Having a hard time with swapped in gauge cluster

Having a hard time with swapped in gauge cluster

Everything works except the tach. I'm trying to run a wire from the tach diagnostic port under the hood through the firewall and then to the cluster, since my 94 base model didn't come wired up for a tach from the factory. According to the haynes manual, the tach wire should be #5 on the blue plug that connects to the cluster. So, I connected a wire from the diagnostic port into that #5 slot, but the tach still isn't working.

Now, I'm thinking there must be a voltage difference or something that isn't allowing the tach to read the signal. Anyone know what the specs of the signal at diagnostic port are vs. the signal the 93-97 stock tach reads?

it might not be grounded. on some cars you also have to run a tach ground. on my old mirage i had to do that to hook up a tached cluster. not sure about the corolla though.