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

/**
 * @Created_by : Lucent868
 * @Date : 13 Jul, 2021
 * @Time :  8:45 PM
 */

import java.util.*;
import java.io.*;
import java.math.*;

public class C {
    static InputReader in;
    static PrintWriter out;

    public static void main(String args[]) {
        new Thread(null, new Runnable() {
            public void run() {
                try {
                    solve();
                    out.flush();
                    out.close();
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        }, "1", 1 << 26).start();
    }

    public static void solve() {
        in = new InputReader(System.in);
        out = new PrintWriter(System.out);

        int t = in.nextInt();
        while (t-- > 0) {
          int n = in.nextInt();
          int a[] = in.nextIntArray(n);

          HashSet<Integer> hs = new HashSet<>();
            for (int i = 0; i < n; i++) {
                hs.add(a[i]);
            }
            if(hs.size() == 1)
            {
                out.println(-1);
            }
            else
            {
                int idx = 0;
                int max =  0;
                for (int i = 0; i < n; i++) {
                    if(a[i] > max)
                    {
                        max = a[i];
                        idx = i;
                    }
                }

                out.println(idx+1);
            }
        }
    }

    static class InputReader {
        private final InputStream stream;
        private final byte[] buf = new byte[8192];
        private int curChar, numChars;
        private SpaceCharFilter filter;

        public InputReader(InputStream stream) {
            this.stream = stream;
        }

        public int read() {
            if (numChars == -1) {
                throw new InputMismatchException();
            }
            if (curChar >= numChars) {
                curChar = 0;
                try {
                    numChars = stream.read(buf);
                } catch (IOException e) {
                    throw new InputMismatchException();
                }
                if (numChars <= 0) {
                    return -1;
                }
            }
            return buf[curChar++];
        }

        public String nextLine() {
            int c = read();
            while (isSpaceChar(c)) {
                c = read();
            }
            StringBuilder res = new StringBuilder();
            do {
                res.appendCodePoint(c);
                c = read();
            } while (!isEndOfLine(c));
            return res.toString();
        }

        public String readString() {
            int c = read();
            while (isSpaceChar(c)) {
                c = read();
            }
            StringBuilder res = new StringBuilder();
            do {
                res.appendCodePoint(c);
                c = read();
            } while (!isSpaceChar(c));
            return res.toString();
        }

        public long nextLong() {
            int c = read();
            while (isSpaceChar(c)) {
                c = read();
            }
            int sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = read();
            }
            long res = 0;
            do {
                if (c < '0' || c > '9') {
                    throw new InputMismatchException();
                }
                res *= 10;
                res += c - '0';
                c = read();
            } while (!isSpaceChar(c));
            return res * sgn;
        }

        public int nextInt() {
            int c = read();
            while (isSpaceChar(c)) {
                c = read();
            }
            int sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = read();
            }
            int res = 0;
            do {
                if (c < '0' || c > '9') {
                    throw new InputMismatchException();
                }
                res *= 10;
                res += c - '0';
                c = read();
            } while (!isSpaceChar(c));
            return res * sgn;
        }

        public int[] nextIntArray(int n) {
            int[] arr = new int[n];
            for (int i = 0; i < n; i++) {
                arr[i] = nextInt();
            }
            return arr;
        }

        public long[] nextLongArray(int n) {
            long[] arr = new long[n];
            for (int i = 0; i < n; i++) {
                arr[i] = nextLong();
            }
            return arr;
        }

        public boolean isSpaceChar(int c) {
            if (filter != null)
                return filter.isSpaceChar(c);
            return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
        }

        private boolean isEndOfLine(int c) {
            return c == '\n' || c == '\r' || c == -1;
        }

        public interface SpaceCharFilter {
            public boolean isSpaceChar(int ch);
        }
    }

    public static int[] sort(int[] arr) {
        List<Integer> temp = new ArrayList();
        for (int i : arr) temp.add(i);
        Collections.sort(temp);
        int start = 0;
        for (int i : temp) arr[start++] = i;
        return arr;
    }

    public static long[] sort(long[] arr) {
        List<Long> temp = new ArrayList();
        for (long i : arr) temp.add(i);
        Collections.sort(temp);
        int start = 0;
        for (long i : temp) arr[start++] = i;
        return arr;
    }

    public static int bs(int[] a, int fromIndex, int toIndex,
                         double key) {
        int low = fromIndex;
        int high = toIndex - 1;

        while (low <= high) {
            int mid = (low + high) >>> 1;
            long midVal = a[mid];

            if (midVal < key)
                low = mid + 1;
            else if (midVal > key)
                high = mid - 1;
            else
                return mid; // key found
        }
        return -(low + 1);  // key not found.
    }

}








