Audi 80 b4 - the oil indicator is on and the tachometer does not work sometimes

Hello.
Audi 80 B4 un4 counter, minicheck VDO.
After turning on the engine, the oil indicator light is on, sometimes it goes out for a moment, but rarely, sometimes the tachometer stops working while driving.
After connecting another meter, everything was OK. So I found info that maybe the problem is cold February:
audi80.pl/topics77/80-b4-abk-kontrolka-oleju-i-obrotomierz-vt22113.htm#276654
so I corrected all February on the boards, i.e. I heated the contacts one by one with a soldering iron and if necessary, I added some tin and all the contacts except for a small chip on the minicheck. After assembling, the counter worked properly for 2 days .. and now the problem is the same as before
Did I correct these contacts well or should I do it differently?
Do you know which contacts are responsible for this problem so as not to make all the contacts again?




minicheck:

Bad soldering quality. Some component leads are not soldered at all. You have to give some electronics to improve February and it will be OK.

jano932 wrote:

Did I correct these contacts well or should I do it differently?

It is bad, because the old tin is removed with a suction machine and only the new, better because with lead, is applied.

After tweaking the solders again, they all sparkle (they are empty in some places where there are no leads), the tin was sucked off and then soldered with tin and lead and everything worked for about 3 weeks and the problem returned again. First, the oil light came on, and after a few days the tachometer. While driving, it sometimes goes off and the tachometer sometimes stops working. I am not sure if the problem is due to cold February or how it is removed and then disassembled, it displays then, for example, on the plugs it starts to connect and works. The protruding pins from the minicheck and plugs were immediately so strangely dark as if overheated, I cleaned them with fine sandpaper. I am still wondering whether I should spray the plugs with the "contact u" preparation. Do I need to turn off the battery? Is it safe for such plugins?