ECU earth sheared off

Hi all, apologies if this has been answered elsewhere - I couldn’t find anything specific - I’ve been having an issue starting my Defender Td5 for a while, and it’s been impossible to start in the cold weather. I bought a new battery and thought I’d clean a few earths up before trying again, but the first one I came to (beside the ECU), the bolt sheared off as I touched it. Thinking this may have been a big contributor to my woes, but how can I reattach the earth? Should I drill the hole through?
Thanks, Kelvin

Is there another handy earth point nearby? on my TD5 there's a stud with a nut on it on that shelf that the fusebox sits on.

If needs must there's no harm in drilling a hole and putting a bolt in, but it's also worth cleaning the paint off so there's good contact between the bold head and the metalwork.

It also helps if you fit another earth wire from the box under the driver's seat to the negative battery terminal.

Are your glowplugs working? The yellow glowplug light on the dash is supplied by the ECU and doesn't necessarily mean they are heating up, so it might be worth a little investigation.

Thanks for the quick response, Brown. Yes I can use that fuse box shelf - I wasn’t sure if the original location was of some importance - but I’ll give the shelf a try.
The glow plugs seem to be ok - I’ve had a mysterious issue for a while whereby it turns over when starting but won’t fire - remove the seat and take the glow plug relay out, pop back in and fire up. Replaced with new relay but no change. I’m hoping this barley-attached ground is the issue

Hello again… so the lug connector has completely corroded to the sheared off bolt - I’m going to have to cut the wire. I just wanted to check I’d be safe adding a short length of 17 AWG so it reaches the shelf?
Thanks

No problem. Solder the extension wire to the existing and cover with heatshrink or a self-amalg' tape.
The bolt that snapped .... whats on the other side ?

I’ve just had a look and it seems like it’s not a bolt but a screw, but won’t budge.
Apologies - I meant 17Amp cable in my last message - I guess this is ok to use (as well as using this for the return cable to the battery -)?

You may be able to simply drill that out (or twist it out with a pair of mole grips) the steel will be relatively soft, or just ignore it and drill a new hole next to it .....
I find these drill/taps extremly usefull ... https://www.ebay.co.uk/itm/284540125383

Clean off any paint etc to epose clean meta, fit an M6 brass bolt ...



I have these all over my landy, they are really handy.
Once fitted I paint over the underside and slather on grease.

Quick update, followed your advice and fired up first time thanks for your help