I did gauges on my 03 LB7 over the weekend.

I got the autometer Sport Comp II gauges. Boost and pyrometer.

They both work fine with the lights off. But when I turn the lights on the pyro finds a "happy place" and stays there.

I have both gauges wired to the same place. The Pyro power is ran to a 12V keyed source, and I ran the LED power to a switched source that is controlled by the dimmer switch. The dimmer does work to dim the gauges, but when the lights are on, the pyro will just stick at a certain temp and wont move.

Any suggestions?

Sounds as if the pyro is on a varied voltage?? A cheaper DMM (digital multi meter) would tell you if there is 12 Vdc there.

Sounds as if the pyro is on a varied voltage?? A cheaper DMM (digital multi meter) would tell you if there is 12 Vdc there.


I have a meter. The pyro power is a good 12 volts with the key on (11.82VDC actually).

When I turn the headlights on, the pyro and boost gauge lights come on, but they are wired to the variable power source from the instrument cluster dimmer knob (something close to 0VDC with the dimmer switch at the bottom) and 12VDC with the instrument cluster lighting at full intensity.

But no matter where I have the instrument cluster dimmer knob at, with the headlights on, the pyro does not move.

I had a similar issue a couple of trucks ago...it appears the pyrometer signal is a little more sensitive than I anticipated. I ended up re-routing my switched power lead as far away from the lead for the gauge lights since, apparently, the dimmer created enough electrical interference/feedback to disrupt the pyrometer signal. I also now use the light/dimmer terminal pin in the sub panel by the footboard (where the trailer brake controller harness plugs into). The pin array to the right of the trailer brake terminal has a light/dimmer pin (bottom right). Using that for the gauge lights and dimmer seems to have fixed my interference problems with the pyrometer signal.

try moving the grounds for the light and the guage function to seperate grounding points. I haven't had any issue with my autometer z series but I have read of some people having erratic indications that turned out to be grounding problems. I picked up my switched power and light dimmer circuit from the mbec panel by your left foot as vin63 did.

try moving the grounds for the light and the guage function to seperate grounding points. I haven't had any issue with my autometer z series but I have read of some people having erratic indications that turned out to be grounding problems. I picked up my switched power and light dimmer circuit from the mbec panel by your left foot as vin63 did.

I used one of the ground straps in the engine bay on the firewall and it all works great now.

I had a similar issue a couple of trucks ago...it appears the pyrometer signal is a little more sensitive than I anticipated. I ended up re-routing my switched power lead as far away from the lead for the gauge lights since, apparently, the dimmer created enough electrical interference/feedback to disrupt the pyrometer signal. I also now use the light/dimmer terminal pin in the sub panel by the footboard (where the trailer brake controller harness plugs into). The pin array to the right of the trailer brake terminal has a light/dimmer pin (bottom right). Using that for the gauge lights and dimmer seems to have fixed my interference problems with the pyrometer signal.

My CB radio messed up my Trans Temp on the old Ford and EGT on the GMC.

I just installed new ISSPRO gauges and will check the CB this weekend to see if it messes with the signal.

You are on to something with Vin63 post.