Where is the usual location for these boxes? It is not at the speed sensor end so woild i be right in thinking its going to be behind the clocks somewhere?.
Can these converters cause problems which can look like a speed sensor failure? the reason i ask is i have the usuall symptoms of a faulty vss but it only does it for about 5 mins every day where the needle goes crazy or just dies, sometimes CEL which does give the code for vss fault.
Also the speed reading is out by alot 70mph reading on the clock is reading almost 100 on the sat nav.

Thanks