Maintain your Battery and check your charging system!
9 times out of 10 the imagine why your bike won't start is ordinarily because of the battery condition or loose connections. A charging law failure is less likely but is still possible.
"Voltage Regulate"
I will talk about both of them here.
First look at your battery connections. Check for positive and easiest to fix problems first. A loose connection, poor ground etc. Will likely cause intermittent performance of the starting and charging systems. If you find a loose connection and/or corrosion, clean the connections with a wire brush.
Before re-attaching apply a dinky grease to the palpate points. The grease helps to prevent any of the white corrosion residues construction up around the battery terminals.
Try and start her up now. You still have a problem? Go down to the mall and buy yourself a small electronic multimeter. (Make sure it has both Ac and Dc volt functions, as well as a continuity (or Ohms)function. Pull out the battery and set it on a counter. Set your multimeter to Dc volts. Quantum the Battery voltage by placing the red lead on the positive and the Black on the negative.
The voltage read should be around 12.5 volts (higher is Ok) If the voltage is less than this it may indicate a poor battery. Consideration I say, "may" here because the bike's charging law might be at fault. In this case the battery will most likely be Ok.
Confirm that the electrolyte level in each cell of the battery is good. Add distilled water only to cell's with a low level. (Obviously you cannot add water to a maintenance free battery) charge the battery overnight with a slow charger only. Bicycle batteries cannot handle a fast charge. Make sure the charger only charges at a rate of 2 amps or less.
Install the battery and try and start her again. If she still won't go buy a new battery and your qoute will likely be fixed. If she starts and runs like a charm, then you have to find out why the battery went dead. You need to check the charging system.
With the motor running, place the multimeter leads on the battery. Rev the motor a little. The law voltage should rise with motor Rpm. A voltage of around 13.5 to about 14.5 should be displayed. If the voltage stays constant and/or is gradually decreasing, or if the voltage rises above 14.7 volts the charging law is not functioning.
What do you do now? You have to check two things. The Stator and the Regulator. The stator creates an Ac voltage. The regulator changes the Ac to Dc voltage and also maintains that voltage at the allowable level.
The Stator can be checked with the Ohms function on your meter. Locate and take off the plug for the stator on the front of the motor block. You will see two or three pins inside.
Set the meter for low Ohms, and Quantum the continuity in the middle of these pins. 5 Ohms or less is what you are finding for here. Set the meter to the top setting. With 1 lead attached to a metal part of bike check for continuity to each pin. You meter should read infinite, or no continuity. If these tests check out then your stator is fine. If there is a fault in any of these tests, then see your dealer
The regulator is the easiest of all to check. The regulator is made of solid state electronics and can't be opened. Replace the regulator if everything else on the charging law checks out or if there is an overcharging situation.
On most Harley's you will not know if the charging law is starting to fail. The evidence shows up when you have dim lights or she just won't start. There are aftermarket accessories that you can setup on your bike that will tell you the current state of the charging system.
Save yourself some bucks here!! With a easy multimeter available from any Electronics parts store you can troubleshoot your charging law and check your battery and most likely heal any problems yourself.
My bicycle Won't Start! What Now?