ground terminal 104 transistor 118 is turned on by a pump signal flowing through diode 121 and resistor 126 to the base of transistor 118 indicating that the circulating pump is circulating fluid between the solar collector pipes 26 and the storage tank motion limit control circuit 48 is similar to circuit 59 but it has no provision for reacting to high temperature defocus or pump signals circuit 48 passes signals from amplifier 46 through diode 57 to motor power control 52 unless the reverse limit is reached and reverse limit switch 58 has opened motor power control 52 as shown in fig8 includes a differential amplifier 127 six npn transistors q1 q6 two diodes 128 and 129 a capacitor 131 and thirteen resistors 132 144 resistors 144 and 135 are serially connected as a voltage divider between the positive twelve volt source 105 and ground terminal 104 the inverting input terminal 145 of amplifier 127 is connected to the junction between resistors 135 and 144 the cathodes of diodes 56 and 57 also shown in fig5 are connected through serially arranged diode 128 and resistors 138 and 140 to the non inverting input terminal 146 of amplifier 127 resistor 139 and diode 129 are serially connected in parallel with resistor 140 with the cathode of diode 129 connected to terminal 146 capacitor 131 is connected between terminal 146 and ground terminal 104 all six transistors q1 q6 have their emitters connected to ground terminal 104 transistor q1 has its collector connected through a motor drive relay.