what fails next, after the fuse?

[jimhickcox]

My 1978 GS750e was running fine a few days ago, and yesterday as well. I went to start it today, and when I hit the go-button the lights all blinked off.

No problem, right? Swap the single fuse that exists and I should be good to go. I'd never done the fuse on this bike, but I found it, and the previous owner was running a 32 amp fuse. I was running it too, I guess, by virtue of never having looked. Dumb.

It didn't look blown, but there was a little blob of metal floating free, so I traded it out for a 20a (I think they ran 15a, stock, but I generally see 20a recommended), and no dice. Still acts like the fuse is blown. If I kick the kickstarter, the lights glow up for the duration of the stroke. I imagine if I kick enough to start it, it'll run, but I haven't proven that yet.

Seems to me that there's a battery connection out. It's not at either terminal, I checked them. And the battery isn't dead, I checked that and then tested it with a jump box as extra confirmation. It seems like the next step is to start digging into wiring and hope I can find an obvious issue.

Is there any wisdom floating around on common things this could be? Do I need to try bypassing the kill switch? It can't be the starter/button/relay, because then at least my dash lights would be on. I didn't see or smell any smoke when it happened, so I'm worried that whatever cut out won't be super obvious (although I do appreciate the bike not catching on fire).

I'd appreciate any help y'all can offer that might expedite my search.

[jimhickcox]

I am much dumber about electrical than mechanical (part of the reason I like old pre-computer vehicles), but I did just think to check continuity between the negative terminal and the frame, and that's good. So I have ground. That's something.

[jimhickcox]

The whole time I've had this bike it's blown headlamps. I assume it's because the old wiring has extra resistance and that's spiking the voltage. A couple of years ago I switched to an LED lamp, because they're already designed to shed extra voltage, and haven't had an acute issue since.

I worry that this current issue means it's time to re-do the whole harness. Because that likely means pulling the bike apart, not having the time to really focus on it, and then it falling into disrepair.
Sorry, this is isn't me asking for help anymore, this is just me venting. I do still need help, though.

[jimhickcox]

Spark tester indicates that I'm getting power to my plugs.

Why haven't I started it yet? Is what I would be asking me, if I were you. Because it was leaking gas from the carb overflow, and as a lazy measure before I pulled/cleaned the carbs, yesterday I did the classic run it until it's warm, then swap the fuel for chemtool until it's struggling to run, then let it sit overnight. So now the bowls are all full of not-gas. I kicked it a bunch, but not enough to get it going yet. I'll try bumping it up and down the road tomorrow. Boy I wish I had a hill.

[unfocused]

Purchase a 12v test light and a decent DVOM. The early GS750's 77-79 only had a single glass barrel fuse. You should replace with a blade type.

If you're blowing head light bulbs - CHECK your charging system as I bet it's over-charging - about 15.5 volts (? or close) will blow those old style bulbs - they overheat from over-charging
Also switch from a wet battery to an AGM - Ebay $60-ish and they're good batteries. These can handle over charging (not for long) and protect you from burning up the motorcycle.

unplug the starter solenoid signal wire (green-yellow if I remember, not the batt cables) and replace the fuse and test. most likely shorted internally. This is all the starter button does.

Orange wire from the key switch to the off/on button to the starter button then to the bike
The off/on button also powers up the coils. If the fuse blows when turning the key on and the off/on switch in ON, suspect the coils/burnt points/shorted capacitor or lighting issue.
Turn everything off, replace fuse, turn key on, did it blow, turn off/on switch to ON, did it blow.
My 77 has an off/on switch for the lights - except brake light - it always works - turn this off during testing. If nothing is found, turn it back on.

I've wired my complete ignition system - coils, pick up - seperatly from the wire harness - the original power wire for the OE ignition system is for the relay excite wire now. This relay is where I power up my ignition system now.

Your charging system does not go through the fuse (i don't remember correctly here and don't have the wiring diagram in front of me) if you go to replace with the SH775 style regulator ( you should), make sure it gets an inline 25 amp fuse for it.

I have x2 77 750's although only 1 is stock or close to it and I've been completely through my wiring and still run my OE harness with zero issues but the changes mentioned above are important.

Hope this helps

[Who Dat?]

So many things going on here, almost all of them raise some questions and some flags.

My 1978 GS750e was running fine a few days ago, and yesterday as well. I went to start it today, and when I hit the go-button the lights all blinked off.

No problem, right? Swap the single fuse that exists and I should be good to go. I'd never done the fuse on this bike, but I found it, and the previous owner was running a 32 amp fuse. I was running it too, I guess, by virtue of never having looked. Dumb.
There is no such thing as a 32 amp fuse. What you probably saw was an automotive fuse rated for 32 VOLTS (32V), the AMP rating is on the other end of the fuse.

It didn't look blown, but there was a little blob of metal floating free, so I traded it out for a 20a (I think they ran 15a, stock, but I generally see 20a recommended), and no dice. Still acts like the fuse is blown. If I kick the kickstarter, the lights glow up for the duration of the stroke. I imagine if I kick enough to start it, it'll run, but I haven't proven that yet.
While it may "act" like a fuse is blown, have you VERIFIED whether it's blown? A visual inspection is not always definitive, as it may blow under one of the end caps, where you can not see it. That 'blob' makes it questionable.

Seems to me that there's a battery connection out. It's not at either terminal, I checked them. And the battery isn't dead, I checked that and then tested it with a jump box as extra confirmation. It seems like the next step is to start digging into wiring and hope I can find an obvious issue.
Before digging very deep, make sure you have a test light and/or a voltmeter on hand. A light is quicker for finding whether you have power or not, a meter will tell you how much power, but won't be necessary for most of what you need to check.

Is there any wisdom floating around on common things this could be? Do I need to try bypassing the kill switch? It can't be the starter/button/relay, because then at least my dash lights would be on. I didn't see or smell any smoke when it happened, so I'm worried that whatever cut out won't be super obvious (although I do appreciate the bike not catching on fire).
Your previous comment about the lights blinking off when you hit the starter button raises a question about battery condition. You say it isn't dead, but please do a test. Connect your meter to the battery, note the voltage. Turn the key ON, note the voltage, press the starter button, note the voltage. If your battery really is good, it should read about 12.6 volts at first. With the key ON, it might drop to about 12. Pressing the starter should make it drop no lower than 11 volts. If it goes lower, replace the battery.

I'd appreciate any help y'all can offer that might expedite my search.

--I am much dumber about electrical than mechanical (part of the reason I like old pre-computer vehicles), but I did just think to check continuity between the negative terminal and the frame, and that's good. So I have ground. That's something.

--The whole time I've had this bike it's blown headlamps. I assume it's because the old wiring has extra resistance and that's spiking the voltage. A couple of years ago I switched to an LED lamp, because they're already designed to shed extra voltage, and haven't had an acute issue since.
Headlights 'blow' for one of three reasons. 1. Age. They simply wear out due to the way they work. 2. Mechanical agitation. Shake it hard enough, you can break the filament. 3. Over voltage. Apply too much voltage, it will melt the filament past its limits. And LEDs do not 'shed extra voltage'. They might have an internal regulator that can handle a modest over-voltage, but they do not shed anything.

I worry that this current issue means it's time to re-do the whole harness. Because that likely means pulling the bike apart, not having the time to really focus on it, and then it falling into disrepair.
Sorry, this is isn't me asking for help anymore, this is just me venting. I do still need help, though.

--Spark tester indicates that I'm getting power to my plugs.
If you have spark, you have power to the coils. If you have power to the coils, your fuse is likely good, but test it, if you haven't already.

Why haven't I started it yet? Is what I would be asking me, if I were you. Because it was leaking gas from the carb overflow, and as a lazy measure before I pulled/cleaned the carbs, yesterday I did the classic run it until it's warm, then swap the fuel for chemtool until it's struggling to run, then let it sit overnight. So now the bowls are all full of not-gas. I kicked it a bunch, but not enough to get it going yet. I'll try bumping it up and down the road tomorrow. Boy I wish I had a hill.
Gas leaking from the overflow can be caused by stuck or incorrectly-set float level, or by a broken o-ring around the float needle valve. Soaking in Chemtool overnight is not going to fix either one. Might not hurt anything, but it certainly won't help. And who ever said that method was "classic"? I have never heard of it.

Your votage might be high because of a faulty charging circuit. You can go through the process of checking what you have, or simply upgrade to an SH775 R/R and be done. Either way, you should check the stator output first. Once you have good voltage from the charging system, connect it to the stock harness and you will probably be good to go. And get an AGM battery as suggested. Note that "AGM" is a construction type, not a brand name.

[jimhickcox]

unfocused: Thank you. Helps a lot, I think. I haven't gotten in and traced the wires yet. Yesterday I did replace the fuse (I tried two new ones), and swapping in a new fuse didn't bring the lights back on, even momentarily.

Presuming that I have a (not nice, but decent) DVOM, and I know some basics about electronics, but am specifically scared of doing something wrong on a vehicle's harness, do you have any tips on chasing down a short? My inclination is just to check continuity between various wires and the frame.

For swapping in a blade-type fuse, just any inline fuse holder? The one that's on the bike now is just two little clips on wires, so I suppose anything is better than that.

I am running an AGM, mostly so I don't have to remember to top it off. Glad to hear it has additional benefits.

I saw Nessism was selling some SH775 r/rs a few months back, but I didn't realize they were such an improvement over stock. I wish I'd put one on then, maybe I wouldn't be here now. I'll see if he still is.

unplug the starter solenoid signal wire (green-yellow if I remember, not the batt cables) and replace the fuse and test. most likely shorted internally. This is all the starter button does.

Orange wire from the key switch to the off/on button to the starter button then to the bike
The off/on button also powers up the coils. If the fuse blows when turning the key on and the off/on switch in ON, suspect the coils/burnt points/shorted capacitor or lighting issue.
Turn everything off, replace fuse, turn key on, did it blow, turn off/on switch to ON, did it blow.

I'm not sure I can totally parse what all of this means without the bike in front of me. It's 3am here now, so it'll have to wait until Monday probably.

When the fuse (or whatever) did blow – the key was on, the switch was on, and as I hit the starter button it all went dead.

78 also has the light switch. I always leave it off when I'm parked, I figure it's easier on the battery when I'm starting it.

[jimhickcox]

Who Dat? I'll try to answer your questions. No promise on lowering any flags.
Sorry, I tried to quote, but it won't let me quote your quotes. You're going to have to trust I'm responding to your questions in order.

I will jump on a new R/R, it seems like that's a good general measure regardless. And I am running AGM (due to general laziness - a new flag).
I got it running for a few minutes tonight, but I was in a parking lot and not prepared to get voltage readings at the stator. It didn't want to come off idle anyway, so if it's overcharging I doubt I would have known. I'll try to start it again in the next couple of days (as soon as I can, anyway), and hopefully get it running well enough to do some investigation.

RE: 32v - That makes a lot of sense. It was dark and the fuse was dirty and just cleaned and squinted until I saw one number and then I catastrophised. And then I threw it away. Honestly, that's good news, because I realized later that I'm definitely the one who put that fuse in there the last time it blew, two or three years ago, just after my headlight caught on fire (and shortly before I switched to an LED). I failed to confirm that the fuse had definitely blown, because fuses are cheap enough that even almost-blown is trash to me. I swapped in two new ones and the lights didn't come on. I even bypassed it, briefly, touching the contacts together, and the lights didn't come on. So I feel pretty confidant that my problem is past the new-fuse stage.

Right now I'm guessing I have some kind of a short somewhere? The battery on this bike does discharge over a week or so, so I always assumed there was parasitic drain (but from what, it has no accessories). It's been low on my list for a long time, trying to chase that down (because I hate doing it and don't mind kickstarting). Maybe that's related.

I have been metering things. When I said my battery wasn't dead – it's around 10.5v (like I said, slow drain), which should be enough to at least get a little glow out of things. But I did try hooking up external power just to be sure and still nothing. It's about two years old, the battery, and it's a Yuasa AGM. There's a chance it's bad, and I can to a voltage drop test like you say once I've charged it and it's firing the starter again, but first I have to get everything going again.

As I said, when I was blowing headlights I am pretty sure it was from too much voltage. My rube's guess was that that voltage was from the same amperage going through extra resistance and spiking voltage (because I know Ohm's law, but maybe not when to use it), but probably a 45 year old R/R makes more sense.

Maybe "sheds voltage" isn't the right terminology here. I'm not an LED-driver engineer. The drivers are designed to take more voltage than the emitters need, and have their own built-in regulation system (I think they turn most of the excess into heat but I'm not sure). Point is, I know they can handle 12-14v and I figured one could deal with however much my bike is spiking over that, and so far I've been correct.

FWIW the bike only ran for about five minutes tonight (and only on choke), but it didn't leak. I'm not so audacious as to call the leak cured, but typically it starts spitting up pretty immediately. The classic-in-my-community-but-I-guess-not-yours method I mentioned seems to work about 20% of the time for me. Both my bikes (this one and a 1981 gs550) tend to leak from the overflows if they sit for more than a week or two. Almost half the time I can fix it by ignoring it and driving for about twenty minutes. If that doesn't do it, this does sometimes. And if not that, I have to pull and clean the carbs. I think it's just gunk or ethanol or something.

[jimhickcox]

I kicked it and kicked it and then bumped it and bumped it. I spent probably half an hour running around the school parking lot next to my house.
It's 75 degrees F here at 3am and that's all I could muster.
I am in: central Texas.
I am not in: shape.

Anyway, I got it running for a couple of good spurts. Something like five minutes total. Not enough to get it off choke. Long enough that I would have thought it would at least be through the chemtool and back into gas, but it sure didn't want go like it normally does. Really makes me wish I had a machine that'd spin the rear wheel in place and get it going.

It does run, though. And when it runs the lights are on. So whatever is happening, it's between the positive terminal of the battery and the rest of the system.
I'm going to try to run through the things unfocused said this week. And pick up a SH775 as per both unfocused and Who Dat?, though that'll take a little longer.
Hopefully I get it going. I'll post again as I move along, in case any of this is helpful to anyone else at some point.