a both need to be powered according to option 2 or 87a and 30 according to the first diagram.

Then i also found the following in a youtube video
Relay:
Light bar--> 87
Switch-->86
Ground--> pin 85
Battery--> pin 30

Switch:
Switch on 12v--> 8
Ground-->7
Relay trigger 86--> center on switch
Brake light-->3

I have no idea what to trust.
 
Y'all confused the crap out of me. I have my reverse lights on a toggle. They are wired to the standard circuit. Along with the stock feed I spliced a hot wire from a separate toggle. This wire is on a circuit breaker just to protect it.
It's just a LED grommet truck light. Four to be exact. Two on each tail light circuit.
When I'm parked I just flip the toggle.

I dunno why it has to be anymore complicated.
 
Keith1138 said:
I'm wanting to wire up a small light bar to serve as a back up light and work light on the jeep. I want to wire it up to a three position switch that way I can have it on constantly for a work light or come on with the factory reverse lights or off so it doesn't come on at all.
My question which way is correct way to wire it.
Option 1
View attachment 367010

Option 2
View attachment 367011
Click to expand...

I did option 1 on my truck and on my trailer. No diode on the reverse light circuit though.

WARRIORWELDING said:
Y'all confused the crap out of me. I have my reverse lights on a toggle. They are wired to the standard circuit. Along with the stock feed I spliced a hot wire from a separate toggle. This wire is on a circuit breaker just to protect it.
It's just a LED grommet truck light. Four to be exact. Two on each tail light circuit.
When I'm parked I just flip the toggle.

I dunno why it has to be anymore complicated.
Click to expand...

That's fine if you're only want to turn on the reverse lights, but if you want a separate light to come on both with OR without the reverse lights then you would need something like Keith posted. On my truck I have a light mounted on the headache rack that I can use as a cargo light (in which case I wouldn't need the reverse lights on) and I wired it to come on with the reverse lights if I want it to.

Duane
 
On-off-on or DPST will both work. The DPST is more like an A/B switch. Feed constant hot to one leg and the reverse circuit to the other. Which switch you use depends on whether you want the option to have them "off" no matter what else is going on. The lights on our trailer are wired up with a DPST (no relay, but you could have one if the loads required it).

orange150 said:
Both running through the relay using a diode
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Diodes are not required. "Option 1" is the better way to go.
 
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