I have '88 e30 316, and a problem with my temperature gauge. When I
start my car it starts to go out of blue area, and then it starts to
jerk to left or right. Car was not driven for ~7 years, and as I
remember it used to sit vertically when engine is at normal running
temperature. Now it is about half way from blue to vertical, and
jerking from time to time.

I changed dash panel recently with a used one, and it still jerks.
Yesterday I changed temp sending unit - still jerks.

Perhaps there is some bad contact somewhere. I wanted to test it with
my old dash panel, but I can not figure out which wire to connect to
what. I have Haynes, Bentley and some German manual for e30 and none
helped.

I took dash panel apart and it seems that one connection goes to the
blue connector pin 26, and other two (ground and other connection of
the temp gauge) go to the board that controls green, yellow and red
service lights.

Can anyone tell me color code of the wire where to connect +12V, where
ground, and where temp sender?

Or perhaps this is some common fault and known solution?