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[M.L.S.C.]

The wire is indeed purple with a yellow tracer, there is only one of those in the harness, the other one Fozz is talking about has a different color tracer. Factory settings of the PCM command a converter lockup shortly after upshift to 3rd (feels like another shift), and nearly instant lockup upon upshifting into OD (that one can't be felt easily). If you accelerate at moderate throttle you'll count 4 upshifts: 1->2, 2->3, 3->3lock, 3lock->4lock. PCM commands converter unlock under heavy throttle (3/4 throttle or so), upon complete release of throttle pedal, whenever brakes are applied, and upon downshifting into 2nd gear. I run a manual switch for two main reasons:
- I hate the 3lock->4lock upshift at 35mph, it drops my engine speed down to nearly 1100 rpms, which combined with an uphill makes for lots of smoke till I hit 1600 rpms.
- upon release of throttle and converter unlock there's little to no engine braking available, leading to heavy used of wheel brakes on long downhills and potential glazing and burnup of pads and shoes. I have my converter wired up to a switch on my shifter, I also have the OD control button moved to the same location ('89-'91 trucks have the darn thing on the dash, very stupid idea IMHO), so I can operate both with the same hand and very quickly. I have a SPDT (5-pole) relay wired in the converter wiring between the transmission and the switch on the shifter, the relay is triggered by the BOO switch and opens unlocks the converter for me whenever I hit the brake pedal. If often manual switch operation is expected, a "dummy converter" must be created and it's signal must be fed back to the PCM to prevent it from detecting a converter circuit failure and entering "limp" mode - I have my PCM totally disconnected from my converter, I feed the PCM 12V key-on through a 22k-ohm resistor and it is very happy with it and leaves me and my manual converter switch do our thing. Additionally, the 35-40mph threshold Fozz mentioned is a bit high, I run around town with the OD off and converter locked like all the time - above 30 mph and I lock it up, under 30 mph and I unlock. Overall I'm loving the manual lockup switch, I drive over some 8% hills and going downhill idling at 2400 rpms in 3rd gear with the converter locked allows me to safely maintain speed without ever touching the wheel brakes, which means that unlike the gassers who ride on the brakes all the way down when we hit the bottom of the hill I have nice and cold brakes and I can stop on a dime, while they have severely degraded braking performance cause everything in their wheels is about to start glowing