Remarkably reliable, it’s fair to say you’ll experience very few electrical problems with any Mk7 Fiesta.
The most likely niggles will be the boot release button, which tends to fail when moisture creeps into the microswitch, resulting in refusal to close or continual opening when driving along. Fortunately, replacement is cheap and simple.
The steering wheel audio controls and display have been known to fail, so make sure they’re working. DAB radios and the SYNC system are also prone to misbehaving, so check them before buying; the cure may be a simple software update or fuse-out reboot, or possibly a whole new stereo unit. Sometimes, fixes are even found by reading the manual…
If there’s sat nav fitted, ensure it works, and scroll through any menus to test functions fitted to higher models, such as rain-sensitive wipers. Various option packs offered keyless entry, starter button, Powerfold mirrors, heated seats, parking sensors, cruise control and climate control, so check they’re present and correct.
Make sure the dashboard lights aren’t giving any warnings – notably airbag and seatbelt lamps – and test the windscreen washers; sometimes a trapped hose can cause them to cease working. It’s worth testing the window switches, heater control and even the speakers, but don’t generally expect to discover anything amiss.
If your car has daytime running lights, check they work properly, rather than going dim when the indicators are operated – which happens when the units are failing.