Depress the locking spring where indicated to release and fasten H4 Bi-xenon bulb.

Bi-Xenon HID headlight Kit Installation
Connect ( + ) lead of kit wire to the ( + ) battery terminal.
Also Connect ( - ) leads (2 of them) to existing bolts near the headlamps.  

NOTE:  "O" ring of  ( - ) lead must touch metal  to ground properly (not rubber / plastic).
Remove stock headlight bulbs and replace with bi-xenon kit bulbs.
Vehicle's Headlamp Plug
Plug 4
Step 1: Fasten the bi-xenon kit's power wire.
Step 2: Install the Bi-Xenon kit bulbs
Plug 3
Ballast to
Bi-Xenon bulb
Plug 2
Ballast to Bi-Xenon bulb
Plug 1
Power Wire to Ballast
Step 3: Plug-in the rest of the wiring
Step 4: Test Headlights
(other end of wire from step 1)
Bi-xenon HID Kit installed on 2007 Tacoma
2007 Tacoma with Bi-Xenon HID Kit
An existing bolt near the headlamp can be used for grounding.
After removing stock bulb, Unplug it from the stock headlamp harness (brown).
There is only one red / positive wire, it will connect to the battery on the positive terminal.
H4 bulbs fasten with  locking spring.
Plug Directly into Stock Headlamp Harness
There are TWO  ballasts included with the bi-xenon HID Kits
Stock Toyota Headlamps
2007 Tacoma headlights BEFORE.
Bi-xenon HID install page