Auxiliary Lighting for 2018+ NC750X

CapeMan

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First, some basics ...

In the US, at least, there was a significant change in the NC750X's lighting starting with the 2018 model year, when they went from conventional halogen headlight bulbs to LEDs (Light Emitting Diode). One consequence of this change is that installing dimmable aux lights is more complicated than it used to be.

There's a lot of info elsewhere on this forum about hooking up auxiliary electrical equipment on older NCs and a lot can be learned by reading thru it. But the posts on the 2018+ I've seen (and done) are kind of limited. I thought I should have done better so, in penance, I'm trying to pull together here a thorough summary of what I've learned. Being thorough does mean some redundancy with other posts (sorry about that) but I'd hope that all the info you'll really need to hook up aux lighting might be found here.

Prior to 2018, wiring for the headlights was 12V and there was a readily-available 12V+ signal indicating that the high beam was on so it was easy to interface with available aftermarket lights and controls. Wiring-wise, newer models are somewhat different beasts. One significant difference is that now there's only a 5V+ signal that's only on when the Low Beam is on. And this doesn't work with conventional after-market aux lighting controls.

Other motorcycles might require tapping into the wiring harness and/or soldering onto the headlight plugs to get power and/or control signal for auxiliary lights. Honda has made it a lot easier since they sell an OEM auxiliary wiring harness that provides the necessary connections, complete with connectors. Two parts are needed:
  • P/N 08A70-MJL-D30, “Subharness” costs $16 and consists of a connector that plugs into a connector already on the NC and three connectors that break-out the circuits from the on-bike connector. (Alternatively, you could wire up your own subharness.) EDIT: It seems that not all subharnesses come with plugs that have the same pin locations as the pins found on the bikes' connectors. I have no understanding of why that is the case, maybe a Honda Part Number mystery. If that happens to you, it's really no big deal to reposition the subharness pins in the connector to match those on the bike. There's an extensive discussion of this and some great photos of the process towards the end of this thread: https://www.nc700-forum.com/threads/sub-harness-color-coding-wires.16587/
  • P/N 08A70-MGS-D30, “Relay Kit”, costs $10 and consists of a relay and 7.5 amp fuse that plug into the fuse panel that's to the left of the NC's battery. This relay kit powers up the subharness when the ignition is turned on so it provides switched power.
The installation instructions for these items can be found online as part of the “Accessory Socket” documentation at cdn.powersports.honda.com/documentum/MW01/08E70-MKA-D80.pdf Note: you do not need to buy an Accessory Socket (and you probably shouldn't IMHO, given how limiting that fuse is!) Note also that this relay kit is required as part of the OEM Honda heated grips installation so if you've already got the grips, you've already got the relay kit.

There are 3 connectors to play with once the subharness is installed – 2 of them have 2 wires (brown and green) and one of them has 3 wires (brown, green, and blue). In all cases the green wires are ground and the brown wires are switched 12V+ from the relay and fuse. The blue wire is the 5V+ Lo Beam signal. Matching companion connectors are readily available at cycleterminal.com (an SC110-3 connector will plug into a 2-wire connector and an SC110-4 mates with the 3 wire connector). I'm gonna use the 3-wire connector for the aux lighting; the two 2-wire connectors could be used to supply power for any other purpose, like running a GPS or charging a phone or whatever as long as the total load (including OEM heated grips, if installed) thru the fuse is around 7 amps or less.

I'm gonna suggest an inexpensive roll-your-own control circuit a bit later. But if all you want at this point is to use aftermarket aux lighting Hi/Lo controls and just need a 12V+ High Beam signal, here ya go:

FlopRelay.jpg

The relay you'll need will have to operate on 5V and be either a normally-closed single-throw (so contacts open when coil is powered) or a single-pole double-throw type, which is what I show in the diagram. I'll have a specific relay suggestion further on.

FWIW, Honda's circuit diagram does show one wire on the 2018+ NC that is used to signal Hi Beam. It's a red/black wire from the LED headlight module to the instrument panel, to illuminate the high beam indicator I assume. I've got no data on voltage or polarity in this wire. (In earlier models, this wire is blue and 12V+ on high beam.) I suppose it might be usable for controlling aux lights too but it's anybody's guess. I do know that the relay approach is cheap and simple, works well and doesn't require rooting around in the wiring harness but if anyone knows different, I'd be interested in hearing about it.

PLUS, if you're already prepared to install a relay, you don't really need any expensive aftermarket controls. Just add a cheap manually-set dimmer that will allow you to reduce the aux light output to a level that is comfortable for oncoming drivers, then bypass the dimmer when the bike's high beam is on, something like this:

GenericCircuit.jpg

This circuit is intended to illustrate the concept. While it would probably work in practice, I've shown a “generic” relay and dimmer because the circuit specifics may well call for something a bit different, depending on the dimmer and relay you've got.

For example, I've been using a $9 manually-adjusted Pulse Width Modulation (PWM) LED dimmer (https://www.amazon.com/gp/product/B073YB5NK4/ref=ppx_yo_dt_b_asin_title_o08_s00?ie=UTF8&psc=1) which works just fine but it has an operational aspect that I hadn't anticipated ... it actually passes the 12V+ directly to the aux lights and regulates current flow on the ground, or sink, side of the circuit. I don't know if this is typical for PWM controllers but I wound up with something like this;

Circuit4.jpg

and have been using it for about 8 months now … it's been dead reliable.

Now, I've been a bit coy about the relay specifics so far. In actual fact, I've been using a programmable multi function timer relay – tiny, inexpensive, solid-state, approximately weatherproof, and multi-talented – but I've run on enough here and my lips are getting tired from all this reading. I'll deal with these specifics in my next post, coming right up.
 
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CapeMan

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My Actual Circuit

For a number of years and through several different motorcycles I've been using an inexpensive ($17) user-programmable timer for a variety of purposes (see http://timers.shop/Multi-Functional-3V-18V-Time-Delay-Relay-Timer-5-amp_p_12.html). For example, I've used one to delay power to heated grips until the engine had been running for 10 or 15 seconds and power down when the ignition is off – it's waaay smaller than a conventional relay. Or I have one power a garage door opener remote control for 5 or 6 seconds when the high beam is first turned on – just ride up, flick the high beam on, and the garage door opens up. Sweet!

For my purposes here, I've got M/F-timer-relay powered via the switched 12V+ line and programmed to pass a 12V+ signal only when the 5V+ Lo Beam signal is off. And, BTW, this is all you really need if you're just looking for a “ 12V+ on Hi Beam” signal.

Since the dimmer I'm using works on the sink side, I had to add a $10 “Sink Adapter” (see http://timers.shop/Multi-Functional-Timers_c_15.html) to bypass the PWM. The final $35+ roll-your-own control circuit looks like this;

FinalCircuit.jpg

While it's not shown in this circuit diagram, I do have an on/off switch on the handlebars that can interrupt power to the relay and lights, in case I want to turn 'em off for some reason.

This specific dimmer doesn't look like it's waterproof but it does seem to be fairly well weather-shielded. I've got it stuck to the underside of the cowl inner cover with strong double-sided sticky tape – somewhat sheltered from the elements but I can still (barely) reach the adjustment knob to change the dimmer setting if I need to. The timer-relay and sink adapter are small and nearly weather proof; I just tuck them in next to the battery where they're out of the way.

The multi-function timer relay does have a PWM function but it's not user accessible now. I have suggested to the folks at timers.shop that they add this function and they've been receptive. If they ever get it done, we'd have an all-in-one solution for dirt cheap.

And now it's time to wander way off into the weeds … programming the relay! What follows in the next post will, I hope, be valuable if you ever implement this setup. But if you don't have a specific need, if you don't have a timer-relay and the downloadable users manual in hand, it's probably a waste of your time to read thru, so if that's the case, best just skip my next post.
 
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CapeMan

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You, too, can be a programmer …

As I indicated earlier, the Multi-function timer ( http://timers.shop/Multi-Functional-3V-18V-Time-Delay-Relay-Timer-5-amp_p_12.html) is hugely flexible. It can act as a relay, stopping or relaying power with an “On” signal or of an “Off” signal, suddenly or gradually, with an adjustable delay yada yada yada. All in all, at this writing, there's well over 30 different functions it can be set up to perform.

For our purposes here, and with one significant difference, we want Function #22, the “Follow” function, in which the relay has a 12V+output when and only when the control/trigger line is 5V+. The significant difference is we want just the reverse – output when control/trigger is off and vice versa - but that's OK 'cause a reverse output is also programmable.

So, specifically, we want to configure the relay as “Follow function (#22), reverse output, and high trigger = off”. (This sentence probably seems like gibberish unless you've had a look at the downloadable users manual, which you should have.)

Programming, or configuring, the relay uses a couple of wires and involves a series of steps in which one wire or another or both is touched to ground for 1 second, then removed. Timers.shop also has some videos one their website that illustrates the whole process well. (Timer.shop also sells a set of buttons for $5 that can be used instead of grounding wires; I'm fumble-fingered enough that I wish I had bought these but I've been able to muddle through with just bare wires – YMMV.)

The relay has 6 wires total but we're only interested in 4 of them right now; red, black, green and white. Red and black connect to a power supply – you could use a small 9V battery if you wanted – with red to the “+” terminal and black to ground. Ground and remove the green and white wires according to the following steps and you'll be good to go.

Note:
  • “W & G > ground” means to simultaneously ground both white and green wires
  • “> P/S + terminal” means to connect the wire to the power supply's positive terminal
  • "W > grn, 22X” means to ground the white wire 22 times
  • etc
White Wire​
Green Wire​
Red Wire​
Black Wire​
Step​
(or Button #1)​
(or Button #2)​
(power)​
(ground)​
Purpose​
1​
W & G > ground​
W & G > ground​
> P/S ground​
set up programming mode​
2​
>P/S +terminal​
Power on​
3​
Remove W&G fm.​
grnd after 1 sec.​
Now in program mode​
4​
W&G > grnd, 1 sec.​
W&G > grnd, 1 sec.​
prep for timer function config'n​
5​
W > grnd, 22X​
set function as #22 - “Follow”​
6​
G>grnd, 2X​
configure trigger​
7​
W&G > grnd, 1 sec.​
W&G > grnd, 1 sec.​
prep to set output config​
8​
W > grnd, 1 sec​
instant output​
9​
W&G > grnd, 1 sec.​
W&G > grnd, 1 sec.​
prep to set output type​
10​
G > grnd, 1 sec.​
reverse output​
11​
W&G > grnd, 1 sec.​
W&G > grnd, 1 sec.​
finished programming​
12​
FINISHED, disconnect everything, insulate W & G wires, install timer in circuit

(ARRGH! The table thingy here doesn't let me merge cells so I'm tryin' to make do ... work with me here, eh?)


AAANnndd – good luck!
 
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