oil switch ?

[crackfox1]

Hello, I recently purchased a 1980 monza with an oil light permanently on and disaffected amp, clock and fuel gauge. I've read that the problem is more than likely the oil pressure switch. What strikes me as odd is the switch has only one terminal but there are two wires. The switch has a tapered 16mm thread which is larger than the ones I've found online. The engine is a 2.5L four cylinder type. Any help on this issue would be welcomed. Thank you. Simon.

[Monza Harry]

Simon that thread would more than likely be a "Pipe Thread" I can't think of an engine with a 3/8NPT thread (tap drill for 3/8NPT is 9/16" and the plug/fitting would be about 5/8" fat which is approx. 16mm) I don't remember what size the Inline 4 has but the V8 is 1/8NPT and the 3.8L is 1/4NPT) I know that you use a different pipe thread than the North American standard of NPT you use BSPT. I don't know if they can be interchanged or not. I would think you will have to order these from the US or Canada. The taper should be 3/4"/ft. and the outside diameter for the 1/8 (tap drill is "Q" and is approx. 8.25mm) will be near 10mm dia. the 1/4 will be near about 14mm dia. the tap drill is 7/16" and is 11.1mm. As for the wiring I don't have any experience with the 4 cyl. but I am sure someone will help out. Harry

I forgot to add these links for your reading pleasure! BSP(T) http://en.wikipedia.org/wiki/British_Standard_Pipe and NPT http://en.wikipedia.org/wiki/National_pipe_thread

[spencerforhire]

A couple of notes- the H-body oil pressure switch usually has 3 wires, but on a 4cyl Monza 2.5 I see only 2 on the diagram; orange(accessory) and blue w. white(fuel pump). If by "disaffected" you mean not working, the clock and fuel gauge are on 2 separate circuits fed from different fuses. You also mention "amp"; are we talking about a light or a gauge?.
As to the large thread on the sender, that sounds more like the one for coolant temp, not an oil pressure sender.

[crackfox1]

Thanks for the info Spencer, your quite right, the switch I've pulled is the coolant switch. Now that I feel like a dummy I may as well ask where is the oil pressure switch located ? Thank you. Simon.

[classic_cruiser]

If this is a late 2.5L, the oil switch is underneath the intake manifold on the right side of the engine, to the front of the distributor.