First Post, Big Problems - electrical failures up and down

[AustinJon]

Long-time lurker, first-time poster.

first, my bike is a 1981 cb750c.  I've done that thing that causes people to shake heads judgingly and I've converted it into a cafe bike. Sort of. slowly.  Still in progress. I bought it in great shape in Michigan and it's now down with me in Austin, TX.  

Starter relay died on me one day, so I looked around for replacements.  OEM I found was like $90 and had that weird fuse on it, so I went for a probably-way-too-cheap aftermarket one on Ebay.  Ran fine for a month, then one day I went to turn it on and it smell like burning, I pulled off the side cover and the starter relay had spontaneously combusted.  Battery and starter connections had largely fused to the relay and the relay itsel was a black pit.  The molex connector that plugs into it had become part of the relay.

So, I went to a honda dealer here and talked to the parts guy who owns a '78 750.  He admitted that he doesn't use the OEM starter relay and bought an aftermarket one for the fuse, so I bought that brand. It seemed, at first glance and touch, to be much higher quality than the POS I'd bought on Ebay.

I thought I could clean up the connections, replace the wires and this would be a 1 hour fix.  I think I've put 20 hours into it at this point.

The following things died/failed, all at the same time:
1) The Starter Relay
2) The clutch switch (determined because I can succesfully bypass it, alligator clipping green/red to green where they would enter the clutch switch)
3) Clutch/neutral silicon rectifier (determined because I can clip from the light green/red circuit straight to the starter relay and the bike will crank)
4) I ran out of time to narrow down the last issue, but even though I got it to crank, I get no spark. From either ignition coil.  I guess it's possible they are both fried.  I have the manual instructions on how to test the ignition coils, but I ran out of daylight.

This is the first bike I've ever owned and the first thing I've ever done much work on mechanically.  I have a decent book on motorcycle repair and I do have the service manual for the bike.

I'm wondering:  Before I fix all this, should I be worried about something else?  I don't know much about the more advanced electrical components like the regulator/rectifier, but it seems like something fried this all at once.  Barring a lightning strike, what should I be investigating?  That's an awful lot of damage (and a pain in the ass to troubleshoot when 3-4 things failed simultaneously).

Thanks in advance for any help.  I think I'll be spending Christmas Eve in the driveway...

[TOOLS1]

You obviously have a dead short. It might have been the starter solenoid/relay. However I have to ask, because the original solenoids hardly ever go bad, was it the solenoid, or the fused link that went bad? Also on the neutral switch, it has juice coming to it from the light when the ignition switch is on. What the switch does, is make a ground connection when the bike is in neutral.
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[AustinJon]

The way I understood that Diode/rectifier was that it prevents the clutch switch circuit from lighting up the neutral light, but allowed the neutral circuit to power the clutch circuit to the starter relay.  Basically allowing either neutral or clutch to permit the starter switch to do it's thing.  Me directly connecting that neutral (light green/red) circuit to the dark green/red clutch circuit was what allowed the bike to crank.

On the original issue, the actual relay went bad.  Tapping on it with a wrench when starting would do the trick for a while.

Are you of the opinion that the cause was likely the cheap relay itself?  I just don't want to fix all this and have it happen again.

 I feel like electrical is a steep learning curve, but I think I understand my electrical diagram pretty well now and I've used a multimeter more this weekend than I have the entire rest of my life.

[TOOLS1]

I did not realize you were talking about the neutral safety switch. I am not very familiar with how that works. However I would suspect the cheap solenoid of shorting.
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