Recommended mechanic for electrical

[formulaC]

Hey guys, i guess this is also my introductory post, but i'm well aware of the search option. i'm having some trouble with the cluster on my 1989 s13 and wanted to know if there were any mechanics that might know how to deal with this specific problem.

a new HUD cluster that i purchased doesn't work which doesn't surprise me. at first, nothing came on at all except for the red status bulbs on the right, but after replacing some bad grounds i got everything to work EXCEPT for the digital speedo. i even ran the capacitor test and got no response, so i'm not sure what the problem could be. i read that a bad ECU might be the source, but i'm inexperienced in that field and need some professional help.

more specifically, i'm looking from someone who is very familiar with 240s or older nissans in general, since i know this is a very typical problem specific to ours cars. i'm located in southern california in the same city as Six Flags Magic Mountain, but am willing to drive out anywhere in the LA County to get this resolved. i'd tinker more but i simply don't have the time--thanks for any tips!