Aftermarket tachometer doesn't work when installed

Hello all,
I bought a aliexpress tachometer for my charade because it was cheap and i thought why not.
before i installed it i tested it by hooking it up directly and it worked. after i had installed it it stopped working. checked all the wires and they were all connected correctly. so i removed it and tried it directly again and it worked. neither me or my boss could figure out why and he’s been a mechanic for 40+ years
if anyone knows what my issue could be, please do let me know
thanks in advance.

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In which wire did you hook the signal cable on?

one of the wires that goes to the ignion coil. i checked it with a light and it flashed faster with more rpm and when i check it at the gauge it still flashes.

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picture of the gauge?

I dont have a picture but this is the link for it

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somewhere there is a broken wire