Landcruiser V8 Auto Touque Convertor Lockup

Norm,
You have basically got it right. The main function of the lock up feature is to keep the converter and transmission cool when in overdrive. You’ll find all four speed or overdrive equipped auto’s use lockup converters. Overdrive creates a large amount of slippage in the converter which generated too much heat, particularly at lower vehicle speeds. Some transmissions won’t go into overdrive without locking and this makes the transmission just as efficient as a manual when the converter’s locked.

I’m not familiar with the LC100 auto’s wiring, but you’ll need to look at the circuit diagram and find the wire from the transmissions control unit to the converter control solenoid. Then you could use my circuit and do it in a similar way that I have.
This method allows you to hold the converter locked for maximum engine braking on downhill descents as well as unlock it every time you stop to avoid stalling your car. I’m not sure if these features are beneficial to you because I don’t think the LC100’s transmission can lock in 1st gear.
To do it you only need a few relays and switches, I think all up it only cost me around $60 and a few people on the forums have had it done by an auto sparky for around $120, using my circuit.
Chaz

Norm and others,
I would suggest using caution when attempting to interface to the 5 speed A750 (I think) auto in the LC100 or Prado without a tested solution. Experts advise that the unit uses fairly sophisticated -ve and +ve switching and you need to be confident that any small switching breaks (moments when relays are changing over) won't garble the computer control or cause unimagined grief or processor lockups.
The concept is good but I would wait for someone to do the hard yards and have a tested product. The guys at Wholesale automatics in Victoria have not done one of these units yet.
Anoldbuddy

I often change gears with the converter locked, but I suspect that your cruise control is dropping the gears back because it’s trying to maintain a speed that you’ve set. Cruise control isn’t very efficient, particularly in hilly terrain. Good on the flat, but you’ll use much more fuel in the hills.
I think Toyota wouldn’t endorse this modification and dishonor your warranty. I did this to my Patrol shortly after it was new, but Nissan wouldn’t have had a clue that it was there. I switch it off when it goes in for servicing. Now with over 90,000km on the clock, it’s out of warranty, but still performs brilliantly.
Chaz