Maintain your battery and light your charging system!
9 times out of 10 the reason why your bike will not start is usually because of the battery condition or loose connections. A charging system failure is less likely but is still possible.
I will talk about both of them here.
First look at your battery connections. Check for obvious and easiest to fix problems first. A loose connection, poor ground etc. will likely cause intermittent operation 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 little grease to the contact points. The grease helps to prevent any of the white corrosion residues building 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. 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. Notice I say, "may" here because the bike's charging system 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 can not add water to a maintenance free battery) Charge the battery overnight with a slow charger only. Motorcycle batteries can not 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 will not go buy a new battery and your problem 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 engine running, place the multimeter leads on the battery. Rev the engine a little. The system voltage should rise with engine RPM. A voltage of around 13.5 to about 14.5 should be displayed. If the voltage lasts constant and / or is slowly decreasing, or if the voltage increases above 14.7 volts the charging system is not functioning.
What do you do now? You have to check two things. The Stator and the Regulator. The statator creates an AC voltage. The regulator changes the AC to DC voltage and also maintains that voltage at the proper level.
The Stator can be checked with the Ohms function on your meter. Locate and remove the plug for the stator on the front of the engine block. You will see two or three pins inside.
Set the meter for low Ohms, and measure the continuity between these pins. 5 Ohms or less is what you are looking for here. Set the meter to the highest 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 not be opened. Replace the regulator if everything else on the charging system checks out or if there is an overcharging situation.
On most Harley's you will not know if the charging system is beginning to fail. The evidence shows up when you have dim lights or she just will not start. There are aftermarket accessories that you can install on your bike that will tell you the current state of the charging system.
Save yourself some bucks here !! With a simple multimeter available from any Electronics parts store you can troubleshoot your charging system and check your battery and most likely repair any problems yourself.
Source by Keith Nivon