Your best bet is to:
1. Consult your owner's manual: If you still have the original, it might have a diagram of the fuse box and relay locations.
2. Check the underhood fuse box: This is the most likely location. The fuse box will usually have a cover with a diagram showing the fuses and relays. Look for a relay that is labeled "power door locks," "door locks," or something similar. If you see several relays of similar size and you're not sure, carefully examine the diagram and any markings on the relays themselves for clues.
3. Check the interior fuse box: Some Camaros, particularly those with more features, might have a secondary fuse box inside the cabin, often under the dash. Check this as well.
4. Use a wiring diagram: A wiring diagram specific to your 1990 Camaro RS will definitively show the relay's location and circuit. You can find these online through forums dedicated to 3rd generation Camaros (like ThirdGen.org), or through automotive repair manual providers such as Haynes or Chilton.
Important Note: Before working on any electrical components, disconnect the negative battery terminal to prevent accidental shorts or damage.
