Topic: CB 500 Four (1972?) Full Restoration

[MickB]

Worked all day to fix the fuse issue.

With the key off and with the meter set to continuity the black wire buzzes at the regulator end and at the switch connection under the tank. I pulled out both black wires from the handlebars so they weren't connected and still the fuse blew!

I'm stumped.

[calj737]

Mick - Shoot a couple of very clear pictures from under your left side electrics panel. I know you had to re-plug some your charging harness and you've scrounged together those parts. Its possible you've got a wire crossed, or maybe even at the solenoid? Should be 2 wires on top, a small gauge Yellow/Red and a Black. The Y/R is the earth, maybe you've got the Black tied to the frame???

[MickB]

Cal

Photos as suggested











Note the White mark next to the pin.



Also note the flasher can it turns in its housing. Is that normal? A black wire was attached to the pin where the wire mark is.



Could a dodgy regulator or rectifier cause the fuse to melt?

[MickB]

What gets me is I was riding it home when the fuse blew, I had the right indicator on when the bike stopped.
Up until then it was running fine, electrically that is.

[calj737]

From our chat the other night, and your test of continuity to ground for Black, that's pretty convincing the issue is not the Reg/Rec, but a wiring issue where black is finding ground.

That flash mark on the flasher relay and the fuse blowing with the indicators burning today is still more evidence of black shorting to ground.

You're going to have to begin unwrapping that harness tape and find where you have bare wire on the black circuit touching bare metal or the factory green.

[MickB]

I think this is the problem

Initially the female side was pushed backwards and as a result the red power was  arcing to the female and creating heat.



Then the male side was pushed out and the problem reoccurred.



The connectors are so old and worn I'll have to put a new connector to replace the old one.

I did get it to start and run after I made sure the red power was secure.

[MickB]

Reconnected the power wire, ensured male and female sides were inserted correctly - Fuse blew immediately, pulled the black wires from the kill switch- blew fuse immediately, at least I've eliminated the RH control. I don't think it was the flasher as it worked fine, as also the headlight and brake lights when I got it to run.

It must be in the electrics I think.

I didn't have neutral or oil pressure idiot lights working when I had it running and the electrics were  hanging on the side.

As soon as I move the electric plate it seems then the fuse blows, something's touching somewhere.

[MickB]

Pulled the front brake switch wire out still the fuse blew, pulled off the solenoid and it still blew!

I use the meter on continuity and on the black wire and touching the frame I get a buzzing.

I pulled both black RH Control wires then no continuity buzz and the fuse still blew??

When the RH wires are disconnected I don't get continuity buzz??  Go figure?

[MickB]

I touch the black and white wire going to the negative on the 2&3 coil and get a buzz with the key off. Is this significant? But no buzz on the 1&3 coil?

[MickB]

I just pulled off the alternator, oil and neutral harness from the electrics and it started but no neutral or oil pressure light. Everything else worked indicators etc.

The problem must be in either the alternator, oil pressure, neutral or the harness somewhere.

Could it be also in the idiot light area? It has a black wire?

I'm wondering if the alternator has a fault in it after the oil plug leaked oil into that area? Has it killed the stator or coil field?

[bryanj]

Similar alternator coils to 750 and that runs in oil so extremely doubtful for that to be problem, what is common is for the rubber round the idiot light to allow a short when it get old and fragile.

If oil switch or neutral wire shorted to ground that is what they do to make bulb light so not a probable cause, what would cause a short is if the white power feed to the centre coil was shorting somewhere, the green goes to ground anyway

[MickB]

Thanks BJ really appreciate the tips, I've had enough today, I had a look at the idiot lights and no obvious fault but I'll certainly have a closer look tomorrow.

I don't think it's the coil as it started and ran no problems with the alternator harness unplugged (no oil or neutral idiot lights however).

BJ BTW I put a new O ring on the plug today, book says 13 x 2.5, I put a 13 x 3.0 so I hope I've fixed it.

I did run the bike without the cover on and you were right it popped the oil plug out like a bullet (I only had it just sitting in the channel, I could still see the O ring) and I didn't realise, my tool box was under the plug area so I conveniently collected some of the oil in the tool box- GREAT, the rest went over the concrete!

[MickB]

BJ I just remembered I'd unplugged the black wire from the idiot lights from the main loom and it still blew the fuse.
I'm really wondering about the alternator?

[calj737]

I touch the black and white wire going to the negative on the 2&3 coil and get a buzz with the key off. Is this significant? But no buzz on the 1&3 coil?

Mick - the BLK/WHT wire is switched power, not ground! This wire comes from your RH KILL/RUN switch. The "ground" for your coils comes from the points (BL and YLLW wires).

Your idiot lights are missing their BLACK wire connection which is why you don't have illumination.

Forget the Alternator; its not your problem. Its the BLACK wire within your harness somewhere. And here's why-

Your problem only occurs when you rotate the key (fuses blow) so that is a sure sign its along the switched power side of things. If the BLACK wire rings out to ground anywhere along its branches, then you bike is sending 12v to earth, and that will cause a fuse to blow. Its as simple as that. You don't even need to run the motor to make the fuse blow when BLACK is shorted (this eliminates the REG, REC and Alternator).

Remove the tank. Pull the 2 fuses for TAIL and HEADLIGHT from the fuse block. This leaves you with MAIN. Flip the key. Fuse blow? If not, with your meter, check for 12v on the BLK/WHT wire at the coils. If 1 coil has it, but the other is shorting to ground, you will blow a fuse. This also explains why with the RH control disconnected you don't get a ground bell from the meter. You can verify this with the RH connected and the KILL/RUN switched to KILL (should be no ground tone) in RUN you should get your tone (only because you're wiring is wrong somewhere).

I'm not saying this is the problem but if you indeed have BLK/WHT grounded at the cols, that is a big problem.

[MickB]

Cal I don't have a fuse for the head or tail lights. I only have 1 fuse.
I hear what you're saying I'll look again.

[bryanj]

Just be careful you don't let the smoke escape from the loom, Lucas used to have a part number for it but long obsolete.

Start with everything disconnected and a meter from the black to ground and keep attaching things until it grounds and hopefully the last thing attached is your fault.

Normal places to look are in the headlamp where everything is crammed in and also the switch wires through the bars as sometimes the insulation gets snagged as its fed through

[RAFster122s]

You need to install the slow blow fuse...  Like this:

[MickB]

That's what I was thinking RAF

[SOHC4 Cafe Racer Fan]

You need to install the slow blow fuse...  Like this:

 

[bryanj]

Don't forget to source a bottle of Harness Smoke before you fit that slow blow fuse

[SOHC4 Cafe Racer Fan]

[RAFster122s]

I figured the smiley was a given with that recommendation, but you want the fire bottle handy if you did that...
I should post a pic of an old Volvo 245 fusebox, the ceramic fuses are perfect size to fit a 22LR in their place.
Lots of urban legend folklore of 22s being used as fuses in some hayseed's truck.

[calj737]

Okay, Mick, I got your PM about the switch. Did you get it fixed yet? Or do you need another switch housing again? With or without the ball bearing and spring 

[MickB]

Cal, big thanks for your advice today.

I found the wire that was causing the short, it was the Black & White wire coming down from the kill switch to the plug in the headlight then goes to the coils.

I pulled the switch apart - tiny springs and ball bearing, tested the Black kill switch wire no buzz!

Tested the Black & White wire at the kill switch - BUZZ! Unplugged the Black & White wire in the headlight- NO BUZZ at the kill switch.

Put the switch back together.

Tested the Black & White wire (unplugged) going away from the headlight to the coils - BUZZ! The culprit finally.

PS had a mate's son come over and helped put the headlight switch together, I needed 4 fingers in there, hold the switch, put the base into the slots and put the ball bearing on top of the spring and slide it into position - done.

Bonus was he found the lost ball bearing stuck in the grooved part where the throttle goes.

[calj737]

So now you're all good? No more quid pouring out the door after blown fuses? Think of how many new bikes you buy now that you're saving money on electrical components 

Once you do get it running and not shorting out, lets get a god test of the charging system to insure that you have no other issue lingering. Meter on VDC, test battery with key OFF. Test battery with motor at IDLE. Test battery at 3,000 RPMS, and then again at 5,000. We want to make sure you're putting out a good charge and the stator is actually working properly under there.