Where the number lives
Generac air-cooled standby (Nexus, Evolution, Sync): open the lid and look at the controller face or the silver label on the side of the control panel. You want the assembly number (formats like 0H6680D or 0J8371) — not the engine or alternator serial. The assembly number is the orderable part; the numbers stamped on the engine block identify the motor, not the electronics.
Kohler (APM402, DEC3+, MPAC): the number is on a white barcoded label on the controller board itself (e.g. GM104661, GM35950). Photograph it straight-on; Kohler characters like 0/O and 1/I are easy to misread. If the board is already removed, check the anti-static bag or the work order — installers often transcribe the number there.
Cummins Onan RV generators: check the spec plate on the generator housing (model + spec letter) and the control board label inside the access door. Both matter — Onan revises boards across spec letters, so a board that fits spec C may not fit spec G on the same model.
- Generac: controller face or silver panel label — assembly number (0H6680D format).
- Kohler: white barcode label on the board — GM number (GM104661 format), photograph straight-on.
- Onan: housing spec plate (model + spec letter) AND the board label inside the access door.
- Never order from the engine serial alone — it does not identify the controller revision.
Match revision letters exactly
A trailing letter is a different part. 0H6680A, 0H6680B, and the 0H6680D service replacement kit are related but not interchangeable without the documented upgrade path. When a manufacturer supersedes a board, the listing will say which legacy numbers it replaces — read that line before checkout.
In our search, dashes, spaces, and capitalization are optional: "0H6680-D", "0h6680d", and "0H6680D" all resolve to the same MPN page. The search normalizes punctuation, but the revision letter itself must match — D is not B.
Label-photo checklist (3 photos that end guesswork)
Photograph the board front and back, note wire colors and connector pin counts, and pull the generator model + serial from the housing plate. Send all three to a parts specialist — board-only identification fails most often on heat-damaged labels where one character is gone.
Take the label photo straight-on in daylight with the flash off: barcode labels wash out under flash and angled shots make 0/O and 1/I unreadable. Include a second wider shot showing where the board sits so the harness and mounting confirm the family.
- Photo 1: board label straight-on, daylight, no flash — every character readable.
- Photo 2: board installed, showing harness connectors and mounting points.
- Photo 3: generator housing data plate — model, serial, and spec letter.
- Note: wire colors, connector pin count (e.g. 46-pin vs 36-pin Generac), and any adapter harness.
Supersessions: when the old number is discontinued
Manufacturers replace boards without changing the generator name. A legacy board like 0H6680A or 0H6680B is typically replaced by a service kit (e.g. the 0H6680D-series kit) that bundles the board with an adapter harness or firmware note. The kit is the correct order — not a used original pulled from a scrapped unit.
Before checkout, confirm two lines on the product page: which legacy numbers the kit replaces, and which controller families it fits. If either line is missing for your board, send the three photos above instead of guessing.
Failures that mimic a dead board
Half the "dead controller" calls we see are power or sensing problems upstream of the board. A standby battery below 12.4V at rest causes crank-no-start and controller brownouts that look exactly like board failure — load-test the battery before condemning electronics. Corroded battery cables, a blown 7.5A control fuse, and tripped GFCI on the charger circuit each produce a dark controller with a healthy board behind it.
Sensor faults are the second mimic. Low oil pressure switch faults, overcrank from stale fuel, and RPM-sense loss each throw controller alarms that read like board failure but clear once the underlying condition is fixed. Read the alarm history on the controller display first: a board that displays alarms is a board that is largely working.
- Load-test the battery at rest and during crank — surface voltage lies.
- Pull the alarm history before clearing anything; the code names the subsystem.
- Check fuel age on portables: stale gasoline causes overcrank codes on good boards.
When the new board arrives: install without damage
Control boards die most often during installation, not operation. Work with the generator breaker off and the battery disconnected, ground yourself before touching the board, and keep it in the anti-static bag until the mounting screws are ready. Photograph every connector before unplugging the old board — Generac and Kohler harnesses allow several connectors to reach the wrong header.
Seat connectors fully until latches click, then reconnect the battery and power up without starting: the controller should boot to its setup or standby screen. If it does not boot, power down and recheck seating before assuming a defective board — unseated ribbon connectors cause most "dead on arrival" reports, and powered-on boards cannot be returned as new.
- Breaker off, battery disconnected, board grounded-handled and kept bagged until mounting.
- Every connector photographed before removal; latched fully on reassembly.
- Power-up test without starting first — confirm boot screen before cranking.
- Record install date and keep the old board labeled until the new one proves out.
Maintenance parts that prevent controller faults
Controllers get blamed for failures caused by neglected maintenance parts. Stale fuel varnishes carburetor jets and causes the overcrank alarms that look like board faults — a fuel stabilizer routine and annual filter changes prevent most of them. Likewise, a clogged air filter leans the mixture until the controller logs RPM-sense loss, and corroded spark plugs cause misfire codes on an otherwise healthy ignition circuit.
Keep a maintenance kit per generator: air filter, oil filter, spark plugs, fuel filter, and a spare control fuse of the exact amperage. The kit costs less than a single misdiagnosed board order, and the fuse alone resolves a surprising share of dark-controller calls — always check the fuse with a meter rather than by eye, since hairline breaks hide inside the glass.
- One maintenance kit per generator: filters, plugs, fuel treatment, spare control fuse.
- Fuses tested with a meter, never by eye — hairline breaks hide in the glass.
- Battery load-tested spring and fall; cables cleaned and torqued.
Ordering checklist
Run this list before you pay: MPN copied character-for-character from the label, revision letter matched, harness pin count confirmed against the listing photos, and generator model + serial recorded for the RMA record. Orders placed before 2 PM ET ship the same business day, and freight over $300 ships free.
- MPN matches the label exactly, including the trailing revision letter.
- Harness connector and pin count match the listing photos.
- Generator model + serial saved for your records and any RMA.
- Control boards stay sealed in the anti-static bag until install — powered-on boards cannot be returned as new.