Headlights go off and on on their own and when this happens it is like turning them off and right back on. the radio and interior lights go out also.

The door switch is located inside of the door latch. You probably have a bad switch and need to have the latch changed. Since the drivers door gets the most use, that is a good place to start.

1 - Heated washer nozzles, heated outside mirrors 10A
2 - Turn signal system 10A
3 - Illumination 5A
4 - License plate light 5A
5 - Comfort system 7.5A
6 - Central locking system 5A
7 - Back-up lights 10A
8 - Telephone system 5A
9 - ABS 5A
10 - Engine control, gasoline 10A
11 - Instrument cluster, shift lock 5A
12 - B+ (battery positive voltage) for DLC 7.5A
13 - Brake lights 10A
14 - Interior lights, with central locking 10A
- Interior lights, only 5A
15 - Instrument cluster, automatic transmission 5A
16 - A/C-clutch, electrical water pump 10A
17 - Door lock heater 7.5A
18 - Right headlight, high beam 10A
19 - Left headlight, high beam 10A
20 - Right headlight, low beam 15A
21 - Left headlight, low beam 15A
22 - Sidemarker lights, right 5A
23 - Sidemarker lights, left 5A
24 - Wiper system, washer pump 20A
25 - Fresh air blower, air conditioning 25A
26 - Rear window defogger 25A
27 - Daytime running lights 10A
28 - Fuel pump (FP) 15A
29 - Engine control, gasoline 15A
- Engine control, diesel 10A
30 - Sunroof 20A
31 - Automatic transmission 20A
32 - Engine control, injectors, gasoline 10A
- Engine control, injectors, diesel 15A
33 - Headlight washer system 20A
34 - Engine control 10A
35 - Trailer socket 30A
36 - Fog lights 15A
37 - Radio system 10A
38 - Luggage compartment light, central locking system 15A
39 - Emergency flasher system 15A
40 - Dual horn 20A
41 - Cigarette lighter, 12V power outlets 15A
42 - Radio system 25A
43 - Engine control 10A
44 - Heated seats 15A

Do you have the right battery installed? if not and it is a higher voltage, this will happen.

I take it you mean that the radio stops working completely once the headlights are switched on. So if you sit in the car during daylight hours and turn the lights off and on, the radio does the same except the other way round (lights off, radio on). Have I got that right?
It cannot be the fuse because the radio wouldn't work at all if it had blown. The wiring may well be the problem. Something is either shorting or I am thinking that there is not enough power (for whatever reason) to run both lights and radio at the same time, although the battery draw on a radio is relatively low. Is your battery charging correctly? Does it happen if you open all doors and the interior lights operate. Try opening all the doors and turning headlights off and on. Do the interior lights turn off and on like the radio does?

check the battery connections for corrosion. clean and reinstall. also have checked for ground related issues.

Check the fuse box on the right (passenger) side of the center console. You should be able to identify which fuse it is by checking in the owner's manual.

Fuse Locations & Functions
1. Washer nozzle heaters, glove compartment light (10A).
2. Turn signal lights (10A).
3. Fog light relay, instrument panel light dimmer switch (5A).
4. License plate light (5A).
5. Comfort system, cruise control, A/C, steering wheel module (7.5A).
6. Central locking system (5A).
7. Back-up lights, speedometer vehicle speed sensor (VSS) (10A).
8. Open
9. Anti-lock brake system (ABS) (5A).
10. Engine control module (ECM): gasoline engine (10A)
11. Instrument cluster, shift lock solenoid (5A).
12. Data Link Connector (DLC) power supply (7.5A).
13. Brake tail lights (10A).
14. Interior lights, central locking system (10A).
15. Instrument cluster, transmission control module (TCM) (5A).
16. A/C clutch, after-run coolant pump (10A).
17. Open.
18. Headlight high beam, right (10A).
19. Headlight high beam, left (10A).
20. Headlight low beam, right (15A).
21. Headlight low beam, left (15A).
22. Parking lights right, side marker right (5A).
23. Parking lights left, side marker left (5A).
24. Windshield washer pump, windshield wiper motor (20A).
25. Fresh air blower, A/C (25A).
26. Rear window defogger (25A).
27. Motor for rear windshield wiper (15A). (if equipped)
28. Fuel pump (FP) (15A).
29. Engine control module (ECM) gasoline engine (15A)
30. Power sunroof control module (20A).
31. Transmission control module (TCM) (20A).
32. Injectors: gasoline engine (10A)
33. Headlight washer system (20A).
34. Engine control elements (10A).
35. 12 V power outlet (in luggage compartment) (30A).
36. Fog lights (15A). (if equipped)
37. Terminal (86S) on radio, Instrument cluster (10A).
38. Central locking system (w/ power windows), Trunk light, fuel door, Trunk lid (15A).
39. Emergency flashers (15A).
40. Dual tone horn (20A).
41. Cigarette lighter (15A).
42. Radio (25A).
43. Engine control elements (10A).
44. Heated seats (15A). (if equipped)

Fuse arrangements in fuse bracket/battery:
S162. Glow plugs (coolant) (50A).
S163. Fuel pump (FP) relay/glow plug relay (50A).
S164. Coolant fan control (FC) control module/coolant fan (40A).
S176. Relays panel interior (110A).
S177. Generator (GEN) (90 Amp.) (110A). Generator (GEN) (120 Amp.) (150A).
S178. ABS (hydraulic pump) (30A).
S179. ABS (30A).
S180. Coolant fan (30A).

possibly the dimmer switch on the floor? happened on my 91 half ton dims didnt work but brights did and then they cut out altogether. a little water goes a long way

it should be number 42


MKIV FUSE LIST
1. Washer nozzle heaters, glove compartment light, memory seat control module (10A).
2. Turn signal lights (10A).
3. Fog light relay, instrument panel light dimmer switch (5A).
4. License plate light (5A).
5. Comfort system, cruise control, Climatronic, A/C, heated seat control modules, automatic day/night interior mirror, control module for multi-function steering wheel, control unit in steering wheel (7.5A).
6. Central locking system (5A).
7. Back-up lights, speedometer vehicle speed sensor (VSS) (10A).
8. Open
9. Anti-lock brake system (ABS) (5A).
10. Engine control module (ECM): gasoline engine (10A); diesel engine, Model Year 2000 > (5A).
11. Instrument cluster, shift lock solenoid (5A).
12. Data Link Connector (DLC) power supply (7.5A).
13. Brake tail lights (10A).
14. Interior lights, central locking system (10A).
15. Instrument cluster, transmission control module (TCM) (5A).
16. A/C clutch, after-run coolant pump (10A).
17. Open.
18. Headlight high beam, right (10A).
19. Headlight high beam, left (10A).
20. Headlight low beam, right (15A).
21. Headlight low beam, left (15A).
22. Parking lights right, side marker right (5A).
23. Parking lights left, side marker left (5A).
24. Windshield and rear window washer pump, windshield wiper motor (20A).
25. Fresh air blower, Climatronic, A/C (25A).
26. Rear window defogger (25A).
27. Motor for rear windshield wiper (15A).
28. Fuel pump (FP) (15A).
29. Engine control module (ECM) gasoline engine (15A); diesel engine (10A).
30. Power sunroof control module (20A).
31. Transmission control module (TCM) (20A).
32. Injectors: gasoline engine (10A); diesel engine (15A).
33. Headlight washer system (20A).
34. Engine control elements (10A).
35. 12 V power outlet (in luggage compartment) (30A).
36. Fog lights (15A).
37. Terminal (86S) on radio, Instrument cluster (10A).
38. Central locking system (with power windows), luggage compartment light, remote/fuel tank door, motor to unlock rear lid (15A).
39. Emergency flashers (15A).
40. Dual tone horn (20A).
41. Cigarette lighter (15A).
42. Radio (25A).
43. Engine control elements (10A).
44. Heated seats (15A).
Fuse arangements in fuse bracket/battery:
S162. Glow plugs (coolant) (50A).
S163. Fuel pump (FP) relay/glow plug relay (50A).
S164. Coolant fan control (FC) control module/coolant fan (40A).
S176. Relays panel interior (110A).
S177. Generator (GEN) (90 Amp.) (110A).
Generator (GEN) (120 Amp.) (150A).
S178. ABS (hydraulic pump) (30A).
S179. ABS (30A).
S180. Coolant fan (30A).