Originally Posted by
Paul Woods
Just in case your aftermarket temp gauge is telling you lies, you can get the stock Mk3 dash working by simply putting the Mk3 EFI sensor into the cooling system, run one of its wires to earth(brown wire) and the other to the Y/R wire on pin C14 on the Mk3 ECU, that's the third plug down. The ECU will then send the correct signal to the dash, it will also get your cooling fans working properly. Just make sure the old Mk3 ECU still has its power feeds,ignition feeds and earths.
This is how all V6 Mk3 swaps are wired.