How is the converter lockup solenoid on a 1984 Pontiac Sunbird J2000 activated?

You got the two wires, measure the resistance of the solenoid maybe you have a bad solenoid.

Probably because it's not the solenoid causing the draw. It can be something else in the circuit including possibly the PCM.

Also, one of the wires inside the transmission could be grounded. The coil will still read normally between the two pins. Besides continuity, measure each pin to ground.

If you DO find one pin grounded, you might try switching the positions of the two wires in the connector. Instead of blowing fuses, I think the solenoid will engage all the time of it is switched on the ground side.

If it is switched on the positive side, which it sounds like since it doesn't blow the fuse until it's time to activate it, it might work fine that way. Logic would dictate if there was no switching done on the ground side, they would ground it inside the transmission and just have the one wire in the electrical connector, but they might have designed it this way for some other reason.

Wrenchtech will correct me if I'm wrong, but I don't THINK any switching is done inside the transmission. If that were the case, all they'd need outside would be to apply battery voltage when the ignition switch is on. The reason for getting the Engine Computer involved is to add control for other variables. Examples would be to instantly unlock it when you tap the brake pedal in preparation for slowing down. The transmission wouldn't know that. Lockup doesn't occur when the transmission fluid is cold. The Engine Computer goes by coolant temperature. When a computer switching circuit is used, it's easy to pulse the solenoid during engagement to ease it in without a thump or clunk. Can't do that with a simple switch.

These are just things going through my mind that might help. Also, is that 20 amp fuse you're blowing in the car's fuse box or in your jumper wire? If it's in the fuse box, the computer can shut the circuit down to protect its switching circuit from damage. That type of solenoid shouldn't draw more than probably 3 - 5 amps. There are similar fail-safes for some sensor circuits on many cars. If you even momentarily short the 5 volt or 8 volts supplies to ground, the voltage will stay at 0 volts until you cycle the ignition switch off and back on to reset it, but it won't blow any fuses. It would stand to reason the lockup circuit would be protected the same way. You're bypassing that safety circuit when you use jumper wires.

Just out of curiosity, what happens if you switch the wires around when you're using jumper wires? Does the fuse still blow?

This solenoid works like all the others in the car. It gets a constant power feed and the PCM controls is by applying ground with a quad driver.
I suspect your short is something not even connected with this circuit. This circuit is protected with a 20amp fuse and there is no way that much is needed just for that solenoid so I suspect that fuse also powers other things and one of the other circuits is where the problem is.

If you give me the location and exact ID of the fuse, I will try to see what is on the circuit.

I hope Wrenchtech has an answer because I'm interested too. I have the same setup on my '88 Grand Caravan. I use it at a minimum of once a year to drag a tandem axle enclosed trailer to the nation's second largest old car show swap meet 55 miles from my house. That trailer is bigger and heavier than the van. Stopping is no problem without using the trailer brakes but the wind resistance makes it impossible to hit 70 mph going down a very steep 3/4 mile-long hill. By the time I'm half way there or half way home, the engine is running warmer than normal, (it's also the weekend after the 4th of July), and the lockup function kicks out at anything over 1/2 throttle. If I let up on the gas to keep it locked up, I lose speed and become a nuisance on the freeway. By the time I hit the city it won't lock up at all.

I've been watching this post because I've toyed with the idea of adding some isolation diodes and putting a manual switch on the dash to keep the solenoid energized. The reason to kick the lockup off is to get increased fluid flow through the transmission cooler, but it's assuming there's a problem based on engine coolant temperature. There is no temperature sensor in the transmission. '88 was the last year for the indestructible hydraulically-controlled transmission. In '89 they went to the miserable computer-controlled transmission and that one would explode pulling the trailer before I got to the end of my driveway.

Your '84 is also hydraulically-controlled but I don't know if there's a temperature sensor incorporated with the solenoid. My guess is the Engine Computer will kick the solenoid off, like mine, when the engine gets too warm, or when the throttle is nearly fully released. You might look for intermittent dropouts in your throttle position sensor as the cause of the lockup kicking in and out. When I release my gas pedal then press it again, the tach goes up another 200 rpm, then drops back down one or two seconds later when it re-engages. That's based on throttle position.

If there's a short with the solenoid that can blow a 20 amp fuse, I don't think the computer would ever be able to engage it. It might try but if you ever feel it lock up, there would have to be no short.

Something else you might consider is connecting a test light to the solenoid wires coming from the computer and watching what it does when lockup is supposed to occur. If it simply switches on and off, a digital voltmeter will work too, but if it modulates it for a smoother application, that will be hard to see with a voltmeter because the voltage will go from 0 to 12 volts on and off rapidly for a fraction of a second. The voltmeter won't display that average but a test light will flicker rapidly or just be dim during that time. My guess is it would be easier to build a small accumulator in the transmission to ease the clutch engagement and just put a simple on / off switching circuit in the transmission, but the engineers seem to want to complicate anything they can think of with more sophisticated electrical circuits, so it's hard to say.

I have no idea where you're at now. We just don't cut wires and try to drive it. The computer will recognize that the solenoid is not connected and I have no idea what it's programmed to do at that point. That's just not the way a tech would approach this and to tell you the truth, I have no idea what you have done at this pointy so I'm going to back out of this and see if anyone else wants to get involved. Simply reading the resistance of the solenoid will tell you if it's shorted or not.