Make sure all connections are tight, battery, altenator and engine ground wire is tight. Then connect a 12 volt tester on the battery and check battery voltage, should be 12.75 or higher, then start motor and recheck voltage should be higher, rev engine should raise and settle. If it only maintains battery voltage or less, need to replace diodes or altenator. If you have a voltage regulator check there too! As it will control altenator.