Electrical Help.

Mac5005

Mac5005

Well-Known Member
Joined
Oct 19, 2005
Location
Rocky Mount
So I’m wiring up some led lights behind the grille on my wife’s 4Runner, and I can’t remember how I did this before on the suburban.

I have an on/off/on switch.

I’m wanting the leds to be able to be switched on all the time, off, or on only when high beams are on.

Have them on the bench at the moment to test the wiring.

First try :

I switched the ground side, and had the normally closed contact on the relay hooked for ground when the switch is in “on all the time position”.

The normally open side of relay was triggered closed when the high beam wire powers the coil side of the relay.

It worked, for the most part.

Turn switch “on” lights come on.

Switch off lights don’t come on regardless of hi beam on/off.

Turn switch to “high on” lights come on/off with the relay trigger ( high beam on/off).

Works as it should. Except:

When switch is in “on” position the leds come one, but turn off when you activate high beams.

I know I can do it with two relays but trying to it with one, and I can’t remember or find a good diagram of how to do so.

Thanks
 
F92421F2-38E4-49F9-BA56-3E216429B7EB.jpeg
 
orange150 said:
Is switch ON bypassing the relay?

Or maybe I'm not reading it right. It looks like 30, 12v from High and switch ON are all on Battery Ground
Click to expand...
Agreed. The relay is in the wrong spot. When it comes in with the headlamps, it's pulling power from the headlamp circuit.
 
New lights should be attached to pin 87, ground should be to the far right side of the switch, headlights go to left side of the switch, center pin goes to 30.
 
shawn said:
Agreed. The relay is in the wrong spot. When it comes in with the headlamps, it's pulling power from the headlamp circuit.
Click to expand...

Switch “on” bypasses the relay. Less than 10a load for these lights. 9.16a @ 12v, 8.2A @ 13.4v.

The high beam wire only powers the coil side of the relay. Minuscule power (.15a or 2.1 watts) consumption to charge the coil.

The high beam headlamp circuit and relay are more than capable of handling an extra 2 watt load to trigger the coil inside the relay.
 
Last edited:
Mac5005 said:
Switch “on” bypasses the relay.
Click to expand...
Why? Seems like a bad idea. The OEM wiring is probably small and not sized for the load. You'll see voltage drop at the lights.
 
As a point of reference, I was getting a 3vdc drop at the cigarette plug at the back of the suburban with a 4A load. 18 ga wire.
 
shawn said:
Why? Seems like a bad idea. The OEM wiring is probably small and not sized for the load. You'll see voltage drop at the lights.
Click to expand...

The switch “on” has nothing to do with factory wiring. The main 12v + power source come straight from battery and fuse holder with 12ga wire to the lights.

The switch is only deciding the path to ground (-) for the lights.

With switch “on” the circuit for the lights is closed directly to ground.

With switch “off” circuit is open.

With switch “on high” , when the high beam headlights are turned on, this 12v (+) triggers the coil of the relay, closing the circuit to ground thru (87 from switch) to (30 to ground)
 
Electricity is not a dead end street. If the lights are grounded through the OEM high beam wiring, they're depending on a small gauge wire for power.
 
orange150 said:
Is there a need for a diode on the switch ON side so it doesn’t back feed the vehicle harness?
Click to expand...

No, not on the forced “on” side.

If the relay were to fail, on the “on w/ high beam” the relay would stay closed despite the coil telling it to disengage when turning off the OEM high beams. This would be due to the contacts essentially arc welding the circuit closed inside the relay.

Relays do pretty well life span wise and the less amperage the better.

At least there will be instant notification as the lights would stay on despite high beams being turned off.

On the manual “on” position the leds are on/off separate from any oem wiring.
 
There's nothing wrong with the schematic. I would use a second relay for LED power, because I generally don't like to pass load current through a switch (unless you know its a good quality switch, not a parts store special), but that's just personal preference. It should work fine as-drawn if the 3 LED lights don't add up to a not of current.

Should be able to re-draw to switch the power instead of the ground if desired, as another option. It's actually simpler to wrap your head around. The common terminal on the switch is connected to the relay coil, with one switch input connected to ign switched power (if desired) and the other switch input connected to the high beams. The relay directly switches the LED power, and the switch only powers the relay coil (not the LED load). Still a single relay. Just an A/OFF/B selector circuit (edit: picture in next post).
 
Last edited:
Shouldn't need anything else if you're using a 3 position SPDT switch (SPDT with center off, so A/OFF/B or (ON)-OFF-(ON) or whatever terminology you prefer). The 12V ignition source can really be whatever you want. Constant battery, ignition switched, headlight switched, running light switched, etc. Whatever you want for functionality.

The switch is doing the logic, instead of using the relay coil and relay terminals like the schematic @Mac5005 drew. Different ways of doing the same thing.

None of the load current goes through the switch in my schematic, only the relay coil current (100mA more/less depending on the type of relay). Also, it's super simple, because that's all it needs to be.

Could use a SPST or SPDT relay, either one will work fine because the relay is just on/off. As long as it is rated for the combined LED load for all the lights, that's all that matters.

relay.jpg
 
Last edited:
Fabrik8 said:
Shouldn't need anything else if you're using a 3 position SPDT switch (SPDT with center off, so A/OFF/B or (ON)-OFF-(ON) or whatever terminology you prefer). The 12V ignition source can really be whatever you want. Constant battery, ignition switched, headlight switched, running light switched, etc. Whatever you want for functionality.

The switch is doing the logic, instead of using the relay coil and relay terminals like the schematic @Mac5005 drew. Different ways of doing the same thing.

None of the load current goes through the switch in my schematic, only the relay coil current (100mA more/less depending on the type of relay). Also, it's super simple, because that's all it needs to be.

Could use a SPST or SPDT relay, either one will work fine because the relay is just on/off. As long as it is rated for the combined LED load for all the lights, that's all that matters.

View attachment 336665
Click to expand...


I like this setup because it's simpler and switching grounds seems like such a euro thing but I'd bet he wanted to tie the high beam + into the relay because the relay will be at the front of the truck where he's tapping into the HI beam wire. Where this can all go wrong is if the truck uses any sort of fancyass pwm lighting circuit.
 
Fabrik8 said:
Shouldn't need anything else if you're using a 3 position SPDT switch (SPDT with center off, so A/OFF/B or (ON)-OFF-(ON) or whatever terminology you prefer). The 12V ignition source can really be whatever you want. Constant battery, ignition switched, headlight switched, running light switched, etc. Whatever you want for functionality.

The switch is doing the logic, instead of using the relay coil and relay terminals like the schematic @Mac5005 drew. Different ways of doing the same thing.

None of the load current goes through the switch in my schematic, only the relay coil current (100mA more/less depending on the type of relay). Also, it's super simple, because that's all it needs to be.

Could use a SPST or SPDT relay, either one will work fine because the relay is just on/off. As long as it is rated for the combined LED load for all the lights, that's all that matters.

View attachment 336665
Click to expand...
This is the correct schematic. Switch things around if the OEM harness is switched ground or switched hot, but all the components are located correctly.
 
Fabrik8 said:
Shouldn't need anything else if you're using a 3 position SPDT switch (SPDT with center off, so A/OFF/B or (ON)-OFF-(ON) or whatever terminology you prefer). The 12V ignition source can really be whatever you want. Constant battery, ignition switched, headlight switched, running light switched, etc. Whatever you want for functionality.

The switch is doing the logic, instead of using the relay coil and relay terminals like the schematic @Mac5005 drew. Different ways of doing the same thing.

None of the load current goes through the switch in my schematic, only the relay coil current (100mA more/less depending on the type of relay). Also, it's super simple, because that's all it needs to be.

Could use a SPST or SPDT relay, either one will work fine because the relay is just on/off. As long as it is rated for the combined LED load for all the lights, that's all that matters.

View attachment 336665
Click to expand...

Yep yep. Only reason I did it the way I did, it made the physical wiring much easier/simpler physically on the 4Runner.
The relay is mounted on the bracket that holds the lights behind the grill. 3 wires (service cord) ran from switch to relay.

One wire from batt with fuse holder to leds, one wire from high beam wire to relay.

The lights add up to 9.18 amps @ 12v, or slightly less at 13.4.

It’s decent switch, nothing special but not bargain bin. Rated for 30a/12v.


Yes I know how to wire conventional 12v + switched, but I’ve had excellent results switching the ground side. Less load on the relays and switches seem to make them last longer.

Just like nearly every domestic oem and aftermarket ECU, switches things with the ground for less load on the switch itself.
 
Helpful thread. Notes taken.
 
Back
Top