79 GS550 No Spark Electric Conundrum

[BeardmanSam]

I've a 79 GS550 which is currently vexing me with a no spark issue. Previous owner drilled the key switch when he lost the key. Thereafter he had no spark and no crank. Bike will not kickstart, although the kicker does turn the motor. I know for a fact that the bike ran last summer (PO is a neighbor, he was riding it last year).

I've replaced the key switch and verified that it is working correctly. I get switched power everywhere except for the engine kill switch/starter button circuit. I have a new good battery. Voltage coming into the fuse for this circuit is about 12.6 or so when measured to ground. When I check volts to ground at the plug for the engine kill switch I get nothing. If I try to check volts to ground off of the output side of the fuse it immediately blows. Chasing wire hasn't revealed any obvious damage.

I've got a bit of electrical experience from industrial work, but I've never seen something like this happen before. I tried a bunch of googling and searched the forum here but found nothing useful. Maybe my search-fu is bad. If anyone more knowledgeable than me could offer some insight it would be much appreciated.

[pdqford]

Howdy neighbor,
I’m not more knowledgeable than you, and I’m not sure just which fuse blows, but if your meter sucks up enough current to blow the fuse, are your meter leads plugged in for measuring amps?

Hope an expert comes along soon. ��

[BeardmanSam]

Howdy neighbor,
I’m not sure just which fuse blows, but if your meter sucks up enough current to blow the fuse, are your meter leads plugged in for measuring amps?

Hope an expert comes along soon. 🤔

If it helps clarify, the fuse in question is a 10A leading up to the engine kill switch/start button. Meter isn't actually capable of measuring amps. It's a cheapo, just ohms & volts AC/DC. I can get voltage readings from both sides of all other fuses just fine. I'm leaning toward just running another line up from the fusebox to the engine kill switch. It's just wierding me out because of the fuse popping when I check for voltage coming off of it to ground coupled with the fact that I see no obvious damage to the wires.

[pdqford]

If it helps clarify, the fuse in question is a 10A leading up to the engine kill switch/start button. Meter isn't actually capable of measuring amps. It's a cheapo, just ohms & volts AC/DC. I can get voltage readings from both sides of all other fuses just fine. I'm leaning toward just running another line up from the fusebox to the engine kill switch. It's just wierding me out because of the fuse popping when I check for voltage coming off of it to ground coupled with the fact that I see no obvious damage to the wires.

yep, that helps me out. i’m Looking at a generic GS wiring diagram. That ignition fuse circuit (yellow/white wire ?) passes through two connectors on its way to the kill switch. Not sure where those connectors are located on the 550. Possible poor connection, but you have that covered with running a new line.
Weird that the DMM can only pop that fuse. I’ll be in lurk mode to see what you find.

Edit: Oh, and if that kill switch is malfunctioning, the starter button won’t get any power.

[Redman]

.....
...... When I check volts to ground at the plug for the engine kill switch I get nothing. .
..............

Which is the same circuit that poweres the Ignition.
THe circuit is :
- Igntion fuse to the kill swtich.
- From kill switch to the starter button and also over to the (org/wht circuit) igntion coils and to the ignitor.

.....
.....
...... . . . . . .. If I try to check volts to ground off of the output side of the fuse it immediately blows. ..........

The meter, in volt mode, should not pull much of any load. Sure you have meter in volt mode. If it were in amps, well, then it will draw lots of current (usally has fuse in meter that will blow).
Maybe the fuse blows just from moving something around when put the meter lead in place. Try poking around with something else and see if same happens.

[Big T]

That's good, but a 79 doesn't have an ignitor
The first connection from the fuse box is only a few inches away
Pull the fuse box and find that connector

[BeardmanSam]

Thanks all for the input so far. Unfortunately I won't have time to work on the bike until Monday sometime. I'll be sure to update when/if I find anything.

[BeardmanSam]

Update of sorts: Still no luck, but made some progress. Today I ran a new line from the fuse box to the engine kill switch. Had 12.6ish volts at the switch. Fuse still blows if I check volts to ground directly off it (so weird to me, good thing I can get glass fuses from work). Still no crank and no spark. Shorting the starter relay does crank the engine, but still no spark. Jumping 12vdc to the coil on the starter relay engages it and cranks the engine as well. Again no spark.

Checking more voltages I have no volts at the spade connectors to either the starter relay coil or the ignition coils. I've also managed to run the battery down to less than 12v. So between that and frustration I think I'm done for the day. Time to charge the battery, drink beer, and decompress. Ignition coils test good based on info from bikeclliff's website.

Tomorrow I'm going to try replacing the rest of the circuit. I have a spare set of right-hand controls that also test good. Will run new wire and connectors to the ignition coils and starter relay. If that doesn't do it maybe I'll curl into the fetal position and cry.

[pdqford]

Fuse still blows if I check volts to ground directly off it (so weird to me, good thing I can get glass fuses from work)..

Does the fuse blow if you check volts to ground with the meter turned off?
Or does the fuse blow if you just probe the fuse clip with a non-metallic probe?
Might be worth pulling the fuse block and inspecting the back side of it.

[pdqford]

Update of sorts: Still no luck, but made some progress. Today I ran a new line from the fuse box to the engine kill switch. Had 12.6ish volts at the switch.
.
.
Still no crank and no spark.

If that kill switch is fubar, it won’t pass those 12.6ish volts on to the starter button (and starter relay), or on to the coils.
Might be worth isolating the kill switch and With the ohm meter verifying that it can make and break.

Does the 550 have a clutch interlock for the electric starter?

[Killer2600]

Today I ran a new line from the fuse box to the engine kill switch. Had 12.6ish volts at the switch. Fuse still blows if I check volts to ground directly off it

You have 12.6ish volts AT the kill switch?

Please explain "check volts to ground directly off it" and how it's supposed to be different than your 12.6 volts. ELI5 and teach us how you "check volts to ground"

[BeardmanSam]

You have 12.6ish volts AT the kill switch?

Please explain "check volts to ground directly off it" and how it's supposed to be different than your 12.6 volts. ELI5 and teach us how you "check volts to ground"

By directly off the fuse I mean one probe on any ground point (be it frame, engine, or straight to the battery post) and other probe on the end of the fuse.

Does the fuse blow if you check volts to ground with the meter turned off?
Or does the fuse blow if you just probe the fuse clip with a non-metallic probe?
Might be worth pulling the fuse block and inspecting the back side of it.

And now it occurs to me that the pressure from the probe might be wiggling the fuse holder enough to short it to ground? I'm out of 10a fuses though so testing that hypothesis will have to wait a bit. Maybe a fuse box upgrade is in order.

If that kill switch is fubar, it won’t pass those 12.6ish volts on to the starter button (and starter relay), or on to the coils.
Might be worth isolating the kill switch and With the ohm meter verifying that it can make and break.

Does the 550 have a clutch interlock for the electric starter?

I do get continuity through the kill switch in run, no continuity in off. I also get continuity from line out of the killswitch to line out of the start button when depressing it. Bike does have a clutch interlock. I get continuity through it when the clutch is pulled in (currently zip tied down actually).

Thanks again for all the help. I'm really hoping I can get this bike up and running reliably before the end of the season. Even if it means forgoing the electric start entirely. My daily ride is kicker only, so that's really not a huge bother.

[Killer2600]

By directly off the fuse I mean one probe on any ground point (be it frame, engine, or straight to the battery post) and other probe on the end of the fuse.

Ok, I'm confused. Your update said you have 12.6 volts at the switch (kill switch I assume) which comes after all fuses so why do you need to check voltage at the fuse?

Further research shows that the GS550's only had a single 15A fuse that would keep battery power from getting anywhere else in the bike if bad or blown except for the starter relay.

You blow the fuse when you attempt to test it. As I see you have gathered, you might want to check that area for exposed wires/connections shorting to ground when you touch the fuse. If the fuse doesn't blow by touching it with only your hands then it seems your meter would be to blame.

[BeardmanSam]

Ok, I'm confused. Your update said you have 12.6 volts at the switch (kill switch I assume) which comes after all fuses so why do you need to check voltage at the fuse?

Further research shows that the GS550's only had a single 15A fuse that would keep battery power from getting anywhere else in the bike if bad or blown except for the starter relay.

You blow the fuse when you attempt to test it. As I see you have gathered, you might want to check that area for exposed wires/connections shorting to ground when you touch the fuse. If the fuse doesn't blow by touching it with only your hands then it seems your meter would be to blame.

Yeah, if it ain't obvious I really don't know what I'm doing . I gave up on my last project because of nightmare electrics. I was really hoping the electric issues with this bike would be minor and help me learn a bit more. Instead I find myself confused and stressed. I really love this bike, it fits me so well, I want it to run, but I find I'm seriously lacking in the ability to get it to do so. As I said in my first post my electric knowledge is limited. It mostly comes from having to troubleshoot industrial equipment, I'm way out of my league here. I'm probably missing something stupidly basic, but I lack the knowledge and terminology to make that obvious to outside assistance from the internet.

Either way, I have a new generic fuse box and inline fuse holder (for the main) coming sometime today. I'm about out of wrenching time today tho so it'll probably wait until this weekend. I've run new wire all the way from old fusebox through "new" killswitch/start button and to the coils. I still get no crank & no spark. If I have to rewire this whole bike from the ground up to make it work that'll be what I do!

[Killer2600]

I still get no crank & no spark

Well you won't get spark if the motor isn't cranking/turning.

When you try to start the bike, do you hear the starter relay click? If no, check for power on the yellow/green wire at the starter relay during a start attempt. If you do hear the relay click, ensure the motor/engine is able to turn (not locked up) and then turn attention to the starter and the power connections for it.

After you get the bike cranking, then tackle the spark. Fix one problem at a time.