I'm going to wire in an aftermarket gauge into the factory position, I would like to know which wires from which connector(s) I'll need.

I'm going to splice into the wiring for the tach somewhere behind the connector(s) in case I want to revert to the stock one later on.

keep in mind this aftermarket tach is going in place of the stock one, and I will not be running two tachs.

I do not want a bulky tach pudging out and disrupting the look of the interior, which is why I want to put it in place of the original.

I just got done filming a video on installing an aftermarket Heads Up Display in a Fiero which also included a tach display. If only the video were finished editing it would have been something to check out. I'm not at home at the moment to check but I believe if you removes the rear trim from the gauge cluster you'll see a connector plugged in directly behind the tach location. You'll want to locate a solid white wire. I can get you the pin location when I get home if no one else chimes in beforehand. That white wire is the tach pulse wire. You can also tap any pink with a black stripe wire as your ignition switchable power wire.

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87 Fiero GT 3.4 Pushrod with 7730 ECM & DIS
88 MERA #8013
85 Fiero SE with 3.1 pushrod
86 Fiero SE 2.8 stock
http://www.youtube.com/LostNotForgotton

What does the transmission have to do with the Tach reading?

Oops sorry. I must have been multitasking at work. I didn't mean to say transmission. The speedometer is the one read through the transmission. We're you able to locate the wire you needed. If not I can pop off the trim panel and give you the pin location or take a pic of it?