not sure if it belongs here, but for those of you with air/fuel ratio gauges in an '04 f150, how do you have it hooked up to opperate.thanks.

 

there are 3 or 4 wires on your o2 sensor. Probe them until you find the one that fluctuates voltage between 0 and .9 volts . hook the gauge up to this wire. one of the others will be grounded and another will be 5v, dont use them.

 

Rather then the hunt and peck method ( without evening knowing the wire count ) the 2006 EVTM for the Engine controls - 5.4L ( cell 24 )

HO2S11
Gray w/ Red stripe : Signal Return to the PCM
Gray w/ Light Blue stripe : Signal from PCM to heater element ( thermristor ) PCM Pin # 29
Red w/ Yellow stripe : Circuit 391 from Fuse F32 15 A Hot in Start or Run positon
Red w/ White Stripe : Signal to PCM adjusted from Circuit 391 -> Pin 69 on PCM harness Noted as HTR11

HO2S21
Gray w/ Red Stripe : Signal Return to the PCM
Red w/ Black Stripe : Signal from PCM to heater element ( thermristor ) PCM Pin # 28
Red w/ Yellow Stripe : Circuit 391 from Fuse F32 15 A Hot in Start or Run positon
Yellow w/ Light Blue Stripe : Signal to PCM adjusted from Circuit 391 -> Pin 70 on PCM harness Noted as HTR21

From what I can tell from the EVTM ( did not install a A/F ratio gauge in my '06, had one in my '01 while messing with tunes and intakes ) you want to tap the Gray w/ Light Blue on HO2S11 or Red w/ Black Stripe on HO2S21.

This needs to be verified on your 2004 MY, to make sure it is not different from the 2006 EVTM ( should not be different, but best to check ) and verify that I am reading the diagrams, so meter the pin at the PCM, once the engine has been through at least one drive cycle ( steady throttle over 48 MPH )

Taking a quick look, it seems to can get to these in the engine compartment, if you don't feel like crawling under the truck to gain access.

Good luck, let us know how it turns out.