The other item to check BEFORE you crawl under the car (looking for the ellusive reason why your tach doesn't work) is the OPR. The overvoltage protection relay is the item mentioned by lietuviai. Its behind the lower right hand dash panel under the glove compartment.

You don't need to pull the glove compartment, PULL the lower panel. The relay comes right out and there is a red 10amp modern style fuse that protects the EGR computer. The OPR provides power to the the EGR computer and the EGR computer supplies the signal to your tach from the tach sensor. I just got my car back from the body shop and the OPR relay fuse was blown as was the radio fuse.

Makes you wonder WTF they were doing to blow two fuses. At least the fuses did their job!

This would be on a 1984 or 1985 617 Turbo.

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84 300DT Puke Yellow. Totalled after 438,000
84 300DT Orient Red. 169,000 (actual mileage may vary)
2002 Explorer EB (wife's)

I don't think I need the EGR computer anymore since my EGR has mysteriously vanished.

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DJ


84 300D Turbodiesel 190K with 4 speed manual sold in 03/2012

My tack wasn't working either. I had read somewhere to place a small piece of foam or something that would press down again the silicone layer of the tack (garbage can) part and then screw the cap down to put pressure , Mine started working after this.

85's have a different style.....

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Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John