temp & oil gauge not working

1....Go drum up a wiring diagram and closest you can get to a factory service manual over at MyMopar. You may have to settle for a Dart EG. This will be somewhat DIFFERENT than your ralley dash

2....Are the aftermarket gauges electric and did someone tap into the factory sender wires? Your clue is to look in the bay at the engine senders. If the factory wires are hooked to the oil/ temp sender, then they have been cut under the dash

(I don't know where you are connecting your test lamp?) "The wire??"

3...On a ralley dash, the three gauges, oil/ temp/ fuel all have the save voltage source from a regulating device IN the fuel gauge, so it is evident that it is working. That power comes OUT of the fuel gauge on a third stud on the rear of the cluster and jumpers over to the other two gauges by means of the PC board traces. It might be a simple as the trace being broken/ burnt, OR THE NUT on the gauge stud has become corroded

4...There are test resistors by which you can test the gauges, and there are hundreds of posts on this board about them

A search

67dart273, gauge tester - Google Search

An example

Help with Temp, Gas, Oil Alt gauges FREE VIDEO INCLUDED!

5...Also PLEASE READ this thread on PC board repair, as it gives you insight into "whut" 'kin go wrong:

Printed circuit pins repair