Hi, I have an 87 softail that has had an electrical issue since i got it. When ever i turn on the headlight the amps drop and it runs real rough, the closest thing i can equate it to is when you have a car running with real bad timing. It still runs but the power drops a lot and it backfires when you throttle off. If i turn the headlights off it runs perfectly again, also even during the day when im riding sometimes when i indicate i can feel the power drain every time the indicator blinks on. I have replaced the coil, stator, battery, entire wiring loom (including handle bar wiring), regulator. What else is there to check? Its driving me crazy and im getting kinda sick off pouring money into things that arent faulty. Any advice would be greatly appreciated. Cheers

Motorhead, i replaced the ignition switch with the loom but cant remember if the circuit breaker was also done. I will check. How does this explain the mementary power drain when just the indicator is turning on and off though as the headlights arent on at all. ps i have kept all my old stuff.

 Haha sorry Dave, Im a big Motorhead fan actually, Lemmy is the man. But back to the issue, yes everything works fine when the engine is off. If i try to start it with the headlights on it backfires and is hard to start, headlights off and it starts first turn everytime. When i start it i have to get into second gear and turn the headlights on and there is a pause of about a full second where the motor is off and then it kicks back into life with a pop (backfire) and runs rough. If i pull the clutch in and let it idle for a second while rolling and then give the throtle a couple of small twists it sometimes comes good and runs as it should but as soon as i have to indicate or brake it imediately returns to rough as guts. It seems the amps are only just at 32 or slightly below and the extra draw of a headlight and/or indicator/braklight is enough to push it over the edge and feels like its running under load. The only thing i havnt changed is the ignition module, could this have anything to do with it??

I'll be betting it's a loose connection somewhere.
Start with the earth connection on the battery.
Next, anything with a plug and socket.
After that, switches etc.
Then, look for kinks or corrosion in wires.

I bet when you find it it will be something simple.

 

 Check all your earth connections  Eddy, could possibley be, and sounds like a classic earth feedback problem.

(the lighting circuit has a bad earth so it's feeding back through the path of least resistance, the ignition circuit to earth)

 

If ya wanna check fast if it is an earthing problem, just hook up a jumper lead from a good section of the earth circuit in the wiring harness and earth it out to a good connection on both the frame and battery negative terminal.  Then try things.

mmm ive never rewired a bike an used circut breakers cant see em when they are stuffed i run fuse box where the ign module goes on the ol evos

mate bike had similar prob an ihis was in the breakers so replaced with the fuse setup ...now this may sound stoopid to some but have a good look where ya wiring runs ive had bikes that when ya hit a bump itd die then go ok again could be something is either crushed or earthin out in the harness if in doubt check every wire an i mean every wire have a bikky or beer grab a seat when ya missus is out tune some tunes on an start checkin

my first harley in 75 was a 56 pan an every time i put knee on seat to kik her ova wouldnt start but if i didnt touch seat away she go found one wire which was gettin crushed an shorting the bike out so i left it as mty anti theft device

Alternator last time i had a problem like that

I'm thinking earth as well as when he pulls the clutch in the bike is getting earth through the cable and comes good. Check the main cable from battery to earth.

The frame could have been powder coated so the engine is not earthing to the frame. Easy fix would be piggy back a extra earth wire from engine earth to a clean frame bolt.

Buy a cheap multi meter from dick smiths or Tandy for $15 and check all the earth wires. Red on battery positive and the black wire to all earth connections check for 12 volts. If you find a dead earth there's your problem.
Good luck.