Defender Td5 electrical questions

Hi guys,
I have a 2003 defender td5 and I have some questions about some of the electrics.
My first question is about my temperature gauge. When I use the accelerator pedal, the temperature will drop from the normal to almost zero. It will also fluctuate when the handbrake is being put up or down. I have read that a new ecu earth to the battery negative could sort this and I have some 2.5mm^2 wire I could use. Would this wire be suitable for this use or do I need something a bit thicker?
The second thing I'd like to ask is about some electrical connectors ive found around the car which aren't plugged in. I'll attach some pictures of the connectors I've found so far. I'd like it if anyone would be able to tell me what they could be for.
The first connector is in the ecu box under the seat. The second and third are behind the radio, and the fourth and fifth are in the engine bay near the brake servo.

Odd electrical occurrences are usually a bad earth. The fact that it changes when you put the handbrake on reinforces this. Try putting an extra earth from the gearbox to the chassis, use a proper earth strap, at the moment its trying to earth though the handbrake cable. Test using a jump lead first. Check clean and tighten all other earth as well, cover with Vaseline when done.

I'm no expert. But have a look at the battery earth cable, follow it until it meets the chassis, and clean the connection to chassis. Then it should then loop onto the back of the transfer box. Clean both connections well back to clean metal.
I also have an earth strap from bulkhead to chassis rail on drivers side.

As for connectors. Is this any use?
https://www.lrworkshop.com/connectors/defender-2002my

There is a manual for connectors, and electrical wiring diagrams for defender td5. Google search usually finds them.

Hope this helps

As wireman stated there is a special contact grease that is recommended by land rover which gives protection
LR054614

Thanks guys for the responses. I've been and cleaned the chassis, transfer box and bulkhead earths but unfortunately to no avail. Based on this I'm guessing my next step is to add a new earth somewhere. Are there any places that anyone could recommend I add one, or is it more of a matter of trial and error until the problem is sorted?

Get a strap similar to this:
https://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=p2047675.m570.l1313&_nkw=121930638013&_sacat=0

Then attach it to the transfer box/gearbox near to the handbrake, then attach it to the chassis, try using one of the bolts that holds the gearbox cross member on. Remember the connections have to be clean and tight.

Okay so I've just fitted a new earth strap from the gearbox crossmember to the transfer box, where there are already 2 small earths. The temperature gauge appears to drop less than it used to when I apply the throttle, but it is still dropping a fair amount and is still fluctuating with the handbrake. Has anyone got any suggestions on what steps I should take next?

I had exactly this and cleaned all earth points up. Stopped once I’d done this. I also installed an earth from ecu earth post to battery neg

wireman said:

Odd electrical occurrences are usually a bad earth. The fact that it changes when you put the handbrake on reinforces this. Try putting an extra earth from the gearbox to the chassis, use a proper earth strap, at the moment its trying to earth though the handbrake cable. Test using a jump lead first. Check clean and tighten all other earth as well, cover with Vaseline when done.

Click to expand...

As I always say, you can never have too many earths on a Landy ... dunt matter what one it is ...

Hi guys, just thought I'd update this thread, it's been a while. I have now fixed the temperature gauge issues. I did this by running a new earth from the ECU to the battery negative. As for those connectors, that link that was posted earlier was very useful and informative and I have identified most of them.
Thanks

Thanks for letting everyone know, it helps when people are searching for a similar problem ...