1998 TJ, airbag light comes on and radio, heater blower, turn

sounds like it could be a bad flasher and for the fan there is a fan relay i would suggest checkin that out

Don't know how the ABS light would be related to the blower motor, you said you checked everything - did you check the blower motor circuit for power and ground with a meter or a test light ?
Is the resistor getting power from the relay ?

Check to see if u have power & ground to the blower with the fan on.if so u need A blower mtr

Get a schematic and trace out the power source to those devices not working.

The rear blower and the brake lights might not be related troble. The rear blower has a ballast resistor that can fail and it's next to the blower motor in the rear heater housing. The blower motors are also known to go bad so wrapping on it with it turned on might( wake it up) and it'll start woring again as a poor connection shaken or the worn motors brushes shaken down where they make connection again. Then you say the rest of the lights work do you mean that the brake light bulbs come on with the hazard swich entergized? or do the rear lights just light yellow turn lights only? I'd check or even replace the brake light buld=bs before I'd do anything else.their are other things that don't work if the fuses were involved and the same goes for the heater rear blower as the front blower uses the same fuse.

sounds like you have a wire that is touching something not supposed to be or a blown fuse or a tripped relay have to take out radio see if power comes back if does look for wire causing messed up signal check your radio relays

Had the same thing with my 2004 Wrangler. The Airbag light stayed on also. Took to dealer - Cost $400 for them to replace the ignition. Fixed every thing.

Have you checked the fuse? The blower fan has a resistor that controls the speed in the air box by the passengers feet. When the heater core was replaced, something could have happened to the connection or wiring. Not sure why the radio would be affected by the same thing, could be a coincidence or something dislodged under the dash. Start at the fuse and go from there.

Below is a listing of which fuse corresponds with which circuit:

1 - 10 Amp - Transmission Controller, Gauges, Autostick
2 - 10 Amp - Right High Beam Headlight
3 - 10 Amp - Left High Beam Headlight
4 - 10 Amp - Radio, CD Player
5 - 10 Amp - Washer Motor
6 - 15 Amp - Power Outlet
7 - 20 Amp - Tail, License, Parking, Illumination Lights, Instrument Cluster
8 - 10 Amp - Airbag
9 - 10 Amp - Turn Signal Lights, Turn Signal/Hazard Indicator
10 - 15 Amp - Right Low Beam
11 - 20 Amp - High Beam Relay, High Beam Indicator, High Beam Switch
12 - 15 Amp - Left Low Beam Headlight
13 - 10 Amp - Fuel Pump Relay, Power Train Control Module
14 - 10 Amp - Cluster, Day/Night Mirror,Sunroof, Overhead Console, Garage Door Opener, Body Control Module
15 - 10 Amp - Daytime Running Light Module (Canada)
16 - 20 Amp - Fog Light Indicator
17 - 10 Amp - ABS Control, Back Up Lights, Daytime Running Lights, A/C Heater Control Cavity Fuse Circuits
18 - 20 Amp - Power Amplifier, Horn
19 - 15 Amp - Overhead Console, Garage Door Opener, Trunk, Overhead, Rear Reading, and Visor Vanity Lights, Trunk Release Solenoid, Power Mirrors, Power Door Locks, Body Control Module, Aspirator Motor
20 - 20 Amp - Brake Lights
21 - 10 Amp - Leak Detection Pump, Low Rad Relay, High Rad Relay, A/C Clutch Relay
22 - 10 Amp - Airbag
23 - 30 Amp - Blower Motor, ATC Power Module
24 - 20 Amp - Power Window Motors
25 - 20 Amp - Power Door Lock Motors, Power Seats

I had a similar problem with my 2000 Jeep TJ and I found the problem in the wiring harness under the hood.several wires were corroded and almost burnt off.If you remove the black tape which keeps the harness bundled together and if you see evidence of "green" type powder or "gook" it's most likely where the wires have faulted.