Earthing points in Engine Bay

Took car out a run today, first time for weeks. Ran ok after a jump start, went for 10 miles had to stop for petrol and jump started again. Was running really bad after this with a dead regular "cut" every 5 to 7 secs for about 2 secs. At first thought dirty fuel but far too regular and car will sit and tick over no problem for ages.

Thought it might be coil packs or connectors but when it happens everything is going dead, no warning lights, no odometer, absolutely nothing.

So I now think it is an earth (maybe not tightened properly after re-spray) Battery terminals checked and tight But I can't find any earthing points. Did a search and the only thing I came up with is that there are two in the passenger footwell. Can't see them. I am sure there must be one or two in the engine bay - can anyone point me in the right direction please?

Been out a short run and no longer think this is an earth problem, it is too regular, happensmaybe a dozen times, then car runs normal fo 30/60 secs then it starts happening again, no matter what gear, what revs. Can't seem to get an error code but that is nothing to go on because I have never had any success reading them

When this happens, does the rpm needle drop directly to zero, or does it still display the correct rpm? Do all of the dash lights go dead (especially the warning ones)?

Every thing goes dead Homer, rev counter goes to zero, everything including odometer off, totally electrically dead. Yet sits and idles and revs perfect when no load on it

There are two points where the loom is earthed on the intake manifold, one front one rear. There is also an earth lead from the rear engine hook to the bulkhead.

Thanks, need to some more investigating now

Got this fixed at weekernd, there was a loose plates(s) in the battery, jumping about anywhere between 12.4V and 0V depending on how you tilted the battery. Never discovered this until battery removed from car as it was giving a reasonable reading whilst sitting static