my computer fried so I am trying to hard wire the Speedo. I saw on here that all you have to do is ground the blue wire on the vss now when I drive the needle goes all over the place and won’t stay still any suggestions? I was thinking not a good enough ground I have a 91.5 w250

 

Anyone got any ideas?that’s for me

 

I already replaced the vss

 

'91.5 is a special 1/2 year wire harness and PCM.
Just an FYI as the wiring is different than the '92/'93 trucks that also have a PCM