I took my 110 Defender TD5 off road (for the first time) on some pretty muddy hilly sections. On a couple of muddy rutted up-hill sections I got in to trouble, lost traction and had to reverse and have another go. I tried with and with out diff lock which seemed to make no difference. When I select diff lock on, the warning light comes on if I hold the selector hard left. It goes off as soon as I loose it and stays off. So after all that rambling the question is, how do I actually know the diff lock is working?