This happens because someone cheaps out on the metal used on the contacts. If the harness was repaired under the recall and the pump wasn't, then it's possible only half the problem was fixed heading towards the same problem happening again. Even worse, if the connectors on the replacement harness aren't much better than the original ones.

Burnt Fuel Pump Wires
 

Deoxit pro gold! Any contacts. I've literally measured a 160x improvement with two drops of the stuff In a maglite contact!


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I bought a new harness (61-12-9-387-439), stripped some new wire, and redid the connection. I put heat shrink over the connection, and also electrical tape over the heat shrink.

The car does not hesitate when going uphill anymore. However, the wires are slightly warm to the touch. Is the warmth normal?

Again, the critical part is the connection, if the pump side of the connectors are poor quality and/or oxidized you still might have a problem.

Crimps/soldering needs to be done properly as well.

I am assuming you are talking about the socket that plugs into the pump? The part number that I included in the last post includes the socket. So it is new.

I soldered the wire. I first twisted the stranded wire, then tied it in a Western Union knot. I then put solder over that. After that, I head shrunk the connection.

Usually the warmth is from the connection. Did you apply any connection help? Deoxit Gold is the best I've been using since the 90s.

No connection help, just Western Unioned the wires, soldered, and heat shrunk it.

https://imgur.com/a/6UKKFPa