Tach testing

[mack]

Got the LH out for a ride today and the tach quick on me right after I made a quick button hook on the road. The harness has a fair bit of slack in ti, but I'm going to go into the bucket tomorrow and look at the connector. Does anyone know the numbers for testing the unit itself to see if it is fried.
I'll also go into the connector behind the battery box to ensure the alternator is charging but I want to see if the tach is ok before I have to go deeper.?

[motoman]

Got the LH out for a ride today and the tach quick on me right after I made a quick button hook on the road. The harness has a fair bit of slack in ti, but I'm going to go into the bucket tomorrow and look at the connector. Does anyone know the numbers for testing the unit itself to see if it is fried.
I'll also go into the connector behind the battery box to ensure the alternator is charging but I want to see if the tach is ok before I have to go deeper.?

Electrical connections behind fuse panel and connections under alt. cover have been known to get 'crusty' lookin' and are nototious for causing erratic tach or none at all. Suspect that BEFORE suspecting tach itself.

[mack]

Testing

Well just put this back togethera little over a year ago and I cleaned the harness completely at that that time. I'm hoping that the quick turn around may have bound the harness at the yoke and pulled a connection as it went dead
Immediately after. I'm going to pull the headlight and look. Thought I could put a tester in the connectors and check the tach while i was in there, but don't know the numbers to look for.

[bikerphil]

Check the 20A fuse for the turn signals, should be on the same circuit IIRC.

[mack]

So

I go out and turn the key and everything is fine. It starts and the tach is working. So I jump on it and ride about twenty miles, was working fine then all of a sudden it started to miss at the 19.8 mile mark. Went completely dead so I coasted to a stop and went to the main fuse. Sure enough it's blown, put in the replacement and it blows as well as soon as the key is turned.
Wife comes with truck and trailer to recover me, and I get it into the shop.
First thing I figure is that it could be two bad fuses, they were 30 years old, so I convert to the blade style and try it again. Blows that one as well.
So now I have my testers, I check the brown and green from the generator. It's reading 1.6. So I try to check the three whites and I'm getting .8
I check the other bikes and the three whites give me .8 but the brown and green read 3.8 . So I know I have a problem there, but why is it blowing the main fuse. Why didn't the battery just die and and kill the motor, without blowing the main fuse?

[crazy steve]

.....So now I have my testers, I check the brown and green from the generator. It's reading 1.6. So I try to check the three whites and I'm getting .8
I check the other bikes and the three whites give me .8 but the brown and green read 3.8 . So I know I have a problem there, but why is it blowing the main fuse. Why didn't the battery just die and and kill the motor, without blowing the main fuse?

The field coil gets it's power off the brown wire which is the main power from the switch and is protected by the main fuse. If it's internally shorted (which it sounds like it is), it can draw too much power. Also check those two wires to ground; if they're both open to ground, chances are good it took out the regulator too...

[mack]

Grounds

The two blacks at the regulator are solid and so is the ground at the frame under the side cover lock, the negative to frame was solid as well. Any place else I should look?
Funny that the tach started working on it's own, and worked right up until the motor died. If the tach and field coil share a wire, you'd think that if one or the other was bad, both wouldn't work.

[crazy steve]

I think you misunderstood me; check the resistance of the brown and green wires to ground. Do this with the field coil unplugged from the harness at the first plug, not at the regulator. They should both read open, if they don't the coil is bad or the coil wiring leads are. Also check between the green and brown again at the same plug; if you again get the same 1.6 ohm, it's the field coil. If it now checks good (4 ohms +/-), the problem is in the brown wire from the switch to the fuse panel.

Funny that the tach started working on it's own, and worked right up until the motor died. If the tach and field coil share a wire, you'd think that if one or the other was bad, both wouldn't work.

The tach gets it's signal from the other coil; the stator. There is no direct connection to the field coil except for supply power (the brown wire) but every circuit on the bike is fed from that wire... but if the field coil (or it's wiring) has failed, you'll get no output from the stator and the tach won't read.

Also try installing a new main fuse with all other fuses removed and the field coil and regulator unplugged. If it still blows, you have a short in the red or brown wires. If it blows with the key off, it's the red wire. Only blows with key on, it's the brown. You'll probably have to split the harness to find either of these....

[DAVINCI]

Here's a wacky situation for you. I had the exact problem 2 yrs ago. I would lose the tach seemingly for no reason. Turned out the footbrake switch had an internal short, it had overheated. When I applied the brake, it grounded the brown and blew the fuse.

Worth a look.

[mack]

Voodoo

Oh man, the wiring in these things are like voodoo. I can't imagine how many hours it's taken for guys like steve or tony to figure out what goes where and what happens if this or that occurs. We are extremely lucky to have people like this on the site.
I will try to track this down and get back to the forum on what it actually was.
I'm going to kill a chicken now and hang it over the front door to satisfy the demons before I enter my shop.

[crazy steve]

One of these days when I get enough spare time, I'll write up a detailed 'how-to' to check for stuff like this...

Basically, the key to troubleshooting wiring glitches like this (other than poor connections) is to isolate the offending circuit, then continue to isolate it's parts until you find the problem. Where it can get complicated is most wiring harnesses will 'share' some wires among different circuits (to save money is the usual reason) and a problem on one circuit can 'bleed' over into another circuit making you think you have multiple issues. This is where isolating the various 'parts' can clear it up. And there is a specific 'logic' to doing this, but understanding why some of these happen the way they do does require a fairly good knowledge of electrical theory. But luckily, you don't need this to troubleshoot it, only if you have a burning desire to know why it did what it did...

[mack]

Found it.

Did all the checks and knew I had a problem. Pulled the alternaer cover off and looked closely at the wire's , the field coil had a very large slice through it in one spot with bare wires exposed and it looks like it had rubbed some in another.
Question though, I've never seen the result of a fried coil before so excuse me if this sounds stupid. When I looked into the cover, everything is coated with a fine red dust and there is alot of metal filings stuck to the wall of the cover and inside the motor housing. Is this what you'd expect?
The stator is also covered with the dust. I still only read .8 on it same as the other bikes, can this be cleaned and the contact's polished or should I replace it as well?
Your probably right Steve the regulator is most likely fried too. But I still have the original so I can put it back on no problem.
If this doesn't sound normal, I can take some pictures.

[crazy steve]

Question though, I've never seen the result of a fried coil before so excuse me if this sounds stupid. When I looked into the cover, everything is coated with a fine red dust and there is alot of metal filings stuck to the wall of the cover and inside the motor housing. Is this what you'd expect?
The stator is also covered with the dust. I still only read .8 on it same as the other bikes, can this be cleaned and the contact's polished or should I replace it as well?
Your probably right Steve the regulator is most likely fried too. But I still have the original so I can put it back on no problem.
If this doesn't sound normal, I can take some pictures.

Metal filings are bad.... maybe very bad.

There shouldn't be any metal-to-metal contact in there, if there has been you need to try to find out why. The alternator/cover is indexed to the motor case with a couple of dowel sleeves, make sure those are in place and not damaged or bent. Make sure the bolts that hold the stator to the cover are all there. If one/both coils have been removed from the cover, make sure that both are fully seated into the cover; there's close-tolerance 'seats' that these fit into that can be a bit tricky to engage and if you 'miss' the coil(s) can be 'cocked' in the cover.

If all that checks out, check the rotor for runout. I couldn't find a spec for this, but I suspect that anything more than .005" is bad. Possible bent/damaged crankshaft...

One other possible cause; the rotor can end up slightly magnetic, and maybe a metal bit was stuck to it when you reassembled the alternator. If something like this got loose in there, this is the damage I'd expect to see... that would explain the field coil; and see above about the rotor.

As to the stator, it really should read .4 ohm between the white wires, but that may be your meter if you're getting the same reading on other bikes and the charging systems are working. If it checks good, reuse it.

[mack]

Look here

Here are a couple of pictures.


This one shows the filings and the split in the wire. But check out the next one. It's the field coil and the wire was fried just inside the rubber housing plug. The coil itself was so badly burned that it split in half and you can spin the two surfaces against each other.

[crazy steve]

Yeah, those filings in there aren't normal at all. The stator looks ok, but the field coil is toast....

The 'rust dust' is normal. I really suspect something was stuck to the rotor when it was assembled and it finally got into the 'works'....