hella hazard switch

fuses F22,F9 on BECM but if righthand is working unlikely and as Datatek said

relays

what make is the used tacho you are using

Are you referring to the starter relay or the anti-theft relay

try checking header connection on H289- 3 you may have disturbed it when chopping wiring

glad you fixed it :) you have to compensate for the lead resistance when on ohms scale and really you cant beat an old Avo mark 8 analogue meter that calibrated in my opinion and of course remove any voltage source

what year is it as the harness changes from 2000 to 2003

does the charge warning light work, main harness to engine harness connection ok .if the charge bulbs faulty no excitation same with bad harness connection unless it has a resistor and diode fitted to the loom ,looks like the voltages you are reading are the battery if all above ok then...

have a gander https://www.landyzone.co.uk/land-rover/rev-counter-for-4-cylinder-petrol.386612/ not sure I covered diesel

not strictly defender (P38) but land rover use same items on various models

don't try to short cut the bonding process , had a rear roof spoiler fitted by dealer for my son's birthday two week later it split and one piece left the car at motorway speeds never to be seen again

in my blind spot ,looks like they are made of gold judging by the greedy price's

check coolant connector for clean contacts

which switch ,and the relay in your pict is wiper relay. any images of switch in question and image of the headlight connections

what year ,does it have the dim/dip relay and has that been linked out by the PO

may help

first search https://www.partsgateway.co.uk/parts/detail/td5-r380-gearbox-tunnel-land-rover-defender-90-gear-lever-housing-cover/41490856

check the header's for corrosion whilst the dash is off they are a two part male and female connector

Dale Radford of Radford bulkheads has done some nice engine replacements in the series one club back in 2011 but you would have to become a member to excess them .pictures belong to dale attached