When power is applied to the relay coil, a magnetic field is created and
energy is stored in the coil. When power is removed, the magnetic field
collapses causing a reverse voltage to be generated (it's called inductive
kickback or back EMF). The back EMF can easily reach 200 volts.
The diode will absorb the reverse voltage spike. This voltage, if not absorbed
by the diode, will cause premature failure of switch contacts or
feed back to other crucial vehicle electrical parts.
Side Mount Bracket