tachomter problem ... help needed!

[the E30project]

i recently installed a gauge cluster using a custom piece in my center stack. the set included a oil pressure gauge, a water temp gague and an ammeter. all the installs went fine, but now my tachometer will not work. at all. all the other stock gauges seem to be working fine (fuel, temp, speedo) ... so it seems as though the tach was all the was affected. the real time fuel usage gauge (mileage) is also not working, but i suspect that it uses a feed from the tach to figure out mileage.

so my question is this: what would cause that? none of the wiring i ran went under the dash on the driver's side, so i don't think i messed with a ground or anything. i checked all my fuses and they seem to be fine. i even replaced the one for the tach just to be sure. does anyone know where the tach pulls its signal from? maybe i disrupted something under the hood when i ran the line for the ammeter. i can't imagine i fried the tach since the fuse was good. also, it appears as though my SI board is still working.

i tried consulting both the haynes manual and the bentley, but i can't seem to find any information. if someone can shed some light on the subject, please do. i have an extra cluster in case i fried the actual gauge, but i suspect that the problem is something else. please help!

[the E30project]

no love for the newbies? no one knows where the sender for the tach is?

[ProjectE30]

My 86 325es rpm sensor AKA speed sensor is located by the starter, it's the one that hooks up to the black connector. 980ohms is what my DMM reads, 960ohms plus/minus 96 is normal. This should apply to 84-87 325e and es car, not sure about other models.

[the E30project]

right on, that's what i suspected. especially since that's the general area i was in hooking up the ammeter. i'll look into it.