84TD,
Not trying to discourage you, but I stared at a 73-79 F-Series, 73-91 E-Series cluster for 10's of thousands of miles. I am not sure where you would graft in a tach.... The instrument cluster, is broken into 3 sections. The left section, has the oil pressure gauge at the top, the left turn signal indicator, and the BRAKE light in the middle, and the fuel gauge on the lower right. The middle section is the speedometer, and the bright light indicator and the odometer, the speedometer takes up the entire middle section, and the right section has the ammeter at the top right, the right turn signal indicator, and another warning light in the middle, and the coolant temperature gauge in the lower right. It has been a few years since I drove on, so this is all from memory...
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http://www.youtube.com/watch?v=_0dJxuH7Xas
Looking at the pictures and the beginning of Jon's video, I am not sure where to graft one in. To place it in either side section, you would have relocate a turn signal indicator, the middle, relocate the speedometer. I have seen an aftermarket tach in a "mounting can" mounted to the steering column and it blocked most of the speedometer. I have been thinking about this since someone said something about putting one in a van either Compudock, or IDIDieselJon (Jon in Canada with the IDI motorhome) and not thought of a good solution. The only thing that may work, is use one of the digital readouts, like the one that several have used for a Pyro... I know Wonderer-rocc used in his van with this same dash.... he installed it in the dash, to the right of the radio, in the panel between there and passenger dash....., not the best place when you are wanting to see it easily..... I know on the panel to the left of the cluster, has the wiper controls, the A/C Vent, the area with an area for warning indicators, In a gasser an Emissions warning, In a diesel, probally the WIF, and WTS lights (Have not driven a diesel pre-91 van) and the headlight switch. On the 73-91 dash, the dash space between the drivers door, and the radio/HVAC area has been utilized. The switch for the dual tanks, placed in the bottom of the dash, seems like a "just put it somewhere, there is no good place to put it"
The 92 and later dash is a bit better... but still busy... it reminds me more of the OBS Style dash in the trucks.... may be easier on those... but not sure. I don't remember seeing a tach as an option in any van, in the trucks of any era, but not the vans..... I wish you all the luck, and maybe someone with a better imagination can see a solution that I can not see......
