Dead cart
fault tree

• Battery pack / BMS — under the seat. On a lithium retrofit, the two heavy cables leaving the pack are the ones that matter; everything downstream hangs off them.
• Tow/Run switch — under the seat, near the controller. In TOW the whole control circuit is dead by design.
• Solenoid — under the seat on the controller plate. Two big lugs (pack power in, controller power out) and two small terminals (the coil).
• Controller — the finned aluminum box on the same plate. B+ and B− are the heavy terminals, M− (or A2) feeds the motor.
• OBC (onboard computer) — small black box near the charging receptacle. Lead-acid-era part; it draws current around the clock.
• MCOR — behind the accelerator pedal, under the floor mat and access panel. Has a 2-pin connector (microswitch) and a 3-pin connector (potentiometer).
• F/R switch — on the dash or under the seat depending on trim.
• 15 A control fuse — in the harness near the OBC.

The solenoid clicked, so the whole interlock chain — key, Tow/Run, F/R, MCOR microswitch, controller driver — was working at that instant. The cart moved, so the controller and motor produced torque. Then everything went away and won't come back.

That sequence describes power being cut at the source mid-draw, not a switch or sensor failing. On a lithium conversion the source has a brain: the BMS. When it opens its discharge path, the cart goes from "almost worked" to "totally dead" in one step, which is exactly what you saw.

With this specific pack the cause is easy to name. The BMS allows 200 A for ten seconds and nothing more. Two weeks of parasitic draw brought the pack down toward its 40 V floor, and then the empty controller capacitor bank plus the launch load pulled well past 200 A the moment the solenoid closed. The BMS read that as an overcurrent event and latched off. Page 2 of the display confirms it in about thirty seconds.

• Page 1 — Real-time. State of charge as a percentage, pack voltage, current draw, temperature, and time-to-empty. Voltage is the number that matters here. Current is worth watching while someone else presses the pedal: if you see it spike toward 200 A on a launch, you've watched the fault happen live.
• Page 2 — Battery switch. DSC and CHC toggles for discharge and charge, plus max/min temperature, cycle count, and a status field that reads NORMAL when the BMS is happy. This is the page that diagnoses your cart. DSC OFF means the pack cut its own output. You can also toggle discharge back on from here.
• Page 3 — Cell voltage. All sixteen cells in millivolts. Rested they should read roughly 3200–3400 mV each. Right off the charger they'll read higher — the factory screenshot shows around 3700 mV, which is a full pack, not a fault. What matters is the spread: more than about 100 mV between highest and lowest means the pack wants a long balance charge, and a single cell far below the others means a real problem.

• Precharge resistor. Roughly 100–200 Ω at 10–25 W wired across the solenoid's two large lugs. It lets the controller caps fill gently before the solenoid slams closed, which stops the inrush trip and stops the solenoid contacts from arc-pitting themselves to death. Most drop-in kits don't include one and most installers skip it.
• OBC. It was designed to manage lead-acid charging and it sips current continuously. On lithium it does nothing useful and it's a prime suspect for walking a pack down during storage. Bypass or remove it per your pack maker's instructions.
• Main disconnect. A battery cutoff switch on the pack positive, thrown whenever the cart sits more than a few days.
• Storage charge. Park it around 50–60%, not empty. Lithium doesn't like sitting near the bottom of its range and that's where the BMS trips live.
• Charge the pack every few weeks if you can't add a disconnect.