I would totally agree with Methyl – it is almost certainly an earth (or return) path fault.
The reason it happens when the blower or wipers are switched on is that these draw a high current and the voltage at the circuit location where these are ‘earthed’ (which should be 0V) rises enough to upset the ECU. They may even share the ECU return path.
If the control (switches) of the wiper and blower are in the + supply to both – then a simple fix might be to locate the 0V returns and splice in an extra earth connection to them.
Other than that, check all chassis electrical grounding/return connections for corrosion which may indicate a poor electrical connection.