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Cluster dimming/ flickering on/off on bumps

31 May 2018
Colorado Springs, Co
Hello, looking for some advice on an issue with my 91' coupe cluster. It seems when I hit bumps in the road (not severe) the cluster flicks off and on quickly and dims like a loose connection. After some research I found that the cluster connection on the backside of the cluster could be loose. What makes me think this is not the problem is that I also have a CEL (code 42-02 sensor heater) on and that light stays bright as can be, same as the high beam light. The illuminated Mirror switch also flicks on and off in unison with the cluster. Could this be a fuse or a separate connection besides the connection on the back of the cluster? Voltmeter stays at a solid ~14v
Thanks for any help!
Well the easiest thing to check is too see if the connection is loose. So just remove it and reinstall making sure everything is tight.
Your instrument cluster unit is sending an SOS code that is about to die...
By cluster lights, I am assuming that you mean the lights that illuminate the gauges - called dash lights in the service manual. If so, the dash lights and your mirror switch light (just the light, not the mirror motors) and a whole bunch of other lights get power via the taillight relay and then through fuse #18 .

Get the service manual (there is a link to free versions of the shop manual in the red bar at the top of the Prime web page). In the electrical section of the manual look at the section under the headings dash light brightness control and lighting system. On the wiring diagrams, you should find a list of all the other things that get powered up by the taillight relay. If all of these lights are flickering at the same time, chances are that the tail light relay is failing, or you have a bad connection to the #18 fuse or the relay (check for a burned / loose socket). The tail light relay gets its power on signal from the head light control switch on the steering stalk. It is also possible that the headlight switch is failing / has dirty contacts or that there is a bad connection between the headlight switch and the tail light relay. Finally, there may be a bad connection between the #18 fuse and the dash lights and other stuff.

I would check the relay and fuse first just because it is the easiest to get to. I would then check the operation of the headlight switch because it is the 2nd easiest thing to get to. If all of that checks out good then you likely have a loose connection somewhere. The wiring goes all over the place so you really need the electrical section of the shop manual in order to trace the harness(s) and find all the connectors that are in the wiring path. That involves some serious dumpster diving under the hood and under the dash. Good luck with that - take two aspirin and don't call me in the morning!
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