Hi all, hoping somebody may be able to help regarding an issue with my son's Fiesta.

Last week son was out driving and he suddenly lost power to headlights, radio and heater (not fully – lights dimming then coming back on type thing). At same time battery warning light and possibly other warning lights (he’s not sure) came on. Engine kept running ok but once home it wouldn’t start again but started with a jump start with booster cables. Took battery out and charged it. When battery back in everything seemed fine – started first time and no warning lights. Took for a drive for same thing to happen again – although this time the ABS warning light came on as well as battery light. Happened after he had braked sharply. Again wouldn’t start again after getting home. This has happened right when he was hoping to trade in/sell the Fiesta (£500-800 at best) so not sure if worth major expense. Is it worth trying a new battery or could it be something else in ignition/electrics?

Any help appreciated.

Worth checking battery leads and earth points.  

If that all checks out I'd suggest the alternator at fault.  Unlikely to be the battery as everything worked once it was charged properly.

A rough alternator check:     engine running on tickover/idle.  Switch everything on - all lights, heated rear window, quickclear windscreen if you have one, heater fan.  now rev engine slightly, do the lights go brighter than on idle? if so, you know the alternator is at least doing something.  

On my brother's Focus 1.8tdci we thought the alternator had failed but it turned out to be the one way clutch built into the pulley on the alternator that had worn out and the alternator itself was not being turned properly.  I do not know if any fiestas have than one way clutch alternator pulley. We don't know what year / engine fiesta this is. My brother bought a new (2nd hand) alternator. We only found it was in fact the pulley when we came to change the alternator. 

Have charged battery again and refitted. Car won't start at all now. Battery leads look OK but I'm a complete car novice so don't know where the earth points are.

Used this hack and it shows battery voltage as 12.2 so presumably battery charge is OK?

https://m.youtube.com/watch?v=bMtJW9nKJp4

Any other help appreciated.

Edited February 3, 20197 yr by souldriver
Missing info