Have you checked what the alternator is doing ? Is the battery doing flat ?,and really I would check the plug on the back of the clocks.The car I mentioned previously was up for sale when this happened and a guy came to look at it and said the alternator was goosed and so were some of the electrics.The rev counter only worked if revved really hard,the fuel gauge worked intermittently,the battery light didn't work until you revved it and then it stayed on the front fogs didnt work and the tick over was all over the place,Its worth checking the plug imo and its free
It took me 5mins to fix.