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

for _ in range(input()):
    n = input()
    l = map(int, raw_input().split())
    if len(set(l)) == 1:
        print -1
    else:
        mx = max(l)
        # print mx
        for i in range(n):
            if l[i] == mx:
                if i == 0 and l[i + 1] != mx:
                    # print "ok"
                    print i + 1
                    break
                elif i == n - 1 and l[i - 1] != mx:
                    # print "ok2"
                    print i + 1
                    break
                elif 1 <= i < n - 1 and l[i - 1] != mx or l[i + 1] != mx:
                    # print "ok3"
                    print i + 1
                    break
