rob, if your wanting to boost the earths on the cra then its a good effort to change over the ones from the negative terminal tpo the chassis, negative terminal to the gearbox and the gearbox to the battery clamp!!
i did mine a couple of weeks ago and was suprised at how cheap a good earth cable is!!

that cable only cost me £7 from my local electric deisel testing type place! ( the thin flat one in the pic cost me £3.50!!) the others for the earth terminal to the chassis and cogbox are only 2-3quid each too! then you'll have a very good earth up front!!!