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


def ans(ar,n):
    k = max(ar)
    b = []
    for i in range(len(ar)):
        if ar[i] == k:
            b.append(i)
    for i in range(len(b)-1):
        if b[i]+1!=b[i+1]:
            return i+1
    return b[-1]+1

for _ in range(int(input())):
    n = int(input())
    ar = [int(i) for i in input().split()]
    if min(ar)==max(ar):
        print(-1)
    else:
        # left = (n-1)//2
        # right = left
        # maxx = -1
        # maxPtr = left
        # while left>-1 or right<n:
        #     if ar[left] > maxx:
        #         maxx = ar[left]
        #         maxPtr = left
        #     if ar[right] > maxx:
        #         maxx = ar[right]
        #         maxPtr = right
        #         print(right,maxPtr)
        #     left-=1
        #     right+=1
        # print(maxPtr+1)
        print(ans(ar,n))
        
