Stock 4k tach problems

[travis401]

So I bought a cluster off someone on here with the 4k diesel tach with integrated fuel gauge. Got everything hooked up and the tach doesn't work right. It zeros out when I turn the ignition to on, but when I start the truck, the tach only reads about 150-200 rpm and when I rev it, the needle does move up, but just barely. I know there's a post on here to fix non working 5k tachs by cutting a couple of traces on the circuit board and soldering in a resistor, but the 4k diesel tach is a different board and the traces to cut, aren't there. Ive already tested the signal coming from the distributor with my Autometer tach and it reads fine, so I know the problem is in the tach itself.