Headlight relay location 1998 dodge ram pickup

SOURCE: 96 Dodge Ram 1500 wiring diagram for headlights.

Here's a link to a pdf file containing the headlight wiring diagram for your year model Dodge Ram 1500..
I can't help but notice that you say you've replaced the headlight relay? That's quite odd, because there is NO headlight relay on this vehicle- only a 40 amp fuse located in the power distribution box that sits behind the battery inside the engine bay.
The switch is notorious for burning out because there is NO RELAY on this vehicle, and there is a recall (#819) but this only affects 3500 models even though the headlight wiring is the same for 1500,2500 and 3500 model Rams.
Here are two more links that will help you troubleshoot your headlights problems.
HereInformation on Putting a Relay in the Wiring System

SOURCE: I need the location of MAF sensor in a 1998 Dodge

Your vehicle dose not have a maf sensor. They used a map sensor it is on the engine located under the front of the breater where it attaches to the engine.

SOURCE: PCV valve location on a 2003 Dodge Ram pickup, 4.7?

It's on the side of the Oil filler container.

SOURCE: Remove headlight assembly from a 2001 Dodge Ram

On the upper grill side of the headlight assy. there
should be 1 or 2 push pins that hold the seal on the
headlight assy to the front of the fender. Also check
for a guide/push pin on the inner top of the assy on
the outer fender side. That should be all there is to
hold the headlight in place. Hope this helps.

SOURCE: My 2001 Dodge Dakota pickup, No headlights.

There is a fuse you may have more then one fuse box look under the hood & under the dash. Most of the time Chrysler will just put a number next to the fuses. Go to your owners manual & see what number is your head light fuse. If you still can't find the right fuse take your test light & check both side of each fuse if one side lights up & one side does not replace it with the same size fuse.