That relay might be a dual form A, the rare one used in the headlight circuit. To verify, check continuity between 30 and either of the 87s. If none, then set that relay aside and look for one with 87a and test it the same way. You're looking for continuity between 30 and some other pin as the normally closed contact.

The coil is the load your float switch is going to send power to. Most relays, it won't matter which side, 85 or 86 is the positive side, but some have flyback diodes internal wired across the coil, so the convention is to use the relay with terminal 86 toward the battery +. See the Wikipedia on din 72552, but don't let it stand in your way on the other terminal designation.
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Art Benstein near Baltimore

Q: Do you know how an electrician tells if he's working with AC or DC power?

A: If it's AC, his teeth chatter when he grabs the conductors. If it's DC, they just clamp together.