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As you have a 12v+ supply at the solenoid (Yellow/red wire) from the starter button, you will also need a neutral switch or clutch switch to complete the circuit.Do you have a wiring diagram for the F model?...the earlier CB550 K0,K1 does not apply
As a temporary job until you get a neutral switch find rhe wires in the headlamp shell that would go to the clutch lever switch and join them together
Only 500/550 ones mate so yes. I only sell them as pairs with rotor and they cost me a lot to import so it comes out at £30 posted to you. If you want one PM me youre details
What are your voltage readings across the battery at tickover ,2000, 3000,, 5000,rpmWhat made you pick a lithium battery when these charging systems were made for lead acid batteries. Different types of batteries require different charging regimes. Lead acid, gel, AGM, lithium etc unfortunately these days 12v batteries are not just 12v batteries. I would advise anyone with these old bikes to stick to good old refillable lead acid batteries.
I’ll declare here... I’m not a sparky.But tbh, I think you’re worrying over nothing (ie 1v drop), and if the electrics are otherwise good just put the sidepanels back on & enjoy the bike.Your post intrigued me, and so I measured the voltages on my 750K2 & 400F.Both bikes have new everything, including looms, OEM VRs, rectifiers, fuse boxes, overhauled switch gear, Newtronic (breakerless) ignitions (tho’ OEM Coils)... and notably LiFe batteries.The 750 battery reads 13v (no load & across its terminals), and at the Voltage Regulator (ign on & across Black & Green wires) this is then 12.6v. Coils + Newtronic On (via the kill switch) drop the voltage at the VR to 12v.The 400 battery (identical unit) reads 13.1v (no load & across its terminals), and at the VR (ign on & across Black & Green wires) this is then 12.2v.Coils + Newtronic On (via the kill switch) drops the voltage at the VR to 10.7v. (this surprised me; but given the bike performs faultlessly I’m not gonna go looking for trouble here!)Your voltage drop, to me, is acceptable... and simply due the ignition switch + various bullet connectors along the way / through the circuit.The uprated coils indeed take more power than the OEM type, but I fail to see how changing them will ‘cure’ your concern... they drop the voltage for sure, simply meaning the VR will ‘hang in’ longer in order to reach the max charge voltage. As mentioned previously by Bryan & moorey, you should consider a voltage check under power; unsure of the CB550, but the ‘750 tops off at abouts 14.5V from 4000rpm. This surely will point to whether you’re likely to cook the battery...A note of caution here... the 750 / 400...& I guess 550 alternators, are on the limit wrt output. Everything switched on (OEM machine), and at low revs you’ll deplete the battery. I found this out from experience... hotwired an ammeter into the battery circuit, and at less than about 3000rpm noticed a drain. I now ride ‘lights off’ when about town etc. (my point is here, your new coils will exacerbate the charging issue)Finally moorey, take your point in respect of these 1970 machines. I was in a position of only getting to ride my bikes a couple of times a year (worked abroad) and was bored of returning to flat batteries. I talked to the guys at Carrot Batteries, took the punt, and bought the LiFes. Expensive... £150 or so iirc, but these things are amazing. They weigh nothing... it’s like an empty plastic box - wow. They have internal circuitry to tolerate ‘agricultural’ charging (!). But, best of all, they maintain voltage regardless of lack of use... I could go > a year with no worries, no maintenance charging is needed. The final biggy is their longevity... I think mine are abouts 6yo and still going strong - this offsets the initial purchase price somewhat. (I’ve got a 3rd LiFe in my 2011 MotoGuzzi - again, no issues; really pleased with it)There is of course a downside to these batteries is you’ll need to buy a special charger... they drain just like any other battery if you leave lights on / excessive cranking etc.Would I buy them again - probably. Certainly they were fantastic whilst I rarely used the bikes... now, I guess, they’re an expensive luxury.Anyways... good luck aaron.