A nipple is just a threaded piece of brass tubing.
I swapped mine to that extra plug you hear about since that first post. The reason I removed my stock sender was because I stripped the extra plug trying to get it out, but I borrowed some easy-outs from a friend and got that extra plug out. You have a '98 so I don't think you have that extra plug in the oil filter housing. If you do:
You go to ace hardware or home depot, and buy a brass elbow with 1/4" NPT female ends (they call it a 1/4" Ell,) a 1/4" NPT nipple, and some teflon tape.
Wrap the threads of the nipple with teflon tape, and screw it in to the elbow. Then remove that plug and screw in the elbow in to the hole with your fingers, then use vice grips to tighten it some more. Next, wrap the threads of the adapter which comes with the gauge with teflon tape, and install it in to the other hole of the elbow, and tighten it. Then, wrap the threads of the sender included with the guage with teflon tape, and install it in to the elbow.
If you don't have the plug (which I don't think you will,) you'll need to go to home depot, and buy Watts PN A-740 & A-738. It's basically a t-fitting and the nipple. You'll need to remove your stock sending unit, and re-wrap the threads with teflon tape. Wrap the threads of the nipple with teflon tape, and install it in to one side of the t-fitting. Now, screw that in to the hole your stock sender was in. Then, install your stock sender in to one hole of the t-fitting, wrap the threads of the adapter that came with the gauge with teflon tape, and install it in to the other hole of the t-fitting, wrap the threads of the sender which came with the gauge with teflon tape, and install it. Tighten it all down and wire it up and you're g2g.
