Your battery pack's high voltage can't run lights, horn, or 12V switches directly — the DC-DC converter steps it down, and the contactor is the heavy-duty switch that safely connects or disconnects pack power. Here's each connection, by function:
1. DC-DC INPUT+ / INPUT− — pack voltage in. Always confirm the input range on the unit's label before powering up.
2. DC-DC 12V OUT+ / GND — regulated 12V out to lights, horn, switches, gauges. Input and output terminals aren't always clearly marked — check the label.
3. CONTACTOR B+ / B− — the main terminals carrying full pack current from battery to controller. Heavy cable, tight connections, no shortcuts.
4. CONTACTOR COIL (A1 / A2) — the small low-voltage signal from the key switch or controller that closes the contactor. Coil polarity varies by brand — check the label.
5. KEY-SWITCH LINE — switched pack voltage that wakes the controller and tells it to close the contactor.
6. FUSE — always a fuse or breaker between the pack and the contactor. Cheapest safety part on the whole build.
Never guess with high-voltage pack wiring — ask someone who knows your specific build. Questions? Bring them by the shop and we'll walk through your build.