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Message: <blockquote data-quote="Mustang5L5" data-source="post: 1541997" data-attributes="member: 30520">Decided to play around with this tonight and check the wiring out.   Now, this won't really apply to method #1 if you swap the board.  This is really a watchout in case you decide to perform the PATS programming (or PATS delete) and just swap the entire cluster over.  I think the benefit here is the speedo will operate correctly, but the downside is no mileage match.But regarding Method #2, there is some wiring difference that you need to pay attention to.  Specifically the defrost wiring into the cluster.  Not sure if Ford decided to relocate the timing circuit to the cluster, but when you press the defrost button on a 01-04, a signal goes to the cluster and then another wire out to the relay.  Assumption here is the timing circuit is in the cluster.SO poking around, i found that this wiring is non-existent in the 99-00 harness.  If you scroll up to post #2, the wire locations marked "NOT USED" do not have a wire present at all.  Likewise, i managed to snag a couple connextors from a junkyard 01-04 car, and confirm that the 01-04 wiring diagram is accurate.   What this means is the low-coolant wire is missing, but the two defrost wires are present.   Long story short,  the diagrams in post #2 are correct.   Surprise surprise.So, had to do a test.  I plugged in the 01-04 cluster harness ends and tested continuity between the two defrost wires.  (pin 9 and 10, small plug).   I had zero continuity.  That means what whatever happens inside the cluster is controlled and activated by something.  My guess, power on allows the circuit to close when the defrost on wire is energized.Next, i took the 01-04 cluster plugs and plugged it into my 99-00 cluster.  I tested continuity and had it between pin 9 & 10.   Now, i don't have a circuit diagram, but I would make a reasonale assumption that having these two wires always in continuity probably isn't going to cause a desirable outcome.  I had read about folks having a constantly on defroster, and now see why.SO, long story short.  If you are going with method #2 and performing the PATS reprogram/delete, you will really want to pay attention to your clusters.   99-00 cars should use 99-00 clusters but they might be able to use a 01-04 cluster because they completely lack the wiring for the defrost.  However they also lose the low coolant light for good.   01-04 cars should only use an 01-04 cluster because the 99-00 clusters will short the defrost wires and possibly cause a drain issue or even blown fuses.  You can remove this wires and make the defrost inop if you want.  Might be other solutions but that's beyond the scope of what I'm doing here.CLiffs Notes for Method 2 (Pats reprogram/delete)99-00 cars should seek a 99-04 cluster,  possible can use 01-04 cluster but no low coolant light01-04 cars should only use 01-04 clusters.</blockquote>