that is probably the extra unlabeled coil shown up in the search relay area on the schematic. Unfortunately, the picture I have of the back door shows that a largish paper tag should be next to the unit, but the resolution isn't good enough to read it.

since it's on the 17V circuit, tho, it's likely the same as the search relays coils, so see if you can read the number off one of those.

another approach when the paperwork is lacking is to look at the next machine of that type - in this case, show-time.

show-time schem says a similar function/circuit relay is called the #3 safety relay, and it's switch prevents search relay #3 from powering if a button is down - which disables/stops win detection and payout.

that doesn't help with the coil part number. If you can't find a part number on the search relays, yell and hopefully someone can dredge one up.