While this is for a 1990 LS400, I think it applies to most Lexus applications.

I will be doing a DEI Viper 160XV install, and the wiring info for the LS4 states that the tach signal is a black wire near passenger headlight.

Is there an in-cabin signal that can be used for the tach signal so that I don't have to run a wire through the firewall?

If not, is there a preferred method of running wire through the firewall in our hyper sound-deadened Lexuses?

 

Surely somebody has done this...

 

I'm guessing you got that wire color from DEI's wiring info? I have access to 2 other programs at work, and I can look and see if someone lists something different. With DEI you can always use voltage sensing too.

 

you can disable the tach sensing if you really want.

it is not needed i'd guess... only time it is useful is when som1 is reving on the engine.. it'll sense it.. and then kill the power.

 

I thought tach sensing was for startup--to engage starter long enough to actually start (i.e. longer in colder weather)--I don't think it has anything to do with killing the engine--that's what the brake wire is for.

 

Actually I got the tach wire info from 12volt forums as well as Bulldog's website (I have installed a couple of Bulldog remote starters in the past, but no more!)

I would love to see what DEI's wiring info gives, if you have access to it.

Also, does voltage sensing mode allow for longer cranks when cold (i.e. it senses when the engine has actually started) without using tach wire at all?

 

Just so everyone is clear, tach sensing is indeed used to stop cranking the car when starting up, and on some remote starters, it is also used as a shut off if the car revs itself too high it will shut off. I don't actually put in DEI starters anymore because they are too much of a headache and have a lot of issues, so I don't know about cranking longer in cold weather. I will tell you this though, voltage sensing is not recommended in colder weather, you should use tach sensing. I was busy today at work, and forgot to look for the other wiring info.

I forgot to mention that DEI's wiring info gave the same exact tach wire as you posted.

 

Thanks for the advice...now I'm intrugued:
What kind of problems were the DEI systems giving you?
What brand remote starters would you recommend?

This advice would GREATLY be appreciated.

 

Its just that the majority of the come backs we get are DEI products, but they're usually older ones. I would recommend either Astrostart or Compustar. In my opinion, those 2 brands are the most reliable out there.

I looked on Wire Magic, Astroflex, and DEI wiring info today at work, and all 3 said the same tach wire for the 90 LS400, so it looks like you'll be going through the firewall.

 

Troy--thanks for the great info.

 

I'm trying to look for this cable myself now. Is it Behind th eheadlight? I'm gonna try taking out the headlight to see if I can find it..

 

Allright well I took my passenger headlight out and I'm not seeing this black cable I need... Can anyone help?

 

Suneet--no need to remove headlight. The ignitor is located just behind (aft) of the headlight under a black box. I think 10mm bolts to remove box. There are 2 ignitors which look nearly identical. The one you're after is the 1st one you have access to. It should have 4 or 5 wires, and i believe the 2nd one in is a solid black one. This is the TAC wire.

 

Just remembered--the ignitors are silver metallic boxes that look kind of like heat sinks (underneath that plastic access panel).

 

To answer the question of handling door lock/unlock functionality:

The door lock/unlock, factory alarm arm/disarm are *not* the same colors as represented in EVERY alarm/remote start install guide. I had to probe with a 12v test light into that mess of 3 wiring harnesses that come in from the driver's door into the footwell. They are ALL negative triggered. Unfortunately I did not document which ones were correct, since I was so frustrated by that point and was running out of time. My apologies for not documenting them. They are, however, very easy to find with a 12V test probe light (with a needle-style probe that will punch into the wire without the need for stripping insulation away).

One tip for finding factory arm/disarm: I spent a ton of time trying to locate the negative triggered wires by pressing lock/unlock on the driver's door. This worked fine in a Cressida I had done a remote start install on previously. However, the 1st GEN LS gets its trigger not from the door lock button, but from the driver's side KEY. So use the key open/close to find the appropriate factory arm/disarm.

The trunk pop is straightforward, as you will just tap into the trunk release switch which is by the driver's knee.

I only did remote start, and not alarm, so I didn't wire in a siren. I ran the tach wire in through the famous driver's side grommet, since breaching the firewall is next to impossible.

Hope this helps--and keep asking questions if I can clarify anything for you.