I grew tired of removing my TPMS from my under dash power outlet every time I parked my truck, and then having to fish it out from under seat to plug it back in. So I spent some time with the wiring diagram and came up with an easy way to switch the two under dash outlets to a acessory/run power (shuts off when key is off)
I obtained a fuse tap for mini fuses from advance auto. I used my bench grinder to narrow the male spade terminal of a solderless connector so that it would fit into the fuse box.
I then cut off the solderless connector that came with add on tap. Crimped on the modified male connector and installed a 7.5amp fuse to the top slot only.
I prefer to error on the side of caution -- I only use these two outlets for the TPMS reader (0.015Amps) and phone charging -- 7.5 is probably still more than I need. The circuits I am working with in the fuse box are 15 and 20 amp circuits so I could go even higher.
I removed the 20amp Accessory power outlet fuse in rear fuse box (fuse #46) I did my research and this fuse is used only for these two outlets. The cigarette lighter is a separate fuse and the circuit needs to be power at all times from the source because it also supplies power to operate a scan tool at the Data Link Connector, the power outlet in the rear is also a different circuit! I plugged in the fuse tap with the attached wire pointing to my right
(front of truck). I then connected the male connector to the left side of the empty slot #29. (03 and 04 this is not used, 05-06 automatics will have a fuse here for the transmission control module) I chose this because it will have power in accessory AND run. Anybody with an 05-06 automatic that want to do this you will only find a tap with power on in run only - not accessory! right side of #44 or #48 or left side #49.
My TPMS reader can now stay plugged in. It comes on when I turn key to accssory/run and shuts off when I park my truck
-- this picture is after a somewhat longer test drive. Tires were 36 PSI when I pulled out of driveway.
This shows the connections superimposed onto the fusebox diagram
YES the fuse box cover still fits just fine!
WHY didn't I think of doing this before!
Next on the electrical modifications agenda
Make a plug in jumper harness that will switch DRL operation to the fog lights. Its going to require more time and a trip to the pick and pull for a 10 pin connector with wires from a trailblazer so I can make a harness that will just plug in series to our existing harness 10 pin connector -- no splicing of wires and easy to remove.