You will have no problem fitting a TCS decoder into the 141/181 with or with out a harness. I've just fitted an 8 pin sound decoder/8 to 21 pin converter and a bass reflex speaker for a site member a very tight squeeze and some modifications were needed to the body and chassis but its all in there. All my own 141/181's use a 8 - 21 converters and decoders with harnesses I don't use the Bachmann decoders as they don't support CV 19 so no good for double heading unless you give both locos the same address.