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post #1 of 21 (permalink) Old 08-26-2019, 04:22 AM Thread Starter
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Aux lights on dual circuit help

I have a set of Baja Design Squadrons in my front bumper that are powered via my Switch-Proís at the moment which allows me to have them on or strobe. I would like also to be able to use them switched with main beam as the headlights are so poor. Been thinking about it for a while.

So am thinking it is basically two independent circuits to the lights. So can I use a DPDT (on-off-on) switch to achieve this? If so anyone know how I need to connect the switch (six terminals).


Secondarily, but similarly, I have rear fog lights. These are wired to conform with our construction and use regs that require them to be switchable but only operate when headlights are on. So they are wired through a relay on that circuit. Iíd like to have them on a separate circuit from the Switch Pro so they can be used on the strobe or flash functions.
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post #2 of 21 (permalink) Old 08-26-2019, 06:37 AM Thread Starter
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Re: Aux lights on dual circuit help

I’m thinking a DPDT switch would work for both front and rear combined. (Of course I could use two SPDT switches but one is neater).

So the circuits front and rear would either be via the switch Pro’s or via the headlight trigger relay, which is how I’d use it, strobes front and rear on together or using with headlights only.


Edit:
Sorry realise that I’ve linked 2 and 5 but they would be the outputs to the two circuits and separate (drawn as one circuit)
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post #3 of 21 (permalink) Old 08-28-2019, 06:29 AM Thread Starter
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Re: Aux lights on dual circuit help

So I think this is the correct circuitry....

Corrected...with some more digging and help from Baz I think Iím there. Switching the neg main beam feed to a positive and connecting it.

The DPDT switch is rated at 25A so I haveít added another relay to the lights which are 6A total. But I might do so.
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post #4 of 21 (permalink) Old 08-30-2019, 12:04 AM
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Re: Aux lights on dual circuit help

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ZerosFJ previously said: View Post
So I think this is the correct circuitry....

Corrected...with some more digging and help from Baz I think I’m there. Switching the neg main beam feed to a positive and connecting it.

The DPDT switch is rated at 25A so I have’t added another relay to the lights which are 6A total. But I might do so.
Sarah -
I don't think that's going to work, at least not according to the '07 schematic, which is all I have access to at this moment. I know that you do have a '14, but I think the headlight circuit is the same for both model years. (I do have the '10+ schematics, but they are on another PC.)

The blue-with-red-stripe wire is the B+ source for the high beams, so connecting that to one end of the relay coil (terminal 85) is correct. But you have the other end of the relay coil (terminal 86) connected directly to the battery (B+), so when the high beams are on both ends of the coil are at the same potential, and no current will flow. You need to tie terminal 86 to ground, not to terminal 30, so when B+ is applied to the coil via the high-beam supply (blue-with-red-stripe), current will flow through the coil to ground and cause the relay contacts to close. Terminal 30 stays connected directly to battery B+ as the current source for your lights.

Hope that makes sense ..
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post #5 of 21 (permalink) Old 08-30-2019, 01:18 AM Thread Starter
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Re: Aux lights on dual circuit help

Thanks @FJtest Yes that makes sense and was how I started but then I was told the high beam is negatively switched and I needed to wire this way round to convert the neg signal to a positive output for the aux lights.

I’ll check again

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post #6 of 21 (permalink) Old 08-30-2019, 01:52 AM Thread Starter
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Re: Aux lights on dual circuit help

This is why I’ve not done this to date...every article I read offers up a different method to tap the hi beam... latest one taps both the headlight common and hi beam (relay connections: 85 to common, 86 to hi, 30 to ground and 87 output) but this would mean the aux lights being powered from the headlight circuit which I don’t like, unless I add a second relay to power the lights....

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post #7 of 21 (permalink) Old 08-30-2019, 05:20 AM
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Re: Aux lights on dual circuit help

I played with this same problem wiring my light bar to come on with high beam with a bypass switch.

I'm assuming you've got DRLs?

If you're still using the Halogen bulbs (not sure on all aftermarket options) The two filaments share a ground and are not isolated. The relay takes much less switching amperage than the two sets of filaments in series can carry, so your AUX lights will come on with the parking lights or DRL, but go off once you power on the low beam at the stalk, as the bulbs now have a direct path to ground that doesn't pass through the DRL resistor.
Removing the DRL resistor (not sure you can do that in the UK) won't fix this either.

I've not got around to it, but you'll have to add an isolation relay to your hi-beam signal.
I planned to switch the contacts in my DRL relay and add a DPST relay to that slot so you now have a NC contact on that relay. This won't affect normal function.

THEN I'll add the second isolation relay, switched from this new DRL NC signal, to interrupt the feedback from the high beam circuit in all cases except when the high beams are actually on (and not just backfeeding through the bulb. Even my Hikari LED's will backfeed some and glow if the bypass circuit is on).
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Last edited by RDTCU; 08-30-2019 at 05:38 AM.
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post #8 of 21 (permalink) Old 08-30-2019, 07:49 AM
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Re: Aux lights on dual circuit help

Quote:
ZerosFJ previously said: View Post
This is why Iíve not done this to date...every article I read offers up a different method to tap the hi beam... latest one taps both the headlight common and hi beam (relay connections: 85 to common, 86 to hi, 30 to ground and 87 output) but this would mean the aux lights being powered from the headlight circuit which I donít like, unless I add a second relay to power the lights....
Sarah -

A few comments:
1. In my proposed circuit, the AUX lights would NOT be "powered" by the high-beam circuit - they would be powered directly from battery B+, as shown in your sketch. The headlight high-beam circuit would only serve to trigger the relay coil, which draws only a few hundred milliamps.

2. The headlight circuit is not "negatively switched"; the power is switched at the B+ supply via the HEAD relay and the DIM relays ("high-side" switching). There is a another relay (DRL relay) in the "ground" circuit, but that only switches a resistor in and out of the circuit to provide reduced current in the DRL mode; the "common" terminal from the headlamps (blue wire) is always connected to ground.

The schematic in the FSM can be a little confusing as it shows the wiring for BOTH vehicles equipped with DRL (wires identified with "*1") and w/o DRL (wiring identified with "*2"). Additionally, the bulb terminals are identified with numerals 1 and 2 (no asterisk, no parentheses), so that can be a bit misleading.
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post #9 of 21 (permalink) Old 08-30-2019, 08:00 AM
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Re: Aux lights on dual circuit help

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Sarah -
There is a another relay (DRL relay) in the "ground" circuit, but that only switches a resistor in and out of the circuit to provide reduced current in the DRL mode; the "common" terminal from the headlamps (blue wire) is always connected to ground.
A little more detail on my experience:

The DRL relay is what throws a kink in the works for what we are trying to do.
If the DRL's are on (automatically when the car is in gear), the low beam circuit is powered, and grounded through the DRL resistor.

Since the low and high beam filaments share a ground, this would cause it to back-feed enough current through the high-beam filaments and the new relay coil to trigger the AUX lights, if the new switch was on the "come on with high beams" setting.

If headlights are turned on at the stalk, the bulbs get full ground (not through the DRL resistor) and then the new relay coil won't see enough current to trigger until the headlights are switched to high beam.
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post #10 of 21 (permalink) Old 08-30-2019, 11:24 AM
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Re: Aux lights on dual circuit help

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RDTCU previously said: View Post
A little more detail on my experience:

The DRL relay is what throws a kink in the works for what we are trying to do.
If the DRL's are on (automatically when the car is in gear), the low beam circuit is powered, and grounded through the DRL resistor.

Since the low and high beam filaments share a ground, this would cause it to back-feed enough current through the high-beam filaments and the new relay coil to trigger the AUX lights, if the new switch was on the "come on with high beams" setting.

If headlights are turned on at the stalk, the bulbs get full ground (not through the DRL resistor) and then the new relay coil won't see enough current to trigger until the headlights are switched to high beam.
Possibly so, depending on the actual resistance of the DRL resistor, the "cold" resistance of the high-beam filament, and the current required to "pull-in" (or "pick-up") the new relay for the aux lights.

Did you try adding a low-value resistor in series with the relay coil? The typical automotive relay will actually pull-in at well under 12V, like around 8V. You should be able to select a value for the series resistor that will not allow the "leakage current" from the high beam filament to trip the relay, but will reliably trip the relay when the full 12V is applied when the high beams are turned on. A typical 12V automotive relay with a 35A contact rating will have a "cold" coil resistance of around 70 ohms; with a 13V applied to the coil, the coil current will be around 180 milliamps.

Alternately, you might be able to select a relay with a higher current rating that, since it has larger, more massive contacts, has a coil that requires more current to pull-in, and the leakage current isn't enough to trip it.
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