With the Trailblazer, the lowbeams shut off if the highbeams are enabled. This is due to several state laws that only allow 2 high beams and no other lights at the same time. The BCM will receive the low beam on signal and high beam on signal from the instrument panel, but due to settings on the BCM will turn off the low beam relay signal and enable the high beam relay signal. However, some people want to have more light when they are driving in the middle of no where. The flash-to-pass option on the car will actually allow you to turn on your high beams without turning off any other lights. This, then, will give us the option of setting up the normal high beam operation the same way.

What you need:

• SPDT switch
• T-tap
• Soldering iron with solder, or fastons

Turn this:

Into this:

First let's look at the flash-to-pass / high-beam switch.

The switch only has 3 connections, 2 signal leads and a connection to ground. From this we can assume that the switch will ground the signal leads when enabled. We also know that the switch is mutually exclusive, since moving the switch forward will turn on the high beams and pulling it towards you will enable the flash to pass signal.

This means that we could connect the high beam signal to the flash to pass signal, so that when we push the switch forward, it will in fact enable flash to pass on the BCM (on board computer) and by doing so will not disable any other lights. But, if you are driving in some areas where this is illegal, it\'d sure be nice to have a switch to turn this on and off.

If we put in a single pole, double throw switch, we can connect the high beam signal (pushing the switch forward to enable high beams) to either the flash-to-pass signal, to enable quad beams, or to the original connection so that the low beams will turn off when the high beams turn on.

The easiest place to wire this is at the BCM, which is the under the big box under the left rear passenger seat (behind the driver seat). Here is a pin out of the connector we need with the information for the 2 wires; this connector is the tan connector that sits on the side of the BCM and right next to it is a grey connector that looks the same except for the color:

^^ This connector is tan, not grey! Do not change any of the connections on the grey connector.

Pin E4
Wire Color YE
Function Headlamp Switch Flash to Pass Signal

Pin F10
Wire Color L-GN
Headlamp High Beam Supply Voltage

Now wire the switch in as described above. To do so we put a T-tap in the yellow wire (make sure it is the yellow wire that leads to pin E4 in the tan BCM C2 connector). Then we cut the light green wire making sure that we have enough room to wire in a switch, again making sure that it does to the correct slot on the tan connector. Then connect the light green wire comming from the connector to one side of the switch, a contact that will enable when the switch is on one side. After this connect the yellow wire to the other side of the switch will be connected when the switch is turn on the other direction. And finally connect the green wiring comming from the body harness leading to the high beam switch to the center connection of the switch which can be connector to either the left or the right contact.