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())
    l=list(map(int,input().split()))
    if len(set(l))==1:
        print(-1)
    else:
        d=max(l)
        for i in range(n):
            if l[i]==d:
                if i==0:
                    if l[i+1]==d:
                        pass
                    else:
                        print(i+1)
                        break
                elif i==n-1:
                    if l[i-1]==d:
                        pass
                    else:
                        print(i+1)
                        break
                else:
                    if l[i-1]!=d or l[i+1]!=d:
                        print(i+1)
                        break
                    else:
                        pass
