When asking questions its always best to quote the year and engine type.
Anyway what ever the year and engine,the favorite item on these old 306`s would be the heater blower rheostat,I`ve changed loads of them.
Its hidden. You will have to remove the wiper arms and the plastic grill that surrounds them. Then the plastic cover above the blower motor intake,and there it is. Multi plug off, twist it and out she comes.
I have a 1994 peugeot 306 xsi and have a weird problem with my gauges
When i turn up my interior fan speed, my coolant temp goes up and my fuel gauge
I guess its something electrical but i dont really know