Weak and sporaddic electric signal

Maxx650

Maxx650

XS650 Addict
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Hey everyone,

I've come across an electrical issue on my bike, here are the facts:

Firstly, my 1979 xs650 special has recently sat through a couple big showers here in Austin in the past 2 weeks unintentionally, so it has gotten wet but for the most part kept dry after learning of these issues.

  • About 2 weeks ago I had trouble getting my headlamp to come on. I could get it to come on after twisting/squeezing/manipulating one of the couplers (6-wire plug) under the right side cover.
  • About 1 week ago this progressed into affecting main power as well - with key turned, I couldn't not get a neutral light - when I did see a neutral light it was weak, grow/flickered and then eventually went to normal/maximum brightness. I could manipulate same coupler and get in good position. At this point I lost electric start abilities but could kick it.
  • As of this week, my brother (electrical engineer) and I rewired the connection at the coupler thinking that is what was causing the issues. They are now 6 individual plugs.
  • Now the problem persists still. However, I now know that in order to get power/a neutral light I cannot have one of these wires connected (dark green to dark green) - I figured when I was manipulating the coupler I was actually disconnecting the contact of that wire pair, perhaps. I think this may be my headlamp wire as that is a component not coming on when I manage to kick my bike.

Currently I can turn on the key with engine in 'off' position. Wait 5-8 seconds for the neutral light to grow from very dim to its full potential. Then flip switch to run position - sometimes neutral light dims / cuts out and I have to wait / continue toying, sometimes the light stays at full potential. When it's at full potential in run position I can kick start it... When riding it often dies while down shifting, perhaps due to low rpms? I also had some random issues like my left blinker coming on randomly while ridin. Now using the blinker will kill the engine.

I have tried trickle charging and doesn't seem to make a difference. The battery was purchased from mikes about 5 months ago. I'm not really sure if there is a short in my wires or something with my coil or what, I'm pretty lost.

  • Battery measures 13V off and gets up to 13.5 when revving [NOTE: values uncertain.. taken with a crappy multimeter]
  • My fuses don't look blown but when measuring with ignition switch on (not engine running) they only measure like 4-6V across. All measured at 0 ohms so I think not blown.
  • Electric starter only goes "click" before killing the power and I watch the neutral light grow for a few seconds until it gets bright enough to know the bike is getting full power

So.. Anyone know what's up? Alternator? Ignition coil? Reg/rect? I'm lost and you guys are always excellent. Thanks a lot!

Maxx650
 
Last edited:
My EWAG* is you have a bad/intermittent ground. If so you probably got a circuit to close when you wiggled the wires going to/from that connector and it is not closing now that there is no tension on that loom.


*Educated Wild Ass Guess
 
Thanks Burns, I'll check up on ground connections. I took my battery to a nearby Yamaha dealership to test it and they said it was pretty dead, reading about 8v and 0 cranking amps. So I suppose my multimeter is crap and my trickle charger can't get it over a large chunk of voltage loss.

Its charging at the dealership but I won't be able to pick it up until probably Tuesday... So seems like most my issues could be attributed to a dead battery, but I'll need to do some tests on my alternator to see why the battery lost so much charge.
 
Agree with Burns. Especially on these older bikes, often the ground is picked off the headlight bucket, it's mounts, or somewhere on the fork set. The return path to the battery ground in that instance goes throught the steering head bearings, which is pretty lame. Try hooking a jumper cable to the battery, and to the front axle or other bare metal on the forks, and see if your symptoms change. This will tell you if you should check all the grounds and install a bonding strap between the main frame and the front end.
 
Maxx650,
You've checked your brushes? And the resistance between rotor slip rings?
Low battery power will make the lighting wackey.
 
Hello all, thanks so much for your help and suggestions!

I've picked up my battery from a local yamaha motorcycle dealership where they charged it up and did a load test on it.. their diagnosis: battery is crap.

Charged up to 13V but had 0 cranking amps? Anyone else had any trouble with Mike's replacement AGM battery (link)?

I'm not sure if something from my bike/charging system killed it or if I just had a dud.. it's only 3-4 months old so I don't see why it should be failing.. I do wish Mike's had a warranty for a dead new battery.

I'll update with how my symptoms are once I get a good new battery in her.
 
Good news everybody!

My issues are gone! It was indeed my battery that was crap. Honestly I should have load tested it first before I started fixing my wires.. but it was only a few months old and I didn't have any reason to suspect.. atleast my wires are nice and clean now!

I bought a regular-ole' acid filled "Bike Master BB14L-A2" from the yamaha dealership since it was the only place I'd find something local. They filled it up and charged it, I popped it in and right away I had a nice bright neutral light, working blinkers and my electric starter cranked away until it finally started (has been sitting a week or two since these issues).

Bonus: I plugged in the wire I stated that I had to leave unplugged to kick previous to getting this battery and it was indeed my headlamp wire which works perfectly now.

So all my electrical issues chalked up to a bad battery; get yours load tested folks!

As previously asked, anyone else had trouble with Mikes XSs replacement AGM battery for 1979? link

Also, I'm keeping my eye out for reasons why my battery crapped out.. perhaps something faulty with my charging system. I'll be going through Curly's charging guide tomorrow now that I know I have a working battery.
 
'Nother Austinite here. Measure from the + lead disconnected from the battery to ground, with the key off. Should be infinite resistance. If it is, you can leave the battery connected with no worries.

It's been said before, but every single connection on these needs to be gone through before they become reliable. Oftentimes the crimp to the wire will be bad by now. If I was doing it over I'd consider a new harness from Mike's and not worry about it all. You mentioned the blinkers. Deep inside the blinker switch are three solder joints that seem to always need to be redone before the blinkers become reliable.
 
Eh, well... If he can buy one battery he can probably buy two.
 
Maxx650, If you do a bit of searching you will find that yes, those batteries Mike's sells are of questionable quality. Many have gotten bad ones. Mike's has replaced many of them. You might contact them and see if they will do anything.
The 14LA2 battery is pretty common. They can be gotten at many places, even Wal Mart sells a cheap one, Not reccomended, to cheap. Most parts stores, Farm supply stores. Most anyplace that sells batteries.
jd750ace, on the 79 they ran a ground wire from the left side switch housing down into the headlight bucket to the harness ground. This ground path bypassed the steering head bearings. I think they started doing this mid 78.
Leo
 
So, obviously it was a problem before! Cool. Many modern bikes have a dedicated path, but lots of older ones do not.
Thanks Leo.
 
Thanks again for all the help guys.

Now that I have a new battery - my wacky symptoms are gone, but it has become apparent that I have a charging issue (and probably what killed my old battery?).

Bought a new multimeter and went through most of the steps of Curly's Charging guide and I believe I've gotten it down to the regulator/rectifier.

I tested for volt leaks (none), new battery at 12.4 V... only getting up to 12.8 V at 4K rpm. Voltage coming from stator is good after ohms (.4) and AC test (10.5 V from each white-to-white wires). Also made sure to test my ground wire and ground connections and they seem to be fine.

I believe my regulator/rectifier is located directly underneath the battery compartment and is held on with a single nut? Can anyone confirm this? Easiest way to take it off seems to be: remove left side air filter pod and unscrew the nut holding it to battery compartment - should it just drop from there and I can pull it through the side?

I will be testing the reg/rect tomorrow.
 
Finished up the rest of Curly's charging guide and looks like my rectifier is dead. I will be ordering a new one next week and installing... anyone have any suggestions? I was thinking of getting a combined rectifier/regulator as they're not too expensive and I should probably replace my regulator while I'm at it.
 
Maxx650 said:
Finished up the rest of Curly's charging guide and looks like my rectifier is dead. .
Click to expand...

I don't remember if Curly tells you the rect is bad by deduction or if he tells you to measure it. Before you order you can test it directly if you haven't, with a meter as you would test diodes. The manual shows the innards of it.
 
Yes, I did test the diodes (two measurements in both directions) and that's why I think it's dead.. I was reading 25 ohms for the diodes in the 'input' direction to the rectifier but had Ol (infinity) in the other direction.. so I believe the circuit is bad due to this.
 
^From that description it sounds like the rect is in fact good. Each diode should read high one way and low with the probes reversed.
 

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