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Old 12-07-2022, 08:04 PM #1
joshik joshik is offline
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12v Wiring Sanity Check

I have a small switch panel that feeds relays to a few offroad lights. I have a master arm switch (switch 2 in drawing) in which feeds 12v (when on) to the other switches to power the relays.

I wanted to wire in a bypass in which my high beams bypasses (switch 1 in the drawing) the master arm switch and feeds 12v to switch panel. That way, I can run my offroad lights and turn them on/off with my highbeams.

I was thinking to put a relay between high beam (+) and switch panel so that when I engage the master arm switch it doesnt turn on my high beams.

Just wanted to get a sanity check to see if my logic is sound. Everything will be fused of course.

Some scenarios I was thinking of were these:

1. master arm is off. High beam is on so it engages the relay and provides 12v to other switches.
2. master arm is on. High beam is off. Master arm feeds 12v to switches but does not go back towards the high beams bc the relay is "off"
3. master arm on, high beam on, 12v coming from both sources but that should be ok since its from the same 12v source...?
please exclude the crude mspaint drawing :P
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2003 4Runner Limited 4wd V8. JBA UCA, Dobinsons MRA Front Coilovers, Dobinsons MRA Long Travel rear. Cooper AT3 XLT 285/70R17

91 Ext Cab 4x4 Yota, black with 4" front IFS trailmaster lift, 3" Downey rear springs, Downey Rubicon extended shackles, and 2" body lift. 35" BFG M/T w/ 4.56. Centerforce II clutch, Rancho 5000s all around and Rancho traction bar, K&N Air filter, Flowmaster, ARB Rear Diff Air Locker, Custom "Mad Eyes" light covers, Extended Diff Breathers, Hella Vision Plus Headlights. [SOLD]

Last edited by joshik; 12-07-2022 at 08:07 PM.
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Old 12-08-2022, 10:37 AM #2
aemravan aemravan is offline
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I'm not electrician.. but I THINK you could more properly accomplish what you're after by excluding the relay feeding from your highbeams and just replacing it with a diode so that you can't back-feed voltage from your ARM switch up to your highbeam..... right?

with the setup as you have drawn up.. yes, theoretically the voltage source is the same, but in reality, there will always be a differential in actual voltage which will cause a potential, and I"m not saying you'll blow anything up.. but doesn't seem to be the correct way with having voltages potentially backfeeding.

-with a diode in place of the relay, with your highbeam on, that same 12v source can pass to the panel with switch 2 off.
-With switch 2 on and highbeams off, you would power the panel and the diode would keep the 12v from backfeeding the high beams
-with both on (first of all, what is the scenario that would require both to be on?) I would think just to be on a safe side you would need to look into either installing another diode to keep the backfeed from happening from the highbeams, or, possibly come up with a relay circuit that cuts off the feed from the ARM switch (if on) when the highbeams are triggers .. but it's too early for me to rationalize that right now lol
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Old 12-08-2022, 11:42 AM #3
joshik joshik is offline
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Quote:
Originally Posted by aemravan View Post
I'm not electrician.. but I THINK you could more properly accomplish what you're after by excluding the relay feeding from your highbeams and just replacing it with a diode so that you can't back-feed voltage from your ARM switch up to your highbeam..... right?

with the setup as you have drawn up.. yes, theoretically the voltage source is the same, but in reality, there will always be a differential in actual voltage which will cause a potential, and I"m not saying you'll blow anything up.. but doesn't seem to be the correct way with having voltages potentially backfeeding.

-with a diode in place of the relay, with your highbeam on, that same 12v source can pass to the panel with switch 2 off.
-With switch 2 on and highbeams off, you would power the panel and the diode would keep the 12v from backfeeding the high beams
-with both on (first of all, what is the scenario that would require both to be on?) I would think just to be on a safe side you would need to look into either installing another diode to keep the backfeed from happening from the highbeams, or, possibly come up with a relay circuit that cuts off the feed from the ARM switch (if on) when the highbeams are triggers .. but it's too early for me to rationalize that right now lol
Thanks for the reply! I did look into using a diode between the high beam and the switch panel but it seems that diodes always have a small voltage leak... at least the crappy ones from Amazon did. I tested a few and they did have a small voltage leak. I figured a relay would fix that issue of backfeeding into the highbeams.

So in the scenario of either or on, it should be pretty straight forward. The scenario of BOTH on was a just in case I did so by mistake. There is no use case for it. I was just trying to think of all scenarios and protect myself.

But you are right, either paths could have slightly different voltages due to various voltage drops, however minor it may be.... Definitely something to think about. I may go the route of coming up with some way to have one path cancel the other out if both were to ever be engaged. I might be over
thinking it and some good diodes would prob do the trick huh?
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91 Ext Cab 4x4 Yota, black with 4" front IFS trailmaster lift, 3" Downey rear springs, Downey Rubicon extended shackles, and 2" body lift. 35" BFG M/T w/ 4.56. Centerforce II clutch, Rancho 5000s all around and Rancho traction bar, K&N Air filter, Flowmaster, ARB Rear Diff Air Locker, Custom "Mad Eyes" light covers, Extended Diff Breathers, Hella Vision Plus Headlights. [SOLD]
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Old 12-08-2022, 12:48 PM #4
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Another scenario which I am thinking about is to have my GMRS radio which has it's (+) straight from the battery (fused of course). It turns on using a relay that is triggered by the ignition on. However, when wheeling, sometimes i don't want the radio to turn off when I turn the car off. I was thinking of having a switch to enable the radio to be on even when the car is off.

In this scenario I don't see the issue of two separate paths from the same power source and having varying voltages due to voltage drops along the different paths. The 12v is coming from the same wire but splits off just at the relay and then combines after the relay. Looks to be sound....

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91 Ext Cab 4x4 Yota, black with 4" front IFS trailmaster lift, 3" Downey rear springs, Downey Rubicon extended shackles, and 2" body lift. 35" BFG M/T w/ 4.56. Centerforce II clutch, Rancho 5000s all around and Rancho traction bar, K&N Air filter, Flowmaster, ARB Rear Diff Air Locker, Custom "Mad Eyes" light covers, Extended Diff Breathers, Hella Vision Plus Headlights. [SOLD]
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Old 12-08-2022, 01:22 PM #5
joshik joshik is offline
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Quote:
Originally Posted by joshik View Post
Thanks for the reply! I did look into using a diode between the high beam and the switch panel but it seems that diodes always have a small voltage leak... at least the crappy ones from Amazon did. I tested a few and they did have a small voltage leak. I figured a relay would fix that issue of backfeeding into the highbeams.

So in the scenario of either or on, it should be pretty straight forward. The scenario of BOTH on was a just in case I did so by mistake. There is no use case for it. I was just trying to think of all scenarios and protect myself.

But you are right, either paths could have slightly different voltages due to various voltage drops, however minor it may be.... Definitely something to think about. I may go the route of coming up with some way to have one path cancel the other out if both were to ever be engaged. I might be over
thinking it and some good diodes would prob do the trick huh?
ok, i think i figured out my master arm vs high beam scenario by using a 5pin SPDT. The master arm will be on the NC side and the bypass will be on the NO side and the high beam will trigger the bypass circuit.

reminder, the light switches are just triggering relays for the lights. The load of the lights are not running through the switch

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2003 4Runner Limited 4wd V8. JBA UCA, Dobinsons MRA Front Coilovers, Dobinsons MRA Long Travel rear. Cooper AT3 XLT 285/70R17

91 Ext Cab 4x4 Yota, black with 4" front IFS trailmaster lift, 3" Downey rear springs, Downey Rubicon extended shackles, and 2" body lift. 35" BFG M/T w/ 4.56. Centerforce II clutch, Rancho 5000s all around and Rancho traction bar, K&N Air filter, Flowmaster, ARB Rear Diff Air Locker, Custom "Mad Eyes" light covers, Extended Diff Breathers, Hella Vision Plus Headlights. [SOLD]
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