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spencerin
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# Posted: 7 Feb 2021 02:26pm
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How would I wire an LED light bar so that it turns on only when I flip on my car's high beams, and what impact would it have on the fuse box? Right now I have it wired as intended, where it has its own separate switch.
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pabear89
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# Posted: 7 Feb 2021 03:40pm
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Use a relay to power the light bar.
hook the switch source of the relay to your high beam wire and it will trigger the relay to turn on the light bar when the high beams are on.
Using a relay will be a separate source from fuse box.
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spencerin
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# Posted: 7 Feb 2021 03:52pm - Edited by: spencerin
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I watched a couple of YouTube videos, and they use 3-way switches so that you can turn the light bar on-and-off independently, turn it off altogether, or have it come on only when high beams are on. I just want it to come on only when the high beams are on or turn it off altogether. Under this scenario, it seems like all I need is a piggyback fuse to replace my existing high beam fuse, then I remove the hot wire from the battery, cut it, and wire it to the piggyback fuse. The existing switch I still use to toggle power on-and-off to the light bar - when the switch is off, the light bar is off altogether, and when the switch is on, it allows power to be delivered to the light bar only when the high beams are on. Does that sound right? Is it really that simple?
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razmichael
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# Posted: 7 Feb 2021 04:11pm
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I'm with pabear89 on this - I would use a relay (they are really cheap) and use a separate fuse. It adds a level of separation from the normal high beam system in case something goes wrong. I don't know but powering both systems through the same wiring (even with a larger fuse) could be risky if the wiring was not capable of handling the extra amperage. Basically what you want to do but with a realy so you power the aux lights as you describe directly from the battery with fuse (or elsewhere) but control the relay through smaller, low amp wiring.
If you want the flexibility a three way switch to the relay (two from low power sources) could cover all three scenarios with the common factor being a main power line (with fuse) to the relay and then lights.
1. Auto on when highbeams are turned on (power take off from high beam line through switch to relay)
2. On without the highbeams on through switch to relay from an aux power line, and
3. Off no matter what (no power to relay)
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spencerin
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# Posted: 7 Feb 2021 04:20pm
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I have an existing relay. So, I leave the hot wire from the battery alone, find the hot wire running between the existing switch and relay, cut it, and re-wire it so that it runs between the switch and piggyback fuse?
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Brettny
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# Posted: 7 Feb 2021 04:39pm
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I would also use a relay. There are plenty of visual diagrams online that can explain it better than I can do via text on how to wire it.
If you want to be able to not use the light bar simply put a switch on the coil side of the relay.
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razmichael
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# Posted: 7 Feb 2021 04:45pm
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Simplistic diagram - by "have a relay" I'm assuming you already have one with the current aux lights??
The red lines are what I would do with a 3 way switch. so the lead take-off from the high beams goes to one of the connectors on the switch.
Likely not exactly as your current setup but may help.
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spencerin
Member
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# Posted: 7 Feb 2021 05:07pm
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Yep, using a relay that came with the light bar. Just need confirmation on what adjustment I need to make to it.
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gcrank1
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# Posted: 7 Feb 2021 05:14pm
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Fwiw, You should never cut and tap into the main battery feed wire to hook up accessories.
Many fuse boxes have an unused circuit already there.
Fuses are to protect the wiring, not the device. I suspect that a bunch of the burned up vehicles one sees or hears about had a hacked in accessory.
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razmichael
Member
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# Posted: 7 Feb 2021 05:16pm
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It will be a pretty standard automobile relay so just a matter of the most efficient and safest way to use it.
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paulz
Member
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# Posted: 7 Feb 2021 06:46pm
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All my experience is with old stuff, but those headlight circuits use a self resetting circuit breaker in place of a fuse.
I was riding a motorcycle I had wired on a country road one night when the headlight fuse blew at about 45mph. Pitch black out, couldn't see a thing. Luckily I got it stopped still in the roadway, just about the same time I quit peeing my pants.
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toyota_mdt_tech
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# Posted: 7 Feb 2021 09:42pm - Edited by: toyota_mdt_tech
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Quoting: spencerin How would I wire an LED light bar so that it turns on only when I flip on my car's high beams, and what impact would it have on the fuse box? Right now I have it wired as intended, where it has its own separate switch.
I would use a relay, grab power from battery, with a fuse for the LED light as close to that power source as you can and have your high beam circuit just turn on the relay, so it would work like you want it but not increase the load on the existing circuits.
Those generic relays, 30 is the input, this is power from your battery, 87 is output or power to the LED lamp, then you have the magnetic coil, ie terminal 85 and 86. So if you use power to control the relay, ground one side of the coil and power up other side. If relay is turned on by grounding the circuit, power up one side of the coil and other ground it via switch to control relay.
Many car makers are now grounding circuits with switches to control loads now days. Putting the switch after the load reduces arcing at the switch and makes everything live longer. But the nice thing about the relay is, you can do it either way.
5 pin relay wiring diagram
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pabear89
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# Posted: 8 Feb 2021 10:11am
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Quoting: spencerin I have an existing relay. So, I leave the hot wire from the battery alone, find the hot wire running between the existing switch and relay, cut it, and re-wire it so that it runs between the switch and piggyback fuse?
Take wire from relays switch post 86 and use a bridge connector on one of the high beam light wires and your done.
Hooking a 3 way switch can be done but you must wire it correctly as not to power your high beam lights when you turn on the light bar. The back feed may cause damage.
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