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(int(input())):
	index=1
	inde=1
	n=int(input())
	l=list(map(int,input().split()))
	ma=max(l)
	p=l.count(ma)
	i=0
	u=len(l)
	for i in range(n-1):
		if l[i]==ma and l[i+1]!=ma:
			index=i
		elif l[i]==ma and l[i-1]!=ma:
			index=i
	for i in range(n):
		if l[i]==ma:
			inde=i
			# print(l[i])
	a=len(set(l))
	if a>=2:
		if index>=0 and p>1:
			print(index+1)
		elif p==1:
			print(inde+1)
	else:
		print(-1)