1
3
5 3 4
 6
5
5 3 4 4 5
3
1 1 1
5
4 4 3 4 4
5
5 5 4 3 2
3
1 1 2
5
5 4 3 5 5
 1
3
10 1 5

1
 1
-1
2
2
3
1
 1

t = int(input())
for _ in range(t):
    n = int(input())
    A =list(map(int, input().split()))
    if min(A) == max(A):
        print(-1)
    else:
        M = max(A)
        for i, a in enumerate(A):
            if M == a:
                if i != 0 and i != n-1:
                    if A[i-1] != M or A[i+1] != M:
                        print(i+1)
                        break
                elif i == 0:
                    if A[i+1] != M:
                        print(i+1)
                        break
                else:
                    if A[i-1] != M:
                        print(i+1)
                        break
