The lighting coil on the CT1C has double yellow and double black female terminals (see images on link below). However, I only have one wire of each colour in that vicinity that could plug into them. Therefore, is one of each "spare", or am I missing something?

Thanks.

  COIL, LIGHTING for CT1C 1971 USA - order at CMSNL

That photo is of a new part that might have been revised over the decades?

That said, as far as I know, only one yellow (headlight) and one black (ignition) is used originally.

The extra black could be used for an additional kill switch.

The extra yellow could be used for a regulator...  I'd only do that if bike is ridden with lights on...  regulator gets pretty darn hot connected there if lights aren't on.  (Though I know many people have done it)

Thanks Mark.

It is the same format of wires as fitted to my own bike (but see below).

Looking at Partzilla as well as CMSNL, only the ATMX and CT1 models use this part (but the ATMX doesn't have lights? ), although the 248...... part number is also shown as being used. Link to images of this below, but the wiring is identical.

2488131310: Coil, Lighting Yamaha - buy the 248-81313-10-00 at CMSNL

Another issue is that my own CT1C, as well as a new 251.... coil I have just bought, has a green/red wire instead of the white/red, and my harness has a green/red exiting with the other wires to connect to those from the mag - see photos below.

What kicked this enquiry off is that my battery isn't charging and my headlight is as bright as ........................... (insert politician of your choice here!).

Thanks again.

I wonder if you just test the AC output of each coloured wire with them all disconnected from loom then connect as desired to get the charge you want when you want it, like with lights on or not. Yellow will be lights & highest output regardless. If I'm thinking right.

The ATMX models came with lighting coils, they just weren't connected to anything.

Green is daytime charge and Green/red is nighttime charging.  Earlier models had an optional "white" wire you'd connect in place of the green for additional charging...  which, by the way, doesn't start until like 3,000 RPM.  Rectifier and/or headlight switch and/or an internally corroded harness could be cause for low voltages.  Or maybe someone beat on the flywheel and the magnets have gone weak or something?  Bad grounds? 
 
As RT325 suggested, might be time to check the voltages.  If they are weak right at the stator (disconnected from harness), then sounds like something in the magneto.  Otherwise start testing for voltages... down the line and see how much it drops as you progress down the path
 

"The lighting coil on the CT1C has double yellow and double black female terminals (see images on link below). However, I only have one wire of each colour in that vicinity that could plug into them. Therefore, is one of each "spare", or am I missing something?"

Alan, all three of my CT1s have the double female connectors and only one male connector from the harness is connected to them, so I'm confident that is standard.
As the others have said, time to check voltages.
Looks like you have an aftermarket rectifier, is that one you have added?

Thanks gents.

Yes Pete, aftermarket rectifier from Rex's, but managed to fit it to original bracket. I'll do a resistance check on it, just in case.

I'm still struggling to understand why there are unused terminals there. 

One possibility for the double connectors is that the ignitions are not made by Yamaha.  I once came across a "bitsa" 175 with a different ignition...  at first I thought it was from a later model (advance mechanism in flywheel) but flywheel number did not match the service manual exactly.   I searched ebay for the number on the flywheel and it turned out to be a Kawasaki ignition!  It really did look identical to the Yamaha version on the later models.

So it might be possible Hitachi added the double connectors to make one of their systems suitable for use on other brands or even other Yamaha models?  

"One possibility for the double connectors is that the ignitions are not made by Yamaha.  I once came across a "bitsa" 175 with a different ignition...  at first I thought it was from a later model (advance mechanism in flywheel) but flywheel number did not match the service manual exactly.   I searched ebay for the number on the flywheel and it turned out to be a Kawasaki ignition!  It really did look identical to the Yamaha version on the later models.

So it might be possible Hitachi added the double connectors to make one of their systems suitable for use on other brands or even other Yamaha models?"  

I almost made the very same comment, Mark.  However, it then occurred to me that other bike manufacturers would stipulate wire colours in line with their own requirements.

I have posted on here previously about Kawasaki and Yamaha switchgear parts being near identical (made by Asahi Denso) and I've come across two stroke oil level sensors and other electrical components that are the same. In all cases, however, the wire colours were different.

Maybe the operative at Hitachi didn't get the memo about Yamaha only wanting single connectors! 

Note that it appears the CMSL picture you posted has a white/red instead of the green/red Yamaha used?