A mounting system attaches directly to a square or round trigger guard of a firearm. A separate trigger guard mount assembly includes a base having a groove formed therein for receiving a forward portion of a trigger guard of the firearm. A trigger guard mount clamp for attaches the trigger guard mount base to the forward portion of a trigger guard. A screw-operated clamp removably attaches a light housing assembly to the trigger guard mount assembly where the light housing contains a laser light source or a light bulb. A dovetail is formed on the trigger guard mount base to engage a dovetailed slot on the light housing, where the dovetailed slot is adjustable in width for releasably capturing the dovetail of the trigger guard mount base. The trigger guard mount assembly also includes set screws for fixing the trigger guard mount assembly in position on the forward portion of the trigger guard of the firearm. One or more shims are contained within the groove of the trigger guard mounting assembly. The shims have various thicknesses to compensate for the widths of the trigger guard of the various firearms. The trigger guard mount base and the trigger guard mount clamp are held together with a self-tapping screw.