There's lots of info for GU manual torque converter lock ups, but I haven't seen a step by step write up for a GQ here, so I thought I'd share mine, and knowing that some of the earlier members of the site really love photos (and I do too), I took lots.
A huge thanks must go to Chaz http://www.chaz.yellowfoot.org/Lockup%20Trans%20Switch.htm, without him this may never have happened. I used his wiring diagram (made for a GU, but easy to adapt)
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and then he was the one who guessed the stupid mistake I'd made, which caused me so much grief when I first tried to use it. The only modifications I made to his wiring diagram were with the numbering. The TCU terminal numbering on a GQ is different to a GU. Using a GQ wiring chart, the wire on our GQ Transmission Control Unit which sends power to the lock up solenoid is number 22 (a grey wire with a red stripe) and the one that sends power to the inhibitor switch (for the P/N lock out relay) is number 19 and is a white wire. The other numbers I changed were 85 and 86 on the brake light relay, and this was just to make terminal 86 the earth terminal for all of my relays (on my relay sockets #86 is a blue wire).
After deciding to go with a system which cut out when the brakes were applied, and had protection from being accidentally activated when in park or neutral (Chaz's system), the next step was to work out where to fit the various parts.
The photos will tell most of the story of what and how.
Here are most of the parts needed for the system. Four relays, as per the wiring diagram. One to do the actual job of engaging the transmissions lock up solenoid, one to prevent the system from activating when the transmission is in park or neutral, one to deactivate the system when you apply the brakes, and the fourth one working with the brake one as a latching relay. An on off switch with a built in LED. A momentary switch, some wire, some crimps, a flashing LED, an enlargement of Chaz's diagram, and a rough outline of how I wanted the new wiring harness to run. There are also some optional extras. Heat shrink, some 3 in 1 connectors, and a plastic box from Jaycar. The rest of the stuff in the organizer box is mostly for when I upgrade our lights and horn.
The switch to arm the system, and the flashing led to warn that it's active, both needed to be in clear view, and I didn't want to cut into the dash to fit them. The last vacant switch hole below the instrument panel was the obvious place for the switch. The best spot I could see for the flashing LED was in the hole down from the steering wheel on the left.
With a bit of searching I found that a Narva 63021BL switch was ideal because it was the right size for the hole, and has a red LED built into it. If you don't like red, they have LEDs in other colours too. The power for this switch comes from a cable on the back of the fuse panel which is live when the key is on, and runs via a 10amp fuse to the switch.
In our GQ, (carby model) there was a huge cavity under the dash, next to the glove box, up above the TCU. With this in mind I decided to put all of the relays into a box and to put it into that space. This meant that I had to run three wires from the switches (one from the main switch, one from the momentary foot switch, and one from the brake light switch) on the drivers side, across under the dash, to the relays on the passenger side. This shot is looking in the hole where the glove box goes.
I got a heap of sockets for the relays on ebay, way cheaper than anywhere else I'd seen them.
Twitched the wires together as per Chaz's wiring diagram.
Tested it like that, and it worked first go.
Cut the excess wire out, and soldered the remaining ones together, heat shrinking them as I went.
Here they are, screwed into the box, with the mounting bracket fitted to the outside.
I used proper connectors on the wires outside the box, because I didn't want to risk any confusion about which wire went where if it needed to be taken out at some later stage. The box has six wires coming from it, three to the switches on the drivers side, and three going down to join into the wires near the TCU.
Making this bracket should've been dead easy, but it's really hard to measure inside the dash. Took a fair bit of trial and error. I cut it as close as I could, screwed it to the box, tested how it fit, cut it a bit smaller, tested again, then bent it a bit, then held it in place and marked where to drill the mounting holes in it.
Even finding which bolts to use took some doing. I had to use the holes which were already there because I don't have a right angle drill attachment. These are really short and fat.
