Hi,

Dashboard illumination in my 1990 Honda Civic Si 2-door hatchback has
failed.

The transmission range indicator still works; "2", "D3", "D4" and etc.
appear in green. Speedometer, tachometer, fuel gauge & etc. are dark.

The Honda Civic 1984 thru 1991 Haynes Repair Manual, page 12-17 shows
"Dash Light Brightness Controller" and one bulb symbol annotated
"Gauge Illumination (3.4W X 1.4W X3) ... Cigarette Lighter Illumination (1.4W)".

Appears multiple bulbs are involved. They wouldn't all fail
simultaneously. The failure is probably in the brightness control?

I haven't found instructions to reach the back of the brightness
control and the bulbs. Is removal of the instrument cluster
necessary? Can the bulbs be replaced without removing the instrument
cluster?

Thanks, ... P.

A few things:
a) Once upon a time, we had a 1999 Saab 95 where many panel lights failed and we thought the same thing. As we had it fixed under the factory warranty, we asked the service manager what he thought. He stated that as the lamps age, they start to fail, and when they fail, they tend to do so as a group - especially if they are typically left at the brightest setting. He also stated that a mild power spike possible by turning off headlights or some other load drop could exacerbate the issue. So, do not dismiss straightforward lamp failure.
b) Yes, it could well be the control that is bad - but that can be tested before replacement.
c) And, you have surely checked any fuses and such?
e) And you understand that the transmission indicator is separate from the instrument lighting?
f) And, yes, you must remove the instrument cluster to replace the lighting..

> Appears multiple bulbs are involved. They wouldn't all fail
> simultaneously. The failure is probably in the brightness control?

See above. Assume nothing. That is how you get into trouble. Avoid the fallacy of "Post hoc, ergo propter hoc".

Now, you once posted here on the ignition for your Honda, and spun many wheels because of an entirely unsystematic approach to the problem. Let's try to avoid that this time.

https://www.ebay.com/itm/113771048202? Is a link to a lighting control for your vehicle. I advise testing your existing unit prior to purchase, however. This is possible without heroic measures.

https://www.youtube.com/watch?v=sIToQfMjh-U Here is a decent YouTube on how to remove the instrument cluster, the lighting control and how to replace the various lamps. As you will have to remove the cluster to do anything at all, I suggest you obtain the LED kit and do it anyway, whether a dimmer is required or not.

So, pick a clear, dry day. Get all the tools necessary together in one place. Get several cheap plastic containers with lids and a Sharpie. Have your cell-phone camera ready. Have a VOM ready. I would suggest you have a few small alligator-clip jumpers available as well for testing the control. I believe it has only three leads - so, again, a simple process.
a) Take pictures every step of the way.
b) as you remove screws or parts, put them in a container, and label the what-goes-where with the Sharpie.
c) Take your time.
d) Start with the control. When you free the control, use the VOM to see if it is functional. Your manual should have a wiring diagram, so follow that for continuity and dimming properties. When in doubt, replace it. If the control tests bad, purchase a new one before going any further.
e) When you free the instrument panel, replace the incandescent lamps with the LED.
f) Put everything back together, and enjoy.

Figure that if you start after breakfast, you should be done by lunchtime, excepting having to purchase the dimmer if needed.

Peter Wieck
Melrose Park, PA