That looks like the starter relay. Is that correct?
If so, then you should
always have only ONE wire that is switched by the relay.
Therefore, the other wires would connect to the side with the battery wire.
Do you have a mini/new starter upgrade? Is that why you have TWO wires that are
switched by the relay?
If so, that is a VERY VERY bad idea. Like walking blind-folded across a street, that "may work for a while". But, do it enough times, and VERY BAD things happen to you.
There are wiring diagrams at:
Mustang FAQ - Wiring & Engine Info
For a mini/new starter install, see:
http://www.fordracingparts.com/download/instructionsheets/FordInstShtM-11000-A50A75B50B75.pdf
From the manual: (Caps and bold are from the manual)
! ! ! WARNING: DO NOT INSTALL A JUMPER WIRE BETWEEN THE BATTERY TERMINAL AND THE
SOLENOID BLADE TERMINAL AT THE STARTER TO AVOID THE USE OF THE # 12 WIRE. IF DONE,
VOLTAGE IS GENERATED TO THE SOLENOID BY THE STARTER SPINNING AFTER THE RELEASE OF THE START KEY OR BUTTON, CAUSING THE STARTER TO REMAIN ENGAGED, RESULTING IN SEVERE DAMAGE AND EVENTUAL FAILURE OF THE STARTER ! ! !
BTW: IMHO,
***BFD*** about ruining a starter!! There's also a
good chance of munging up teeth on the flywheel. What a "fun and cheap" thing to replace - NOT! And, in the absolute worse case, a broken rod/etc could happen from the starter "re-engaging and applying force" as it free spins.
More FRPP manuals at:
Ford Racing Performance Parts - [Downloads]