Hi, I finished my build in late 2016 and have been running my car when suitable venues have been available since then, maybe once every couple of months. Just recently a new car park has been built in advance of a new sports centre due to open next year. This is usually now empty and ideal as a running venue. In case this might happen to others, when I took the car out last week everything was fine until nearing the end, when I lost all control of the car and it started to career around the car park at some 15/20 miles an hour. Anticipating major damage to the car should it hit something, I tried to intercept it. My first attempt ended in a broken back wing with the car still going around. The second attempt resulted in a broken front wing but I managed to catch it. It was still revving fast and I had to put my finger over the exhaust pipe to kill the engine.
On checking the car when I got home, I found that the on/off switch had completely come apart inside the car, no doubt caused by the unavoidable running over stones/gravel found on any hard surface. I had been worried about the switch button protruding on the under side for some time but did not expect the whole switch to collapse. I had bought a spare some time ago but did not expect the car to go out of control when/if the switch broke.
It has taken me a over a week to repair the car and luckily I already had most spare parts which I puchased at the end of my build, when I could see the parts likely to get damaged in general use.
Finaly when fitting the new switch, I have put the plastic on/off cover plate inside the car under the switch in order to reduce the amount of the switch button protruding through to the underside. I have also made a metal cover plate to go on the underside as the plastic one on the original switch had just worn away on the underside.
Whereas there is a fail safe mode if the car goes out of range of the transmitter, I never expected to have the car go out of control, as happened to me in this case? Again I am just posting this for awareness to others.

Hi Andreas, thanks for your reply. I can assure you the switch was assembled correctly with on to the back of the car. I now understand why if the switch gets turned off, the engine keeps running. I assume therefore that when the switch collapsed the force of whatever it hit was enough to move the swich button to off or the connection broke when the switch assembly broke. I will obviously pay particular attention to the switch in future but believe the modifications I have done should minimise the likelyhood of it happening again. Again thanks.