To answer this question, we looked in the Apple Service Programs binder.
The following information is under the "Product Notices" tab on page
8.4.12 (6/15/89 is the revision date):
Macintosh SE and Macintosh II Third-Party Add-Ons (Announced September 87)
The addition of third-party peripherals does not void the Apple Limited
Warranty, provide that:
- The addition of the third-party peripheral does not require modification
to the design of either the Macintosh II or Macintosh SE.
- If a third-party peripheral requires dealer installation, the
installation is performed by an Apple Service Certified Technician. ESD
precautions should be followed during installation.
- The total number of internal drives does not exceed two for the
Macintosh SE.
- Third-party peripheral cards satisfy Apple specifications for the NuBus
architecture in the Macintosh II and the SE-Bus architecture in the
Macintosh SE.
- Third-party RAM SIMMs must meet Apple specifications for the CPU they
are installed in.
- Third-party hard drives satisfy the thermal, physical, and electronic
specifications stated by Apple for internal SCSI devices.
Based on the statement, "The total number of internal drives does not
exceed two for the Macintosh SE", any Macintosh SE configuration that has
three internal drives voids the Apple Limited Warranty. Also, any
configuration that disrupts the internal thermal dynamics (air flow) of
the Macintosh SE voids the Apple Limited Warranty.