tach wire 1990 lexus ls400

I have installed remote starters in a couple of vehicles, so I do have a basic understanding.

In a 1990 Lexus LS400, do I have to run a wire through the firewall into the engine compartment to get the tach signal, or is there an in-cabin source?

If a wire is needed through the firewall, any suggestions on where to go through in the LS400, since they made these things sound-tight?

This will be a DEI Viper 160xv.

TACH SIGNAL

Black

At test plug on front of engine

AC

Or @ the igniter behind the pass. headlamp assebly, and air flow meter box.... same color

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Thanks for the reply--I did see that info on the wiring info sheet, but is there not an in-cabin signal that can be used?

If going through firewall is necessary, is there a recommeded method of running wire through?

Well when you take the thing apart just look around and if you dont see a factory rubber grommet or wiring location, carefully drill a hole where you are certain there is nothing on the other side

passenger side. theres a nice big rubber grommet there. since you should be running a wire for the hoodpin under the hood anyways, you can just run the tach wire with it. i usually just use a long fish, like an old antenna with a sharpened tip to push through a factory rubber grommet. its easier to move it around things and since it is much smaller, less of a chance of damaging things you can't see on the other side. onces it's through, tape the wires tightly and then just use a little grease or WD40 where you taped them to help make it slide throught like butter. 95% of cars have many grommets to use, although when you do have to dirll or punch a hole, make you you seal it after with something so water doensn't leak inside.