I am riding home from work last night...it's 8pm-dark...and I switch on my bright headlight and notice -after a few min - that the light is dimming with a quickness...about 10-15%...then slowly regaining brightness over about 4-5 seconds. Then it repeats that sequence every 30 seconds or so. I turned off the spot lamps, tried the low beam only...same sequence of events occured. After about 15 min of riding I think it stopped and lights were as normal. Sat in the driveway with lights aimed at the garage door for a couple of min and didn't notice the dimming occurring. Could this be a regulator issue? Battery is only 18 months old and well maintained.
03 Anniversary RK Classic w/27K miles.

 

It could be as simple as a bad Hi/Low headlight switch. You need to first check the voltage across the battery with a meter when this happens to see if the meter is following (going up & down) when the headlight brightness goes up and down. Most likely is Not the charging system and is something simple like the Hi/Low switch, bulb socket, fuse socket for the headlight etc. Eliminate the charging system by doing the simple voltmeter check first.

 

Thanks for the tech tip. Am suspecting the bulb or socket might be the culprit. I don't think the other front running lamps were dimming and tried to notice if the speedometer light or high beam blue light were dimming but don't think they were.

 

Is the headlight grounded to the chassis? If it is only grounded to the triple trees or housing then that could be your culprit. While riding the neck bearings are moving causing your headlamp to lose its ground. This is ONLY if headlamp doesn't have a separate ground to chassis. You can run an extra wire from headamp housing to a bolt on the chassis pretty easily and see if this takes care of your problem. I've seen headlamp plugs basically melted because of a bad ground.

 

Well it's a bit over a month since I first noticed this problem...and it's been too cold, wet, icy or snow covered to ride around here until yesterday. So I'm taking advantage of the 70 degree days we're having this week and riding to work. I've diagnosed everything I can think of. Bulb and socket are good, ground is good, fully charged battery.

But here's a new bit of diagnostic info;

The headlight, tail light, and front and rear fender running lights are all dimming. But i doesn't look like the speedo light, the high beam blue light, or the front spot lights are affected. And, today I found that if I rev the engine up to around 4000 rpm (bike on side stand, in neutral) the lights all quickly dim for just a moment, then return to normal, but the return to normal is not sudden like the dimming, it's a gradual increase in brightness over a few seconds. Idle and low RPM lights are not affected.
So it has something to do with higher RPMs, which explains the connection to it happening on the open road but not at idle in the garage.

Backtracking: The only thing that has changed on this bike in the past year is changing out the header pipes and replacing a broken front spot lamp which was repaced with a different brand, different lense, but basically the same lamp.

Gonna try Jackie999s voltmeter/battery test tonight.

 

Have a real close look at the battery connections, a little loose or a bit of corrosion will mess things up. Also check your main ground behind the rear cylinder, the Allen head bolt may need to retorqued. One last thing, have you had the regulator off ? I have seen them installed with the harness pinched. Good luck.

 

Thanks for the tips. I will do all that tonight. Also am going to talk to the service tech who installed the header pipes for me. Wondering if he may have moved, disconnected, unplugged any electrical while installing the pipes to help improve access in the tight areas. And with that in mind, the main ground behind the rear cylinder could be a good place to check for connection issues.

 

Well heck. I put the multimeter to the system last night and everything checked out fine. Battery and regulator show no issues.
The battery cable connections looked ok but with a hands on wiggle I found the negative side to be just a bit loose. So I tightened it up...it took a surprising amount of tightening before it snugged up. Did the same to the positive side and after that I could not get the bike to repeat the problem, either in the garage or on the road. I took it out on the backroads around our place for a 10 mile test ride and the electrical system didn't hiccup even once. It looks like that was the problem. Duh! Sometimes it's the simplest thing that gets overlooked.
TFTCAR...your suggestion to check the cables turned out to be a wise one!

 

A harley runs off the battery and the charging system just charges the battery. Battery connections are very important on them