I have changed the ECU, ignition switch, control assy and a control module which sits next to the control assy? I was going to change them back to original and do some voltage and continuity tests.
Yes. It would be best to put everything back as it was, and and just go stepwise through the basic electrical system. Look again at the first two responses to your original post.
It is an
intermittent problem. That means that simply putting a tester on a point to check for voltage, resistance, etc is probably not going to help -- since the problem may not be there at that moment. It could be that the issue is created by movement -- "exiting a roundabout" -- or something else.
One first test, after everything is back the way it was: turn the key to the ignition position, without starting the engine, so that the electrics are on. Then try wobbling things: the key, the lines from the battery, any major electrical item under the bonnet. You are looking for a wire or connection that makes the electrics react when you move it. If that test doesn't turn up a suspect, turn the car off again, remove the battery, and start the wiring check point by point.
Start from a certain point, the battery for example, and follow the connections. Examine every connection point, and every wire. Look for failed insulation, or corrosion, or broken connector housings, or loose connections. Remove the ground straps and make sure they are perfect. Wire-brush the ground points and reattach connections securely. That kind of thing.
At some point you may run down the battery with all this faffing about, but that's ok, may be time for a fresh one anyhow. Don't let it stop you.
Good luck.
