where do i start? massive chain reaction

ive just got the car on the road after a month of waiting (shes my daily so quite desperate).
the problem was sumit to do with the fuse box not energising the fuel pump.
so i know the garage has been messing around down there.
problem is they have been lurking in the engine bay aswell and im guessing alot of my problems are earth related.
any ideas???????

(1) ive got a wworking  rev counter  with the headlights off, then when i put the lights on the rev counter stops working.

(2) the full beam warning light is on during dip beam and goes off when full beam is on.

(3)the dash lights only light up when the engine is off and the headlights on. as soon as the engines started the dash lights dont work with the head lights.
  
(4) the trip computer is all screwed. apparently my oil temp is 320oC  lol

(5) the water temp gauge flashes when the lights are head lights are turned off (like its meant to when the ignition is switched to

any body?

it's gotta be an earth problem

have a look at the earth at the bottome of the steering colum, this earth is the one for alot of dash items

hth

as jelly says, check earths - bottom of steering colum, the big cluster of earths above the fuse box and the one going to the corner of the rocker cover.  Also clean and check the earth strap from body to gearbox and battery.

I recently changed my earth between chassis and gearbox as it fell apart. Also check the main feed from the battery to fuse box as ive had a volt drop due to corrosion. Could always get some new terminals and chop the wiring back a little. For how long it takes its not hard

Could be the ignition barrel switch......narrowed my fault down to that :0) .