ECM- RACEWY6 electrical housing can hold up to 6 ETA-ECM20/ETA-ECM20M modules, use less than 6 modules. Open slot on ECM-RACEWY6 can be covered up using an ECM module blank plate cover. Two of these are included with ECM-RACEWY6. If not needed, discard them. If additional blank plates are required they can be purchased in packages of three.