What the start solenoid actually does

The pump motor pulls 150–300 amps under load — far too much for any switch or remote to carry. The start solenoid is a heavy-duty relay: your pendant or wireless remote sends a small trigger signal to the solenoid's coil, the coil snaps an internal contact closed, and full battery current flows to the motor. The remote never touches motor current. That's why a bad or missing wire on either side of the solenoid kills the whole system even when the remote lights up fine.

The wiring at a glance

Fig. A-5 — KTI’s official wiring diagram. Battery (+) → start solenoid → motor (+), with grounds returning from the motor and the solenoid body. Pendant wires: red = UP (round-coil directional valve), green = DOWN (square-coil load-holding valve — double-acting units), grey = ground; black/white feed the pendant. Note how many separate ground wires there are — every one of them matters.

Simplified schematic of the same circuit — heavy red = positive path, heavy dark = ground path, dashed blue = remote trigger (signal only).

Fig. A-6 — Where things live on the unit: the start solenoid is the small cylinder mounted on the DC motor with two large copper studs.

Fig. A-3 — The (−) ground terminal is the 5/16" stud on the motor body. This is where your ground cable attaches — not the mounting bolts, not the trailer frame.

Wiring it, step by step

1. Disconnect the battery Pull the negative terminal off the battery before touching anything. The positive cable you're about to run is always hot once connected.
2. Identify the solenoid's two large studs One stud goes to the battery; the other already has the short factory cable running to the motor. Never move the factory cable — if both large studs are empty, the battery stud is the one facing away from the motor.
3. Run the positive cable 2 AWG welding or battery cable from battery positive to the solenoid's battery stud. Put a 150A fuse or breaker within 18" of the battery. Torque the stud nut snug over the ring terminal — hand-tight backs off from vibration.
4. Run the ground cable — same gauge, battery direct 2 AWG from the motor's 5/16" ground stud (Fig. A-3) straight back to battery negative. Don't ground to the trailer frame through paint and hope — the motor needs a return path as heavy as the feed.
5. Connect the remote Wired pendant: plug it into the harness connector on the unit. Wireless: see our KWR wireless remote install guide. The trigger wire lands on the solenoid's small coil terminal — it carries almost no current, so light-gauge wire is fine here.
6. Reconnect the battery and test empty Battery negative back on last. Press UP with the bed empty — you should hear one solid click from the solenoid and the motor should spin immediately.

The ground: read this before you call the pump dead

Almost every "brand-new pump / replacement motor won't do anything" call we take turns out to be the ground. It's easy to see why: the positive cable is obvious — big, red, goes to the battery. The ground looks optional because the pump is bolted to a steel trailer. It isn't optional. Mounting bolts pass through painted, powder-coated, or rusty surfaces that conduct poorly or not at all.

• No ground at all → total silence. No click, no crank. The remote may still light up (it draws its trigger power elsewhere).
• Weak ground (frame paint, loose bolt) → solenoid clicks but the motor won't spin, or the motor drags and lifts painfully slow under load.
• The fix → dedicated 2 AWG cable, motor ground stud → battery negative. If you must use the frame, grind to bright bare metal and use a star washer under the lug.

Troubleshooting by symptom

Common questions