For the past 6 months I've had this issue with my dash lights 'flickering'.
When I'm driving to work in the dark early hours I have my headlights on. After about 10-15 minutes, the dash lights that illuminate the cluster dim to about 75% of their regular brightness and the blue highbeam indicator light comes on about 1/2 of it regular brightness along with both turnsignal lights, both staying on solid also at 1/2 of their normal brightness. If I smack the top of the dash over the cluster it will correct itself for a few minutes to seconds and the repeat the problem. If I hit a bump in the road or go over some railroad tracks it will bring it on or correct it if it's flickering. If I flex the steering wheel up a little it will correct or reproduce the issue. When I do that sometimes, the tach will drop 50% of its RPM of what ever it is running at at the time. I have tried the wiggle wire test behind the cluster with no results. I seems to only happen after the cluster has warmed up. When I drive with the lights out and turn the lights on at dusk, the problem begins immediately. My question is, are there any solder points on the cluster's circuit board that could be breaking down to be re-soldered like a fuel pump relay needs on occassion? Sorry for the long but frustrating post. I really hope someone out there can direct me where to look next.

Thanks.
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'86 sedan with 471,000 miles on the original engine and automatic transmission

The symptoms described matched mine. Dim dash lights, turn signal and high beam indicator glowing in the otherwise darkened dash. Last night, I turned on the lights and reached behind the cluster - somewhat of a tight fit with my arm - and there is some wire or connection loose. I think it might be the 90 degree white connector that slips on to the circuit board - the cluster has been removed so many times and that connection is just a friction fit. I had the car voltage regulator checked last time the car was in the shop, so I knew that was not the problem. So simple - wish I'd done it this way before.

Problem fixed. This morning driving in, the issue was worse than ever and driving me NUTS, NUTS, NUTS..... When I got to work, I had about 20 minutes before I had to clock in, so I broke out my phillips screwdriver and went to town on the cluster. Reached behind it and wiggled everything only to find the 1/2 moon plug loose. Pushed it in an lo and behold.....no more flickering.
Sweet. Thanks for the direction guys.
My sanity saved by the Brickboard once again.
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'86 sedan with 471,000 miles on the original engine and automatic transmission

Never had this issue But if I was to guess, I would resolder the Large Pins that the Half moon and larger connector go into If you even get at them from teh Soldered side.. They take a bit of stress having those buly connectors plugged into them.
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'75 Jeep CJ5 345Hp ChevyPwrd, two motorcycles, '85 Pickup: The '89 Volvo is the newest vehicle I own. it wasn't Volvos safety , it was Longevity that sold me http://home.lyse.net/brox/TonyPage4.html http://cleanflametrap.com/tony/

I think it's probably just one of the main harness connectors to the dash cluster that has worked itself loose. Pull the dash enough to re-seat all the plug wires and see if that does the trick for you.