To whoever was thinking of running 2 wires from the stock sending unit....
The stock 'sending unit' is an on/off 12V trigger. If there is less than something like 7.5psi, it turns on the oil light in the dash. It does not have the capability to send fluctuating readings.
I don't understand why anyone would put a Tee in this location. It's such a pain to get to in the first place... it's difficult to do one connection much less 3!... VDO (and I would think autometer) makes a 0-80 psi sending unit with a low level warning contact. Affix the stock wire to the warning contact and the signal wire contact to the gauge. That's it.
I had the threads on the sending unit recut by the place I buy this stuff from,
www.nhspeedometer.com. They're fairly easy to work with. If you have a die-cut set, you can do it yourself. The adapter works, too.
I use RTV sensor-safe silicon on the threads despite what anyone else says about tapered threads. (which is what sending units generally have) I've replaced enough senders to know it works better than not. Also, if it's your first time doing this kind of thing, having to deal with a leak and trying to tighten this thing in its location is a real b****. This makes the oil filter look super easy to get to and deal with... which I think it is but, that's me.
Good luck for anyone doing this. You'll most likely need to remove the arm that supports the intake to the block to get it done. Give yourself some time for this one.