Funky grounding issue
 

Hey all, quick question for anybody who might be "in the know" about this, since I can't figure out where the issue is coming from.

The problem is relatively simple: my tachometer reads about 500rpms too low due to a poor ground. This is proven to me by the fact that whenever I honk my horn (I live in New Jersey, this happens often), the tach spikes upwards until the horn is released.

My question? Anybody have a clue where the tach / horn grounds to? I hope it's under the hood, or in a (relatively) accessible place, because if it's behind the dash or cluster, it'll be an utter pain to repair.

Schematics call out G102 for the horn and EGR stating it is "BEHIND CENTER OF INSTRUMENT CLUSTER". This is a major grounding point, and if the tach connection and horn connection are affected, then almost everything in the car would be flakey. The tach signal comes from the EGR and is also connected to the 'Compressor/Kickdown Cutout Control Unit". If you don't find a bad ground you might check those or the Overvoltage Protection Relay which feeds power to the EGR.

Most other things don't seem to be affected, really. But it makes sense that the ground point may have been screwed up. I replaced the speedo cable about 5 months back, which is exactly when these issues started popping up. Looks like the ground may have gotten dislodged.

Guess I'll be screwing around behind there, later.