[bailey08]

I have a 2002 GV auto, I want to be able to lock up the torque converter manually when off road to enable engine braking for downhill work.

The TCC gets +12v from the ecu and earths out through the gearbox.

I have already hooked up a LED just to see when the TCC is locking up, I'm going to add a red LED and switch to manually over ride what the ecu wants. I'm also going to add a diode so there's no back flow of power to the ECU and it can still work and do it's thing (not sure if I need it).

Just after some general comments if it's worth doing it and will it cause any damage.

I've added some pics for reference and incase other want to do the same.

[JrZook]

From the electronic side of things what you proposed will work. Just make sure the current rating of your diode is sufficient and remember your current limiting resistors in-line with the LED's if their not 12V rated.

[bailey08]

I hooked it all up. The check engine light comes on when i flick the switch so there must be some other sensor involved as well or maybe cause i'm using a diode the ecu thinks thre's no tcc connected.

I can hear the solinoid working with the car turned off.

when driving I'm positive it can't lock up in 1st or reverse. If i take off (with minimal revs as i don't know how strong the tcc is) with it switched on it takes off normally but once it hits 2nd it labours the engine (as i'm using minimal revs) as with 3rd and forth.

[royce]

A better way may be to use a change over relay

cut the TCC wire, auto side of it to pin 30, ecu side to pin 87a, pin 87 to 12v, pin 85 to earth, pin 86 from your switch

also consider using a switch with an indicator light, be easier than stuffing around with an LED and resistors

But now the reason why you shouldn't do this

Look at a torque convertor, its a massive thing, designed to cope with shifting all the power from the engine into the transmission, in comparison the lockup is a piddly little thing, designed to lock the convertor 'fans' together under very small torque and throttle loads, subjecting it to the extra load of either accelerating or engine braking (especially in low range) will likely either break it or shorten its life pretty drastically

[joeblow]

I was under the impression that the tcc was engaged when in 4x4, hence why the t/case has a high and low switch hooked up to it.