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 i in range(t):
    n=int(input())
    b=list(map(int,input().split()))
    if len(set(b))==1:
        print(-1)
    else:
        m=max(b)
        j=0
        while(j<n):
            if j<(n-1) and b[j]==m and b[j+1]!=m:
                print(j+1)
                break
            if j>0 and b[j]==m and b[j-1]!=m:
                print(j+1)
                break
            j+=1










