Frobenius elements in Galois representations with SLn image

Suppose we have a elliptic curve over a number field whose mod l representation has image isomorphic to SL2(Fl). We present a method to determine Frobenius elements of the associated Galois group which incorporates the linear structure available. We are able to distinguish SLn(Fl)-conjugacy from GLn(Fl)-conjugacy; this can be thought of as being analogous to a result which distinguishes An-conjugacy from Sn-conjugacy when the Galois group is considered as a permutation group.