Garnet SeeLevel I 705 Series Manual page 13

To program the sender as top or bottom:
1. Note that for 4 tank models, the gray and galley tanks can only have
single senders, so this section does not apply to them.
2. Since the senders are all connected in parallel to save wiring and to
simplify installation, the senders must be programmed so they know
whether they are a single, top, or bottom sender. This is done with the
tab at the top center of the sender. See the following diagram.
3. The senders default to single or bottom operation if the programming is
not altered. Consequently, if the sender is for single or bottom operation,
nothing further needs to be done to it (beyond programming it for the
correct tank).
4. For a top sender, remove the tab that says "TOP" next to it.
5. This is all that is required to program the senders for single, top, or
bottom use. However, if you make an error, you have one chance to
correct it, as described below.
6. If the "TOP" tab has been removed and it should be a single or bottom
sender, then cut out the recessed top correction tab that says "TC" next
to it. This reverses the effect of the top tab.
7. Verify that both the top and bottom senders have been programmed for
the correct tank.