If you install a aftermarket oil pressure gauge (electric type / not mech) you will need to install a new sender unit. The gauge and sender are married, and the stock sender will not work with your aftermarket gauge. If you gauge did not come with a sender then you need to find the correct one that goes with your gauge.
Most senders are 1/8 inch NPT thread. Our cars need Metric Thread. you can buy the adaptor online (3sx charges 17 bucks!) i found mine for 5 bucks at a local shop called 'Central Hydrolics' none of my local autopart stores had them but lucky for me a local auto parts store employee knew what store did have it.
You will most likely also need a 'elbow' as most sender units are 'bigger then a freaking sweet potato'
You do not need to drain your oil to remove and install a new sender, or to just remove yours for cleaning. Oil will come out, about 1/4 of a cup (kitchen measurement) so keep a paper cup handy to catch the mess.
Here is a pic of my dirty one. i pulled it off and cleaned it and it works alot better now.
If anyone would like to add this info the wiki feel free....im wikiliterate
