Dim Speedo

Topic: Dim Speedo (Read 969 times) previous topic - next topic

Dim Speedo

April 03, 2014, 06:06:07 AM

Hi all. Have an 88 Tbird coupe 6cyl, and the lcd speedo is quite bright when I first start the car, however sometimes dims as I drive. Occasionally, it goes so black it can't be read. I am assuming a bad earth somewhere that gets a bit warm the longer it's active. I don't have a wiring diagram, so any suggestions where I should look for this bad earth? Behind the instrument panel? On the firewall somewhere (inside or out?)? Or in the engine bay?

Any suggestions may save me dismantling something unnecessarily. Or any suggestion as to another cause would also be very welcome.

Cheers

Merv

Dim Speedo

Reply #1 – April 03, 2014, 05:34:58 PM

The ground (Earth) connection is behind the dash. Several incandescent lights share the same ground.

With the car's exterior lights on, the Cluster Illumination Relay is energized. With the relay energized, the LEDs are powered through the headlight switch and the dimmer control.

With the exterior lights off, the LEDs are powered through the ignition switch in ACCY or RUN.

Dim Speedo

Reply #2 – April 03, 2014, 05:41:54 PM

When the LEDs go dim, try reversing the status of the headlight switch. If this brings the LEDS back to bright it will help pinpoint the problem.

Dim Speedo

Reply #3 – April 03, 2014, 06:31:02 PM

Thanks so much for this reply. Ordered a full shop manual from Auto Lit two weeks ago, only to be told yesterday they had sold it elsewhere, so starting my search for a manual again. Your scans will get me started while waiting.

I have since read about a recall on the ignition switch, and no idea if mine was replaced. Did find the key unusually warm when removed from switch on my first long drive, so perhaps it may also be the problems cause. Do you know of a supplier of new switches?

Again, thanks for the good reply.

Merv

Dim Speedo

Reply #4 – April 03, 2014, 07:37:02 PM

Try rolling your dash light dimmer by the headlight switch back and forth a few times as well. These dimmer switches use a coil of wire with a moving contact, and that contact goes bad after time. If wiggling or moving the dimer makes your lights flicker this might be your problem. They will obviously get brighter and dimmer as you move the wheel, as that is what the wheel is for, but the transition should be smooth in relation to wheel movement - there should be no sudden changes in brightness.