2002 Dodge Neon 20 amp FP/ASD fuse #21 keeps blowing

That fuse also powers the Auto Shut Down Relay so unplug it first then see if the fuse blows, if yes the only other place it goes is to the ECM so unplug it next, if the fuse still blows check the wire. I hope this helps, take care. If you have any more questions about this vehicle or just want to say hi, send a testimonial.

There are two fuses for the fuel pump relay. One fuse is load side of relay, that fuse also sends voltage to load side of asd relay, the asd relay sends voltage to several systems, two of which are the fuel injectors and ignition coil. I'm not telling you to replace, anything, but, you need to do some testing.
The other fuse goes to control side of relay, smaller amp fuse. I don't know the amp rating of the fuse that keeps blowing.
See that fuse, it supplies voltage to load side of fuel pump relay and also to asd relay.

Check to see if there is power to the injectors. They are fed from the same fuse and relay. If there is no fuel pressure than the fuse would be the fist suspect sin the ASD and fuel pump relay are fed off the same fuse. The fuse is fuse 21 in the power distribution center.

If the fuse is good try swapping the ASD relay with another relay in the fuse block that is the same. If you know have spark than replace the ASD relay.

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Unplug the blower motor & see if the fuse blows

Then you know the answer or continue to other
items in that circuit

Both. If the running lights ( marker, tail, clearence, or parking) and brake lights are out since the rain, a tail light assembly is broken and filling with water enough to create a short to ground. If there's no broken lens, whitch normally only blows the bulb. Then, the problem lyes in the trailer light harness. the brown wire (tail) & green wire (left turn/brake or yellow wire (right turn/brake) must be bare exsposed that shorts to ground when wet. all the trailer wires could be smashed together damaged the plastic coating on them. no problem till water shorts to ground. The white wire is the ground wire make its not able to touch the other 3 wires or bare & wet. Tape wires seperate then replace tail/mkr fuse and brake fuse. That should do it.

If the ASD blows the fuel pump fuse the fix is easy disconnect the battery go the the 02 sensor the one near the power steering pump here is the scenerio your 02 heater circuit has shorted to ground you will have to unravel the o2 harness you did add a year so i will assume its a 95 use this as a guide do you see the 02 heater and the nearest ground is the 02 sensor which can cause FP to blow open

Must be a short in the wires

The wattage of the new headlight bulbs may be to great and exceeding the amperage limit of the fuse.

hmm. lt look like there are poor joints in your wiring specially the groung wire. check the diagram of your auto. check the unit diagram for which the fuse blows. usually the fuse blow when there is a short circuit. if you look around you will find it.
good luck
ehsan.