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


import sys
from collections import defaultdict 
from sys import maxsize
def ini(): return int(sys.stdin.readline())
def inp(): return map(int, sys.stdin.readline().strip().split())
def li(): return list(map(int, sys.stdin.readline().strip().split()))
for _ in range(ini()):
    n=ini()
    l=li()
    if len(set(l))==1:
        print(-1)
    else:
        m=max(l)
        t=[]
        for i in range(n):
            if m==l[i]:
                t+=[i]
        for i in t:
            if i==0 and l[i+1]!=m:
                print(i+1)
                break
            if i==n-1 and l[i-1]!=m:
                print(i+1)
                break
            if i!=0 and i!=n-1 and (l[i+1]!=m or  l[i-1]!=m):
                print(i+1)
                break
