Motorcycle Repair: 1975 Honda CB125S Electrical Problem, honda cb125s, ac volts

Question
Hi Bill,

I have a 1975 CB125S electrical problem.  The tail light blinks (lightly) with the turn signals.  Seems the headlight is dim and drawing down system as well.  Appears to be charging ok.  Bright and neutral indicator lights also blink somewhat with the turnsignal on.  Affects the running as it cuts out with the headlight on especially the bright.  Any help is appreciated.  This is the last problem I need to remedy.  I've had this bike 20 yrs and sat mostly in the garage.  Want to get her in good shape and start riding.  Thanks.

Answer
Doug, you have to start with a healthy fully-charged battery reading around 6.75v.
The "charging system" is basically a maintenance system. With the "always on" headlights, everything has to be in top shape as far as components, battery and wiring.
I have had one or two of these bikes and a little blinking is to be expected, when the signals are flashing. Check all ground connections for all of the lights.

They rewired the electrical system to allow the headlight to be ON all the time, in 1975, so check all of the wires inside the headlight shell for clean and tight connections and proper wiring color combos. Your owner's manual will have a wiring diagram or get a shop manual with the specific year's diagram. Try Ebay or www.motorcyclememories.com or www.helminc.com

Because the ignition system is battery operated, once the voltage drops down in the 4-5v range, the coil doesn't get enough energy to keep the engine firing at high speeds.

Be sure that neither of the brake light switches are stuck
ON, as that will drop the voltage very quickly. Check rear brake light adjustment and rear brake pedal return action.
Front light switch is a plunger type running off the brake lever, mounted in the bracket.

Do a temp hookup on the battery with a volt meter and drive the bike to see what is happening. There is a small rectifer to convert stator AC volts to DC. All connectors have to be clean and tight. Sitting for 20 years can cause oxidation of the contacts.

I wouldn't run the HIGH BEAMS on all the time when you are riding, especially in stop and go traffic conditions. The charging system doesn't really get going until about 3k rpm or more.

Bill Silver