Instrument backlights not working correctly

[Fox2newedge]

Hello everyone! If I'm posting in the wrong place, please let me know.

I have a 2002 GT that when the headlights are turned on, only the needles on the gauges illuminate. The numbers/tick marks do not illuminate. The headlight dimmer works, meaning the instrument needles, a/c backlighting and stereo will dim or brighten as they are supposed to. I've checked the fuses and don't see any burned out. Has anyone ever seen or heard of this before?

Thank you in advance for any help!

 

[Mustang5L5]

The backlighting is physical bulbs. I'd start by pulling the cluster and checking to see if the bulbs with by using a 9V battery and test leads.

Now would be a good time to upgrade the bulbs to LED's as well.

 

[rednotch]

And test the bulbs before you bolt it back together they are polarity sensitive... So won't light if installed backwards.

 

[Pinellas50]

The bulbs don't illuminate the needles as well? If not, how are they lit?

 

[Mustang5L5]

reflection. There are 5 bulbs that do the guages and needles. Depending on which one is on it can make the illumination uneven.

Of course this is assuming these are factory guage faces and nothing aftermarket

 

[Pinellas50]

Please update on what you find Fox2.

I have the opposite of you where all the guages are illuminated fine but all of the needles are not. My car already had LED bulbs in the cluster when I bought it.

 

[Fox2newedge]

Good evening everyone! I wanted to post an update as to what I have found. I checked all of the fuses before even getting to this point, and they are all good. I pulled the cluster, which are factory gauges, and checked the bulbs. All of the bulbs are good.

After looking closely, it seems the bulbs illuminate the numbers using a "fiber optic" effect through clear plastic veins. The needles however, are illuminated from within their own housing (a small metal cup). Looking at the circuit board on the back of the cluster, I can't see any burned traces.

I swapped in a different cluster and it does the same thing, which tells me the problem is in the car's wiring. I changed the headlight switch in case it was a bad dimmer, but still the same results.

At this point, I was hoping someone had a wiring diagram for an '02 GT dash (or instruments) so that I can figure out which pin powers the light bulb circuit for the numbers on the cluster. Worst case scenario... if I can't locate the problem, I can jump power to that pin once I find it. The dimmer may not work that way, but at least they will be illuminated.

Thank you again in advance for any help.