I've been having electrical issues which I have failed to resolve by throwing parts at it

Beginning of the year I was starting to get very occasional ABS/Hand Brake light warnings along with immobiliser bleeps whilst driving. Didn't seem to be any issue with how the car drove so put it down to old battery which I kept running down and then recharging due to lack of use. Then one day after a long run I stopped at a supermarket for 10 mins. On my return I unlock the car with the key remote and put the keys in the ignition. Nothing. Battery basically disconnected. No sign of life at all. Took the key out, tried again along with pressing the remote button etc. Battery back on line and car started. Pulled off but almost immediately the ABS/Hand Brake light came on along with the immobiliser/alarm bleeping away as if it was arming/disarming. This would continue for 30 seconds or so, then disappear for a few minutes only to return again. And then disappear. For 30mins through rush hour traffic. At no point did the engine appear to be effected, everything mechanical ran as normal.

So when I got back I chucked the old battery and fitted a brand new Yuasa one. Problem solved for a few months and hundreds of miles. Yesterday I fitted new belts as the PAS was squeaking at cold start and was visibly loose. All done and PAS now silent.Except my electrical gremlin has returned. Same as before, ABS/Hand Brake light on, immobiliser chirping. Drove a few miles to a garage to get some milk. Locked the car with the key button. Unlocked with the button on my return, put the key in the ignition - no battery. Took the key out, put it back in, battery back and car starts. Clock and odometer both reset, so battery definitely disconnected.

So where to start? Not battery. Not alternator (have checked charge). I don't think it's anything mechanical like earth as it would be doing it all the time and certainly not whilst the car is parked. Can the immobiliser actually disconnect the battery - I thought it was just ignition and fuel? Where else should I look? I mean it could be an ABS issue that is triggering the ABS/Hand Brake light - but why would that trigger the battery/immobiliser? Seems it's more likely that an irregular voltage is causing the ABS light to trigger.

 

sounds exactly like a potential Earth issue......either that or you have some wiring loom issue

 

I agree that an Earth seems the most likely cause of battery disconnect - but it seems odd that it's so varied and intermittent. Will do some logging and see if I can identify anything amiss.

 

It could be short circuit, had an issue when driving one of my cable connector from + terminal was touching intercooler pipe than instantly loosing electrical power with engine cut off and back to life second later.

 

+1 for earth problem. Check both ends at engine, battery, body. In fact anywhere there's an earth point.

 

The battery to wing earth was pretty corroded so cleaned it all up and no further issues so far. All the earth leads and grounding points look pretty tired so will replace them all with 4awg welding cable and new fittings in due course.