Motorcycle Repair: electrical problems!, honda cb500, wiringdiagrams

Question
hi. i've got a 75 honda 550F that is having some electrical trouble.
previously the bike was running ok. the main fuse was getting rather hot, to the point were it was obviously distorting the shape of the fuse box, but never blowing the fuse oddly enough. recently i replaced a faulty ignition coil for the 2-3 cylinders. now that i've got the bike going again (starts right up) that fuse is blowing within five minutes, which i guess is good because thats what it there for.
the headlight and horn work fine. the neutral light works well, although the oil light sometimes flickers. the starter is not working at all and the turn signals work but seem to be somewhat delayed.
any thoughts on what may be happening.

thank you

Answer
Rick, Sounds like you could write a book on the possibilities. See wiring diagram on site below and then break out a 12v test light and strip the headlight out and the bodywork off, so you can get to all the wiring.

http://oldmanhonda.com/MC/WiringDiagrams/MCwiring.php#class


This link should give you access to a copy of the shop manual for more info:

http://drop.io/cb550manual/asset/14355713-honda-cb500-cb550-workshop-manual-pdf

In 1975, the always ON lighting rules began and Honda had to rewire the starter button to do two functions... engage starter and disconnect the headlight momentarily while starter circuit is engaged.

You mention no starter, so I would suggest you start with the starter button control. Probably the contact housing has disintegrated and the contacts are shorting out against each other. The switch assemblies are about $100 each. The starter problem could also be the solenoid, which you can jumper with a screwdriver across the two big posts to see if the starter motor turns or not. If so, then you will have to verify that the solenoid is getting power from the starter button. If it is, then the solenoid is probably gone. There is also a safety switch on the clutch lever that needs to be working.

When you turn the ignition switch ON, you get power to the ignition system, horn circuit, rear tail light and brake light, plus your instrument lighting/head light. Check all of that wiring, especially at connectors throughout the wiring harness. Make sure all grounds are clean and tight. Remove the fuse block and check the back side for corrosion or soldering issues. There was a recall on some of the fuse blocks for small Honda fours, way back when.

You do have to check your charging system output, as too high a voltage will blow the fuse and/or overcharge the battery, causing it to boil out the battery acid. There are now solid-state regulator/rectifiers for sale to replace the mechanical voltage regulator that was originally supplied.

Oil light shouldn't flicker unless you have a very low oil level or there is an intermittent ground on the pressure switch wiring line. Pressure switch is under the left engine side cover on the oil pump.

Check www.cmsnl.com for parts illustrations or similar on-line Honda dealer microfiche.

Make sure you don't have a high-watt headlight bulb and/or tail/brake light wiring/bulb issues. The bike is 35 years old now and needs a thorough look-over to ensure continued good service.

Bill Silver