Intermittent loss of power (limp mode)

I am hoping to sort out an intermittent fault that’s been plaguing me since I returned my tf to the road in the spring. What’s so infuriating is that it doesn’t seem to follow any rhyme or reason. As I drive along you get a sudden drop in power and the dash light all come on and off and what I can only describe as similar to limp mode. When you get to the side of the road and allow it to cut out, sometimes turning the key gives no life at all, but the second turn fires up and carries on as if nothing is wrong. I know they do not have limp mode such a mode, but it mimics the same characteristics. I have had the crank and cam sensor changed but still it hasn’t cured it
I have linked Pscan and managed to bring up 3 codes (I do not have a/c or ASB fitted)
P0500 – Vehicle speed sensor malfunction
P1539 - Power to A/f clutch circuit over current
P0562 – System voltage low
Having had a chat with someone much better at car electrics than me, he suggested checking all the earth points.
He suggested that maybe an earth is playing up, bearing in mind I’ve had both subframes out and the problem only began since putting it all back together.
To date, I’ve cleaned the earth point from battery to wing, and the Earth point on the rear of the boot under 80A fuse. I appreciate there are several more to locate and clean, and this forum has a great listing of said earth points.
He also suggested attaching an additional earth from the engine to body work and see, in the short term, if that cures the problem.

Do you think this is a realistic avenue to follow?

I’d moved the battery from an out of sorts f into the ever eager tf & experience problems similar to this. For some reason I had failed to nip the positive terminal, swift wrist action with a 13mm spanner resolved the problem.
If you look in the “community “ pages & IIRC there’s a list of earth points in one of the technical documents.

Yes, I found the earth points on the forum post, and I have checked the battery terminals, but thanks for your help. I have a disconnect fitted, might try with it removed to see if that helps at all.

You can never have too many earthing points…. My standard solution to hard to access earthing points is spice in another somewhere that offers easier access

As I said on the other forum, use pscan to full effect and get a data log of live data from all the sensors. Also, clear the faults using pscan as they could well be historic - see what comes back.

I would also check the alternator output and the integrity of the connection from alternator to battery.