Muddymike :
I have recently changed my car. The new one has a fancy socket in the
glove box that charges and transfers information from my iPhone. I
bought a lead to extend this socket up to a dash mounted phone holder
so that I can see the screen when using the Tom Tom app.

One lead was not long enough so I bought a second and had it
professionally installed behind the dash. Not DIY I know but I didn't
feel confident enough to start pulling the dashboard of a new car apart
to route the cable myself.

When plugged directly into the socket the phone takes a charge. When
connected via the leads the charge symbol shows on the phone screen but
it does not actually charge.

I have queried this with the cable manufacturers who claim it is
probably because two cables linked together is too long a run. They
will happily refund the cost of the cables but won't contribute towards
having them professionally replaced.

Any thoughts on the long run issue

This is an ongoing issue with me, in a two-iphones-two-ipads-two-ipods
household with multiple charging locations. Some cables look as if they
are charging, but don't. I don't think length is the only issue because
I've found third-party leads that are the same length as the official
Apple leads, but don't work properly. I think the thickness of the
conductors might have something to do with it. Much as it pains me to
say so, IME the only way to get something that really works is to get an
official Apple lead.

or whether they are liable for my installation costs appreciated.

If you can show that an Apple lead of the same length works any
better[1], then you have a very slim chance. Otherwise, none.


[1] You don't need to install it behind the dash.

--
Mike Barnes