Topic: CB550 Basic Wiring To Run Bike

[campbmic]

I have a 1975 CB550 that has set for about 4 years. Prior to that the wiring harness was cut up pretty severely, to the point where I'll either need to buy a new harness or build a simplified one (my bike has no signals or starter).  Anyways, I've rebuilt the carbs and air filter but Im not getting any spark from the plugs.

I have current on the blue/yellow wires that run from the points to the coils. Each coil also has a black/white wire coming off of it, running back into the cut up harness. I'm guessing this is my problem.

1. Are these ground wires or where do they need to go? For some reason I thought I remembered them having current in them.

2. Once I get these black/white wires fixed should the plugs fire? Or is there something else I would need to fix?

Thanks for any help! I know I need to get the cut up wiring harness fixed and I won't ride the bike until its done. Im just trying to work my way through each section of the wiring harness at the moment!

[TwoTired]

If a wire on the bike never caries current, it is not needed on the bike.  Ground wires carry current, too.  that's why there is a positive and negative post on the battery.  Current flows in loop out to user and back to battery.

Honda uses black color for distribution of +12v power coming from the key switch.  Green is the battery return.

The FAQ has list of wire color codes and function used on our bikes.

I don't understand why you would work on this bike without the shop manual and accurate wire diagrams.

Cheers,

[calj737]

The BLK/WHT wires run to your coils from the KILL-RUN switch. They need to provide +12v to the coils. The BLUE and YELLOW wires come from the ignition.

You can temporarily bypass the KILL switch and run a direct lead from battery + to the BLK/WHT but understand the coils remain energized and will get very hot, very quickly in this manner.

You need a solid ground wire between the motor/frame to the battery - terminal too.

[campbmic]

TT - I have a shop manual and wiring diagram for the bike. The harness is so badly cutup/rewired its hard to make it out. Im not that great with wiring to begin with, but am trying to figure it out.

Calj- The bike actually doesnt event have a kill switch. The key was used to turn everything on. The battery does have a negative terminal connected with a wire to the frame and the cut up wiring harness. If the key is only in the on position when the bike is running, will the issue still happen with the coils heating up? Or does the danger come in not running the bike and allowing the + current to flow into the coils?

If I understand this correctly it sounds like the black/white wires should be hot when the bike is running. My blue/yellow wires were both hot, should they only be hot when the points are closed?

My plan is to figure this all out then either rebuild the harness or make a new one.

[campbmic]

I just went out to check on the bike and to recap the yellow and blue wires running to the points are hot. The black/white wire running to the coils is also hot. Not sure why Im not getting any fire on the plugs. When I parked the bike 3-4 years ago it was running so Im assuming the coils are ok.

[TwoTired]

The blue and yellow wires become "hot"  (have voltage on them) via the coil windings connection to 12V.  The point make contact and complete the circuit when they are closed.  When the points close the yellow or blue wires should have ground potential (not hot).

Since you say the blue/yellow wires are always hot, I suspect you have points closure or contact issue.  They could be crusty or oxidized or maladjusted so they can't ever close and make the coils charge up.

Cheers,