I found the two posts on manual tc lock-up.
TC Manual switch.......
Hold on fellers!!!!!! I Just performed the mod today. Pretty simple but I am a trans man and there are some things that I want you to understand prior to beginning this operation. You only want this mod to be energized or the switch to "on" at speeds over 40. If you forget to turn it off before stopping, the vehicle will shutter violently and you can leave parts of your trans or motor behind. Dont Get me wrong, I love this mod but I suggest that this mod is only for the guy who drives long distance and not Stop and Go. This mod will save you from smoking your convertor if your vehicle is cycling lock up on and off irregularly. I will soon have BOSS Transmissions website back on line and the ability to post a diagram relating to this mod. Look for a new thread detailing the mod called "E40D lockup Modification"
For those who would like to convert there lockup to a manually controlled status via a two pole switch, the following will apply.
I post this information for peeps that Who do not want to entirely reverse engineer thier lockup circuit. Thus was the case on one of the vehicles brought to me. This mod was performed and works like a charm on an ambulance that had intermitten lockup problems. Intermitten lockup causes heat and convertor failure. Ideally in this situation the vehicle could be diagnosed by Ford with minor difficulty. However, It is my luck as is some of yours that the problem cannot be picked up my scanning the rig for faults. Poor grounds or dirty connections do not display themselfs on scanners. This vehicle we worked on has a 9"x6" wiring harness in it. The process of reverse engineering that bad dog was unacceptable so we went to Ford. After shelling out big bux to Ford to say "we dont know where the problem is but we can keep working on it (for 65 per hour!)" We decided to mod the trans harness ourselves. You should have a multimeter available to you before performing this mod.
The E4OD in my opinion shifts like crap from the factory. lockup engages in all gears somewhat randomly and really gives unpredicatable results in shift feel. There is a solution but it is not for everyone. Several companies make trans command adapters which work nicely if everything in the vehicle is electrically tight. If there are connection problems in the vehicle regulating lockup circuit the trans controllers will not work. So the only other option in curing this problem of shift feel revolving around intermitten lockup and wireing problems is to install a manual switch to bypass the computer controlls for this circuit. DO NOT LET THE WIFE OR KIDS OPERATE THIS VEHICLE WITHOUT THIS SWITCHED MARKED "KEEP THIS SWITCH OFF." If this switch is left on below the speed of 25 the vehicle will shake and you may leave parts of your trans or engine behind!! This Switch cannot be placed in the "on" position until the vehicle speed is above 35 for most effective shift feel and control. For guys that want that control over shift feel this really does work great and should improve mileage for those who experience lockup cycling. Lets begin.
Identify the Main electronic harness going to the trans. Above the trans connector about 4-5 inches locate the Purple wire with a white or Yellow stripe on it. This wire gets stained with oil so look closely. Simply cutting this wire will make the trans shift through all the gear ranges except for convertor lockup. The trans will at this point shift better then u have ever felt before because the gear ratios are all nicely matched by ford. Early lockup screws up this nice ratio thus this fix will eleminate this.
Now that the lockup wire is cut attatch 2 lengths of wire to the two wires that are now available at the trans (one length per each lead).
drill a small hole in the floorboard under the carpet to get the two wires up to your dash somewhere convient for a switch. At this point u need to do a test. Tie these two wires together. The trans should operate normally and lockup will come in as before you cut the wires. At this point all we created was a loop effectively lengthening the path of the convertor lock up circuit. Using your meter, and a second driver for the rig, get up to about 55 mph and hold steady. Set your meter to dc voltage on the 20 volt scale. Place your red lead to the two wires on your dash that are tied together and the black lead to the outer circle of your cigarette lighter (ground). At the speed of 55mph with the vehicle warm you should have a reading of about .5 to 3 volts. If you apply the brake and hold the speed at 55 you should see that voltage jump to 12-14 volts. If you let off the gas the voltage should be 12-14 volts. As you get back on the gas and return to 55 and level out you should see the voltage drop to .5-3.0 volts. With the vehicle in park the voltage should again be 12-14 volts. You will notice that when lockup engages the voltage drop occures and lockup takes place. We are going to manually drop this voltage by adding a ground which is effectively what the computer does to engage lockup. If these results are not typical of your vehicle STOP HERE!! Your harness may be different and this Mod will not apply to your vehicle.
Assuming your tests indicated the correct results and u have the two wires inside your vehicle, open up the two wires you tied together and place the red lead on one of those wires and the black lead to the cigarette lighter outer ring (ground). You should notice that one lead will produce 12-14 volts with engine on and in park and one wire of the two will produce .5-3 volts when measureing to ground. Note the High voltage lead. Take your switch and place the high voltage lead reading 12-14 volts on one of the switches poles and tighten it down. On the other side of the switch connect the remaining wire from the trans AND a jumper wire that is somewhere securely grounded to the chassis of the vehicle. This will in effect ground the second terminal to the chassis. The benefit of this arrangement will gives the driver total control of lockup. Notice that when the switch is open (off) the computer cannot engage lockup if it is undesireable to the driver and around town you will get nice crisp shifts that contain nice ratios as designed by ford. Once this switch is activated lockup will engange and HOLD for the duration the switch is on.
I recommend you only use the switch for highway use to increase economy. That is unless your like me, I like the ability to control shift feel and it doesnt bother me to toggle that switch off and on for stops. If your a control freak this is the nuts and works well. This mod was performed on a 91 Diesel ambulance converted to a service truck. As we have not tested it on all electrical configurations for each of the years we cannot assume that this mod will work in all applications. For those of you that it does work for, Enjoy....its a really nice feature that will payoff in economy. On the highway flip the switch and let her go!!! even if you let off the gas a little lockup wont fall out and then reengage like the factory controls. Once Boss Transmissions web site is back up we will provide schematics for those who would like to review the above procedure.
We make no claims about its intent or use. Perform at your own risk. Feel Free to Correct anything I have said here. Read this Thread thoughly incase others experience situations that are undesireable. Thanks for your time..
Dan from BossTrans
.......When I did my mod, I located where the trans harness comes up into the engine compartment. If you look on the drivers side inner fender you will see a harness that that comes up from the frame and splits into three, with three connectors (the connectors are attached directly to the inner plastic fender). The connector with the purple/yellow needed to perform this mod was in the connector closest to the front of the truck. The wire was on the bottom row of holes in the connector and the second one in line. I followed the wire back a few inches and cut it and spliced my lengths of wire there. Originally i just put the switch on those two wires, so "off" would be no lock-up and "on" was normal factory set-up......I have since went to the way they described in the post. I hope this helps. If more clarification is needed just post back.