Short to ground troubleshooting - help please?

[halliday77]

Hi guys,

I've been reading the forums intently trying to work out what might be wrong with my bike, but my patience is wearing thin and despite picking up some new skills, I'm getting a bit over it.

Here's the skinny:

- '81 Special, almost all original, brilliant condition.
- Bought it in Victoria two weeks ago, started and ran well.
- Put it on a transport truck to NSW. When they unloaded it, it started and ran well.
- Five minutes after that, I gave the throttle a decent squeeze and the bike cut out.
- After that, turning the key to 'on' only produced lights intermittently for about 5 minutes, then not at all.
- Figured it was the battery, bought a new one. No change.
- Closer inspection revealed a blown main fuse.
- Replacement fuses would blow instantly when hooked up to the battery.
- Read forums for two days straight, bought a multimeter.
- Spent another day working out how to use it.
- Do some tests as per the manual and isolate the problem (I think) down to regulator.
- Yank it out, test it as per manual and the resistance readings fail the manual test. Order new one. (Should be here in a few days).

Here's where I lost the plot.

- Hook the bike back up without the regulator in. As far as I understand, I should be able to get the bike to start, it just won't charge the battery while it's running. I can't do this (though I wonder if the new battery needs a charge).
- Further investigation shows that when I'm all hooked up with no regulator, I'm instantly blowing a signal fuse. No power to the headlights and console lights and (possibly unrelated) the middle console bulb is blown. Not sure if that was like that before.

So by my reading and reckoning, it sounds like I have a short to ground. My problem is I'm at a loss to work out where, and I'm not entirely sure where to start and how to test the wiring and isolate the problem part/wire.

I have all the right tools, plenty of time and determination, and there's still a BIT of patience left.

If any of you could help me out by putting me on the right track as to where I should start, and how exactly I go about testing the circuits, I'd really appreciate it. I love figuring this stuff out and it's so much more satisfying if I can nail it on my own. Just need a bit of guidance.

Thanks in advance guys!
Hope to hear from you.

 

[pamcopete]

halliday,

Could be about anything. I would just unplug everything from one end of the bike to the other. If that stops the fuse blowing, then you know it was one of the things that you unplugged. If so, start plugging things back in, one at a time until the fuse blows again. Also, disconnect the brushes to the rotor.

 

[gggGary]

A favorite short place (not the ONLY place) but popular is the grommets in the back of the headlight shell where the wire bundles pass through. The grommets crack and the steel headlight shell saws into the bundle. I would start there.

 

[1974jh5]

I'm with gggGary. Remove the headlight and check the wiring bundle in there carefully. If it's blowing the signal fuse, check the wires in there going to the left side bar switch, since that's where the switch is.

Quick tip: if it blows the signal fuse when the switch is in the middle (off) position, check the supply wiring coming from the harness first. If it doesn't blow it till the switch is moved to one side or the other, concentrate on the output wires.

There are also other things which run on that fuse (the horn and the brake lights) so check them as well.

EDIT: One other way to check for a short: get a 10 amp circuit breaker to replace the 10 amp fuse. Get the type like this:

These will, instead of popping, start clicking when something shorts out. So you put in the breaker, it starts clicking, you unplug items one at a time on that circuit. When the clicking stops, you have found your shorted part or wire.

Also, welcome aboard! Always glad to see an Aussie.

 

[jd750ace]

I was going to suggest the back of the headlight, and the pinch area below the seat as well. You just changed the battery. Check the harness around the battery box as well.
Good luck.

 

[tonyc]

Old fuse box.

 

[halliday77]

Thanks for the replies so far!

Great help. Cheers.
I especially like the circuit breaker idea - definitely going to give that one a go.
I bought two separate bike shops out of all their old 20 amp fuses to test with over the weekend. I have over a dozen blown ones now! Breaker seems like a much better idea.

As for the headlight bowl - all grommets and insulation intact.
The alternator brushes - also not a problem.
The whole thing really is in impressive nick for its age, and I'm sure this problem is minor. It was, after all, running fine just last week.

Something I have noticed that I'm wondering about - where the lead from my battery comes out, and goes into the (not sure what that is, actually. Right side, mounted to the frame with rubber grommets, holds 3 large enclosed fuses), that mount is missing a screw and subsequently moves around a bit. It occurred to me that because of the rubber bungs about the mounts, it is probably not meant to come into contact with the frame.

Because of the missing bolt, there's every chance that the vibration of the bike caused precisely this to happen.

What exactly are those enclosed fuses (if they are, indeed, fuses), and could this be my problem, or at least the primary cause of the subsequent blown fuses?

 

[halliday77]

Also, when I'm testing things with my multimeter, should I just be testing for continuity, or resistance?

Could someone please explain how I use the multimeter to isolate the short?

 

[halliday77]

Thanks for the advice mate.

Couldn't find a breaker fuse, so I bought a fistful of 10s instead, and took to removing components until it stops blowing. I should mention, the signal fuse blows when i switch the key to the 'on' position.

So, taking your advice, I narrowed it down to the ignition barrel. Does that mean my barrel is arsed? Or does it mean nothing because my barrel is what allows the power to flow?

Fellow Aussie?
Where are ya?

-Cheers.

 

[jd750ace]

Check the wires below the barrel first. The barrel would have to be coming apart internally to short, but it's not impossible.

 

[1974jh5]

Thanks for the advice mate.

Couldn't find a breaker fuse, so I bought a fistful of 10s instead, and took to removing components until it stops blowing. I should mention, the signal fuse blows when i switch the key to the 'on' position.

So, taking your advice, I narrowed it down to the ignition barrel. Does that mean my barrel is arsed? Or does it mean nothing because my barrel is what allows the power to flow?

Fellow Aussie?
Where are ya?

-Cheers.

I wish I was an Aussie. I'm up here in the Great Satan.

Okay, the ignition barrel would be the ignition switch. The way it works: power goes from the battery up to the switch, then when the switch is turned to the on position it supplies power to the rest of the bike through the fuse block through a wire which goes back to the fuse block. So the fuse blowing when you turn on the ignition switch does not mean the switch is the problem, unfortunately.

What is happening: something after the fuse block is shorted to ground. So here's where a wiring diagram and a voltmeter come in handy. To test without blowing a fuse: remove the fuse, then unplug the horn first. That's because the horn is on the same fuse. Set the voltmeter to 'continuity', then check for continuity from the horn power wire (it's brown IIRC, that's why you need the wiring diagram) to the frame of the bike. With the fuse out, there should be no continuity. If there is, now disconnect the rear brake light switch (on the same fuse) and check for continuity between its power wire and if there is continuity that you next go to the front brake light switch, do the same thing.

What you are looking for is whatever you unplug that makes that continuity go away. When that happens, your short is in that part. If you unplug everything on that circuit and it still has a short to ground, then there is a pinched or rubbed bare wire somewhere.

I don't know if this is where your problem is, but you also might want to look where the wiring harness goes under the back of the tank. If it's not routed properly it could get pinched and cause a short.

 

[pamcopete]

Well, there will be continuity on circuits like the brake light because the other connection to the bulb is grounded and the resistance of the bulb when cold is close to zero so when you measure from the brake switch to the tail light you will get continuity to ground. That's why you have to disconnect everything and then reconnect one at a time until the fuse blows again. You also have to remove all of the light bulbs because most of them will show continuity to ground.

 

[1974jh5]

Thanks for bringing that up, Pete. I forgot to mention it. Now, when everything is unplugged and you are checking the power side, it shouldn't show any continuity to the frame when checked as I describe.

 

[halliday77]

You guys are totally awesome!

Thank you all so much.
I've devoted the whole weekend to it, so I'll see how we go!

Last night I managed to find the time to do some more testing.
Yanked out all the connections to the rear lights and indicators - still blowing the fuse.
Started disconnecting things from the front - indicators and various bar components - still blowing.

I'll test as you guys have described and keep you posted on the developments. I'm very determined to get this licked on my own.

Again guys, thanks for the help!

Have a great weekend!

 

[pamcopete]

halliday77,

Well, don't forget that it could be the ignition switch itself came apart internally. Does it feel crunchy when you turn it? I would disconnect the switch itself and measure from each of the terminals to the switch case. Should be infinite resistance.

 

[1974jh5]

Pete, wouldn't that cause something different? According to my wiring diagram, the red wire from the battery goes through the 20 amp main fuse, then to the switch, then to the brown wire which then splits into brown/red and yellow/ red and white to supply power to the other three 10 amp fuses in the fuse block. To me, that means if the switch were bad it would pop the main fuse. Since it's only blowing the signal fuse, that says to me the problem has to be after the fuse block. Again according to my wiring diagram, the signal fuse supplies power to the brown wire only, which powers the turn signals/horn/brake lights.

 

[halliday77]

GOT IT!
Well... mostly.
I've got the laptop out and I'm referring to it as I go.

SO - I've just discovered there is continuity between the brown power wire feeding the rear lights and the frame.

When I popped back out to start tracking down the short - i can't recreate that continuity.

At this point I've got the horn disconnected, the front signals and headlight too.

I just went to test the rear brake switch - and discovered continuity between the brown power lead and the frame.

Any ideas?

 

[halliday77]

UPDATE:

Narrowed it down to some little black thing, started a new thread.
http://www.xs650.com/forum/showthread.php?t=18184

What the hell is it?

Also, thanks for all the help.
If any of you are in, or ever will be in, Sydney Australia - beers on me.

Cheers!

 

[1974jh5]

I bounced back here from the new thread. Glad you located the problem in the canceller! According to my wiring diagram, the canceller has no connection to anything else on the bike so I doubt it's the source of your other problem.

Since it's no longer blowing fuses for the signal circuit but you say you have no ignition or headlights, there are two other fuses in the fuse block for those circuits. Here's the deal: all 3 of those fuses are fed by the brown wire from the ignition switch. That wire has red/yellow stripe (headlights) and red/white stripe (ignition) wires spliced to it.

So first thing to check is to make sure that you have power on the 'input' side of the fuse block for all 3 fuses with the ignition switch in the 'on' position. That's probably going to be okay; if you have power on the 'signal' fuse, then the other two should be powered as well since all 3 share the same source. Best to verify, though. If you have power on both of those fuses on both the input and output sides but still have no lights/ignition, then something is disconnected somewhere.

According to my wiring diagram, those two wires both go to the safety relay. I have zero practical experience with those, since when I got my bike one of the first things I did was to strip the wiring to its basics and get rid of all that type of stuff. So past suggesting that you make sure it's plugged in, I don't have any more info on testing it.

I will mention that some of the latest bikes had a sidestand switch which cut the ignition if the bike was in gear and the sidestand down. That's so you couldn't ride away with the stand down. If yours has this, they are known to get goopy and cause the ignition module to quit making sparks. They are easily bypassed, if your bike has one.

 

[halliday77]

FINAL UPDATE:

After another weekend of forum-reading, fuse-blowing, diagram deciphering and profuse swearing... SHE GOES!

The signal-canceler was arsed and blowing the fuses. After I removed it, I realised I made some mistakes in hooking up the wiring in the headlight bucket, which is why I had no headlight and ignition after fixing the short.

So after some rejigging, we're back in action! Took it for a ride this morning and couldn't be happier.

It would seem even my neighbours were rooting for me. After seeing the bike in a million pieces all weekend (no garage, dead-end street, so I work on it in the road), when I finally got it fired up around 8pm last night, the bloke over the road popped his head out the window and gave me a shout and a thumbs-up!

It still needs a bit of work. Idle is too low and leads to some stall-outs, but some minor adjustment should get that.

More concerning is it slipping out of gear - mostly second - seemingly at random.
Did some reading today and the symptoms sound similar to a weak shift-drum stopper spring. I'll check that out when I get the chance. One poster said he managed to replace his without removing the clutch basket. Here's hoping I can do the same! If that is, indeed, the problem.

Just want to send a massive thanks to everyone who posted in this thread. Your advice, patience and encouragement are greatly appreciated!

To the bloke I upset by starting a new thread - my most humble apologies. Let's chalk that up to a rookie mistake.

Thanks guys!
I reiterate my offer of delicious Australian beers, collectible in Sydney if you're ever around!

Take it easy, ride safe.