Topic: 74 cb550 help

[Jkling]

1974 CB 550 four . I've had 8 of these all mid 70s over the years and not experience anything like this . Bike runs great sitting there with nothing on . Nothing I mean no headlight nothing . Any time I close any electrical switch it's immediatly kills engine . Like a kill switch would do . By any switch I mean break light either turn signal head light and horn . All electrical devices work and Come on when switch is closed but engine dies fast than I thought possible . While idling or driving . I can kick start  this thing and ride all day long but moment I hit rear break its dead ( electric start has never worked ) . Has brand new battery , no fluses blow . Whne that I everything with a meter and no shorts to be found . Where should I go from here ? This bike is really a great bike and k want to get on it very soon any help would be amazing thanks so much . I've read all threads about this type of thing but no one has had this exact issue that I've found .

[BomberMann650]

I'd hazard a guess.  The ground wiring is messed up.  Probably criss crossed circuits.
A colorized wiring diagram will help set ya straight.

[calj737]

The way the bike is wired, those switches pass current when activated. If closing a switch kills the bike, then likely you're shorting to ground.

The only wire that is mostly in common with the coils and all other switches is the solid BLACK wire coming from the key switch. It runs to the KILL/RUN then to coils; it runs to the left side controls thru the Turn Signal Relay (Black to Grey then to the LH), plus the BLACK is wired to the rear BRAKE switch. So, with that I'd put a meter on BLACK and check for continuity to GROUND at each switch when open, and when "closed". You don't need the bike running for this test to measure continuity but you might need a second set of hands to hold the probes on either side of the switches and wiring.

Hope that helps-

[TwoTired]

I'll ask about the battery charge condition and integrity.

The alternator can make enough power to run the bike at idle.  But, extra loads overwhelm the alternator output, the voltage falls and the the coils can't fire the plugs with low voltage.  One work around is to rev the bike so the alternator can make enough power to run the ignition and the lighting.

I would prefer to have a known good and fully charged battery to supply the current that the alternator can't provide at idle.

Cheers,

[Deltarider]

The phenomenon you describe is a bit odd as there are no fuses blown. Black wires are supposed to be fused. Makes me wonder how original the wiring is and if a PO has changed something, like installing an improvised antitheft device, fitted a relay* or changed/used anything at/of the socalled starting motor safety unit. Is the ignition set up still original or do you run an EI?
* It's almost as if someone has fitted a relay wrongly or used the wrong type of relay.

[strynboen]

korosion somvhere in the batteri konnektion can delevere just the ignision power..as you turn somthing ekstra in..the restistins in the korosion vorks like restister and it takes all power up..so you can only pull abaut a 1 amp..if more are used the voltage is dropping total Down and kill the coils..tru to messure the voltage at the coils..and see for a drop..vhel you turn a. ekstra power user on..

[Jkling]

Ok so there wish only one 15 amp fuse . All lights / work and flash and battery is chat being perfectly . I agree somthing is dead shorting to ground . But all loads work and stay working once engine dies . Wiring has been messed with but all looks ok . There are no gauges and thus no lights to them they have been isolated well and I've Checked that first . That's all that looks like has been Done . Not having those 4 bulbs won't cause this . I'll keep digging . I've already unplugged all loads / lights and still closing any switch kills engine and fast / instant kill switch .

[Jimray23]

If you have disconnected all the loads from the switches, and it still happens, then it is a short. Probably close to the end of the black wire circuit. If its shorted at the end of the black wire circuit, everything before the short will still work. Nothing after the short will work.

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Jim
I really don't see why people ask for advice if their not going to take the advice given.