Topic: CB500 four k1. Connected battery wrong way round. Help

[Kaichris]

After suffering with a duff battery for weeks, today I finally took delivery of a new one, it has four terminals. I was in such a rush to fit it that I chose the wrong two terminals and got negative and positive the wrong way round
After correcting my mistake and refitting the battery the following no longer work..
Headlight, tail light, brake light, indicators, clock lights.
What have I destroyed by making this schoolboy error? Any advice would be much appreciated. Thanks.

[SF]

Check your fuses


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[Kaichris]

Sorry I should of mentioned all the fuses are fine. Swapped them with new ones to he sure.
Starter turns over and horn works.
Tail light does work when switched to last position on ignition. Pressing the horn in that position makes the tail light flash, although the horn does not sound.

[bryanj]

You have probably melted the ground wire(s) in the loom and stuck wiring together.

[Kaichris]

OK so that could be just about anywhere in the loom right? I'd just got the bike running perfectly after months of work as well.

[pjlogue]

Before yanking all the wiring I would remove all bulbs, undo connections to coils and start checking for shorts in all positive wires to ground.  You should also check your diodes in any safety circuits and the rectifier.  This could help pinpointing the problem.

-P.

[TwoTired]

Not sure about the K1, but check the green wire harness connection at the coils common to all CB550s.
Reversing the battery leads makes all the diodes in the rectifier turn on, effectively shorting the battery POS to NEG through all the harness wiring.  There is no fuse in this circuit.  If you didn't catch your mistake in time, something in that circuit heated up and failed while dumping all that energy into it.  Could be rectifier diodes, could be wire and insulation melted.  When this happened on my bike the wires inside the harness melted the insulation the green wire and any wire it laid next to inside the wrap.  All had to be replaced.

Cheers,

[Kaichris]

OK thanks for the advice. How do I go about testing the rectifier diodes ?
it was wired up wrong for a few of minutes until I realised. The idiot lights were lit up slightly without the ignition being on, then I turned the ignition on    then the penny dropped

[TwoTired]

OK thanks for the advice. How do I go about testing the rectifier diodes ?
it was wired up wrong for a few of minutes until I realised. The idiot lights were lit up slightly without the ignition being on, then I turned the ignition on    then the penny dropped

As I said, the rectifier is always connected and unfused.  Damage occurred as soon as you connected the battery.  Incandescent lamps don't care about polarity.

There are six diodes.  Disconnect it and make 12 measurements.  Red to yellows and green to yellows.  Reverse the meter leads and repeat each measurement.  For digital meters, use the diode test function, as this provides enough voltage to turn on the silicon junction.  Write down each measurement.  Diodes will read infinity when the polarity is reversed, and conduct when the polarity is forward.  So, you should have six readings that are near infinity.  And, six readings that read low, and they should be equal to each other when conducting.

Open/blown diodes will read near infinity with any meter lead polarity.  Shorted blown diodes will conduct in both directions of polarity.

If you have wires from plug to diodes that are cooked, these will have to be repaired before testing, or disconnected from the diode block, and bypassed to test the actual diodes in the rectifier unit.

Good luck!

[Kaichris]

OK took the rectifier off the bike and tested as instructed.
Here are the results
 
Red to yellow
1414
1369
1294

Reversed
1
1
1

Green to yellow
1376
1358
1

Reversed
1
1
1

So it's safe to say the rectifier is now junk. I'm hoping that's the only issue and no splitting the loom is required.
I'll get a new one on order. And update with result.
Thanks again for all the advice. An expensive lesson learned.

[Kaichris]

 Had one last look at the rectifier and noticed one of the wires was slightly broken. Soldered it, tested again and all measuring as they should. Put back on the bike hoping for a miracle, but no, everything the same as before.
Before I start stripping the black tape off all the wiring, could the voltage regulator be the problem? If so how do I go about testing that please?
With key at ignition position 2 the horn flashes the brake light and the front brake flashes the side light. At position 1 I get horn, starter and oil and neutral idiot lights.
Is this looking highly likely as melted wires and a short.
Nothing looks melted on the exposed parts of the loom, I've had the headlight off to check the wiring in there and nothing obvious.

[TwoTired]

Unlikely a Vreg problem.

More likely melted wires/insulation.

On my meltdown it was wires between the rectifier's position up the spine toward the coil mount for the green wire.

Had to unwrap to see the main carnage.  But some exposed wires going into the harness looked toasted, which I tracked to the main melted lump.

When doing the unwrap, you'll notice breakout points.  These get lost without the wrap.  So, get some twist ties to keep loom integrity at either side of the breakout points, as you do the unwrap.  Later, your loom will look and work the same as you replace the bad wires one by one and then re-wrap.  It's tedious but not difficult. I used a sacrificial harness of a junker to maintain the wire colors.  Skinned soldered the patched in wires and shrink tubed the joins after treating the solder join with a silicone coating.  This way if any water seeps into the harness, it won't ever corrode.  It's still working fine after 20-ish years!

Cheers,

[Don R]

 Just as an FYI a couple years ago Advance auto had the wrong battery number for our bikes and sportsters. The polarity was backwards. My parts guy checked the books and they listed the incorrect number. I went to the rack and got the proper one. 

[Kaichris]

Thanks for sharing the info about where your meltdown occurred. Are you saying it was the main run of the loom from the multi plug at the rectifier end all the way to the earth point next to the coil pack at the front of the bike. Or just the run from the rectifier up behind the bracket the rectifier is attached to? I have attached a couple of pictures.

To the chap who mentioned the correct battery, thanks for that info, I think it's correct though, pic also attached.

[Kaichris]

Or the bracket small loom

[Deltarider]

Motobatt is to blame. I see at least two options to improve on clarity where the plus and the minus is... Could have happened to me.

[TwoTired]

On my 76 CB550F, it was toasted when I got it from the junkyard 20 years ago.  A complete bike junked for electrical problems.
The green wire from the rectifier was melted from the rectifier all the way to coil ground point, and had to be replaced entirely.

The over current found the weakest section to melt through the insulation and its neighbor wires, fusing 4 or 5 together up near the spine just in front of the seat.  I don't know if that position is going to replicate for every bike.  And, I don't have specific knowledge that the battery leads were reversed on my bike, since the damage occurred before I got the bike.  It just seemed like the most likely failure cause scenario, as the original rectifier still works fine to this day.

I will say that the thick green jacket you show in your pictures was not present on my bikes, as I recall.   Have you already started disassembly?  If not, I suspect prior tampering.

You can troubleshoot which wires are shorted together from end points and probing the connectors.  Disconnect the circuits at both ends.  But on mine, with careful examination, I could see some distortion in the wrap.  Subtle, but there just the same.

FYI, I never removed the harness for my repair.  I just unwrapped and replaced the bits fried with it still attached to the bike.

Cheers,