Headlight drawing too much current?

Yesterday I rode for about 3 hours and she rode like a dream. Only problem was the headlight didn't work. Then today I go to start her up and I fiddle with one of the fuses and voila, headlamp works again. But then the bike ran like absolute crap, pretty much on one cylinder.

I think what happens is, the battery (12v4a liquid cell) is below the voltage required to kick the headlamp relay, so the bike runs well. Then as soon as I get her over 3k rpm she suddenly stalls on me and I think it's because the light turns on and draws a ton of current.

The electrical on this thing is a major pain. The wires get really hot and I think one of the fuse beds melted at one point in the bikes life. There's a 15amp fuse in the headlamp, a 25 in the main, 20 in ignition and another 25 in the turn signals I believe. Is this correct? Does my situation sound familiar to anyone?

I am firm believer that if your Stator hasn't gone out, its going to. Factoid, its not the stator that went out. its the Wire from the stator to the harness. Since you haven't stated anything specific as far a multimeter readings, you going have to pull out you multimeter, an start checking all the above. Since my bias is bad wires, I strongly suspect if you look on the left side your engine, under and behind the chain. you will see 2 wire bundles running up to the battery box area. If you "gingerly" touch those wire where i comes out from hiding behind the cover, before it bends upward towards the battery. That space right there creates a brittle wire. maybe its the heat of the crankcase that affects it,or the 3 phase stator that makes that point really brittle. so brittle, that it will stop allowing adequate power to pass.

To answer your question I have 1 20, 3 10amps. I have created a photo album with my fuse block upgrade.


So to re-cap Multimeter, find out if your battery is charging appropriate over 12.5 volts at 2k rpm. If not, check Voltage regulator, Rectifier. in above pic, I replaced the voltage regulator. After I repaired the shot wires from the stator. Stator was fine, (Double check, and a prove it first per the manual.) Double check everything per the manual first.

if you find the brittle wires, Go straight to Drewpys Re-Wire, and follow his segment for just the stator. There are other ones, I like drewpies the best.

Like you said there is a relay, but that relay is suppose to keep the headlight off till the stator is creating energy, then it pop's open to send energy to the headlight. Its dumb, cause it doesn't turn it off when the engine is not running, and the key is still in the on position. (Ce-la vie) I wouldn't worry about this stuff untill your sure about the rest. battery charging, Rectifer, regulator, bad wires, Good ground, There is a diode on top of the frame to support head light function. if that went bad, That could be force-ing all the energy to go though the loom, to the headlight, overheating things too.
http://www.partzilla.com/parts/search/Yamaha/Motorcycle/1981/XS400SH/ELECTRICAL+1/parts.html
Part 28, 3H5-81980-00-00 DIODE ASSY
All this does is take a phase and send it to the headlight, so that the other 2 phases can take care of the rest of the bike. (each white wire is a phase, 3 phase electrical system the White wires are AC current till its gets to the Diode, or to the Rectifier. Check the connectors, use a small piece of sandpaper to freshen up the connectors, and blades. if you have a dialectic grease, cover each of them with a dab.
Use the manual for all troubleshooting testing.
Sorry for being long winded. (not really I like this topic, just don't take my word blindly look and double check via google, and youtube)

Yea, you should definitely check the harness diode. if that goes out all kinds of problems could occur with the bike. it has a wide range of problems. Im going thru that right now my self. good luck!!!

, If he didn't have this running in 2013, then I am thinking He gave his bike away. How are you doing?
Tobie

skintech said:

Yea, you should definitely check the harness diode. if that goes out all kinds of problems could occur with the bike. it has a wide range of problems. Im going thru that right now my self. good luck!!!

Click to expand...

what does the harness diode look like and where is it???

Photo here of a repaired diode:
http://www.xs400.com/threads/igintion-problem.12490/page-8#post-134095
Stock looks about the same but the diode is a little white/blue ball.