I had posted this in the electrical forum but got no replies. Was wondering if posting here that somebody might be able to help. I have a 2003 FLHT with carbeurator.
I noticed my voltage meter going up and down, up and down, along with my head/spot lights. It did not matter what the rpms were doing other than at idle. While sitting and warming up, the voltage was fine. No fluctuation. When I put it in gear and started up the road, I noticed my lights got real dim then gradually got brighter and brighter then they got dim again and kept doing this all the way home. It was about 40 degrees out. I took it out last weekend in 70 degrees and no problem.I searched the forum but could not locate anything similar. I was wondering if it was just the cold weather.

 

I think I'd start with cleaning the battery post and connectors. How old is your battery? Cooler weather always brings out a weak battery.

 

I had a similar problem with my Super Glide, turns out I had a broken battery cable. The insulation was all that was holding it together, causing it to sometimes lose contact when the engine vibrated. Check it out, could be something as simple as that.

 

Start with battery cables, clean terminals, suspect voltage regulator, then, if all else fails, stator.

 

If all connections are good and bettery is good, I would check the voltage regulator- I had a bad one at 5k

 

I'd have to take a shot with the voltage regulator vote. I had one go out on my '06 road king classic as well. Might be worth sticking a regulator to it.

 

Does your battery hold its charge ? Its normal for the headlight to dim slightly at idle and brightenwhen the rpm's are brought up. The charging system works only above a certain rpm,I would guess 1500 rpm or so. The others have offered good advise, clean tighten and check your battery/cables. Trouble shoot before you buy a regulator, there is no refund on electricial parts.

 

If your battery checks to be good (load test) clean terminals and you still have the problem. Do a volt drop test on the battery cables before you start buying parts.

Connect a voltmeter to each end of the cable and turn the engine over note the reading. The spec should be in the maual. If it is over a volt check the cable.

From what you are discribing your problem is in the battery or cables. More likely the battery.

 

That is the best way to check is with a voltmeter while it doing what you say it is doing.Then you will be able to go right to the problem.Check the battery free voltage before you even start.

 

Thank you all for the advise. I will go over it thoroughly this weekend and let you know what I find out.