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())):
    n=int(input())
    arr=list(map(int,input().split()))
    if len(set(arr))==1:
        print(-1)
    else:
        maxi=max(arr)
        ind=[]
        for i in range(n):
            if arr[i]==maxi:
                ind.append(i+1)
        # print(ind)
        ans=ind[0]
        for i in range(1,len(ind)):
            # print("he")
            if ind[i]-ind[i-1]!=1:
                ans=ind[i]
                break
        else:
            if ind[-1]!=n:
                ans=ind[-1]

        print(ans)
