This new old stock (I have 9 of these available) Blackhawk Part # 87002199, battery charge regulator. High quality battery sensing circuit for 12V Lead-Acid batteries. Monitors battery terminal voltage & switches a relay output when set limit is reached. Relay re-closes on voltage drop to a preset limit to start charging again. Both set points are adjustable on-board. Nice print of the schematic is included. P1 & P2 are the set point trimmers on the board; little black squares with "X" slot. Board contains: LM7808 regulator, LM393 Dual Comparator, 12V DC relay with 30 Amp contact rating. Please e-mail any questions & see my other auctions. I will combine shipping when possible.