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I've got a (UK) 2005 Ford Focus C-Max zetec with electrical problems. It started with intermittent wipers, indicator lamps, central locking and interior lights either not working or coming on/sticking on even when switched off, and sometimes with the ignition off (which would drain the battery). All points to the GEM, but there is no sign of any corrosion or water ingress.

Now none of the functions controlled by the GEM work at all (instrument cluster and engine management are fine). I bought a second hand GEM (exact same model number) but it has made no difference.

I'm thinking must be an issue with the connectors to the GEM somewhere. The ends that plug into the GEM are all fine, but any advice as to where else I might try looking for corrosion or loose connections? It's not at all easy to trace where the cables go.

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  • Welcome to Motor Vehicle Maintenance & Repair!
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Mar 16, 2018 at 23:52
  • Did you check if your battery and alternator works ok? I mean, there is no under/overvoltage happening which causes GEM to malfunction? Second think to check is ground cable, maybe one of them is loose or corroded?
    – Mark
    Commented Mar 19, 2018 at 7:41
  • 14.4V across the battery with the engine at idle which seems ok? I'll have a look at the grounds (are there any others beside the obvious one to the right of the battery?)
    – aucuparia
    Commented Mar 19, 2018 at 21:22

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This turned out to be that one of the (many) wires going into one of the connectors had been crushed against the chassis - probably last time a fuse was changed. Over time with passengers kicking the footwell and bags being wedged under it, the wire had broken.

The Ford Focus 2004.75 (07.2004-) Workshop Manual (e.g. hosted at workshop-manuals.com) was helpful tracing this - it doesn't have full pinouts but it does for some critical ones (power, ground) and info on where to test them.

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