Hi,
   While I had the fuel tank off, I noticed the electrical wires, particularly the Brown wire, 
has several cracks in the outer sheath exposing the wire when flexed.
   If I was to replace it, Is automotive electrical wiring suitable for ‘in tank’ application ?

      Cheers   Dale

No problem with that, but tinned marine wire is even better. 

Bill

I'm using PTFE insulated silvered wire in 16GA, like this:

http://www.ebay.ca/itm/16-AWG-Silver-PTFE-teflon-R-Wire-Assortment-25-feet-19-strand-/232495706826?hash=item3621d2f2ca

we use that stuff in our power supplies rob ...very good for thermal properties and tight spaces
but not sure if its petrol resistant
but certainly better than many of the "standard" pvc types of insulation ...em in a long term situation
i guess we have to be thankful  that not a lot of movement occurs after the wiring is installed ...till we need to change the fuel filters - pump

I researched gasoline-resistant insulation when I was selecting the product. Some people recommended PVC and others PTFE (Teflon). Teflon insulation has many desirable electrical and mechanical properties, and specifically superior resistance to chemicals when compared to PVC. I believe that this wire product should have a longer service life immersed in gasoline as compared to PVC coated wire; I will probably not live long enough to find out empirically so I'll just hedge my bets and use it.