In the fuse pannel which is below your headlight switch, check your manual as to which exact fuse it is, there may even be a diagram on the bottom of your dash if you don't have your manual.
Only the 2.3L HSC Inline 4 will fit in the 1986 Mercury Topaz. If everything in the engine bay were gutted, perhaps something larger such as a 3.0L V6 from a 1992-1994 model MIGHT fit but it would require a complete running 92-94 Ford Tempo or Mercury Topaz with the V6 engine as a donor car (and, if you could find such a car, it would be more worth your time/money to invest in it v.s. a 1986 model). The automatic transmission from a Taurus WILL NOT WORK in a Tempo/Topaz.