2002 Mustang GT, Viper V790xv

Printed From: the12volt.com
Forum Name: Car Security and Convenience
Forum Discription: Car Alarms, Keyless Entries, Remote Starters, Immobilizer Bypasses, Sensors, Door Locks, Window Modules, Heated Mirrors, Heated Seats, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=6692
Printed Date: September 01, 2025 at 9:59 PM

Topic: 2002 Mustang GT, Viper V790xv

Posted By: rrspyder
Subject: 2002 Mustang GT, Viper V790xv
Date Posted: December 14, 2002 at 5:28 PM

Hello everyone-

Got a tachometer question for my 2002 Mustang GT. The Viper V790xv manual states the tachometer can be located at a coil pack and will be around 3-6V AC. The wire color chart I am using says I can find it at the PCM as lt GREEN / WHITE. However when the engine is running my voltometer says the voltage is 30.2-30.4V AC. Any ideas on what I am doing wrong? Also, woud you recommend pulling it from the wire running to PCM or just off of a coil pack. I ask because I think it would be easier to run a wire through the firewall to a pack then all the way over to the passenger side to hit the lt GREEN / WHITE wire at PCM. I also tested out a wire off of another pack and it had the same voltage however still not the voltage that the manual states.

Any ideas greatly appreciated.

Thanks,

Kyle

Replies:

Posted By: Velocity Motors
Date Posted: December 14, 2002 at 5:49 PM

For the 3.8L motor, use the dk. blue/lt. green, RED / lt. blue, or the pink/white. All of these wires are found at the coil pack.
The 4.6L motor uses a separate coil for each cylinder. Go to any coil and use the wire that is NOT red or WHITE/ lt. blue.
Make sure that you have the RED lead on the DMM on a 12 volt + and the BLACK lead on the target wire.

-------------
Jeff
Velocity Custom Home Theater
Mobile Audio/Video Specialist
Morden, Manitoba CANADA

Posted By: rrspyder
Date Posted: December 15, 2002 at 6:32 AM

Thanks for the reply.

I am pretty sure I have the right wire for the tachometer per your instructions however the voltage question concerns me. Your reply says to have RED Lead to 12+ and Black to target. However I think the Viper instructions state it the other way around. I'll read them again.

I just don't want to hook the wrong wire that has higher voltage than the unit is expecting and blow it up or something :)

Thanks,

Kyle

Posted By: JWorm
Date Posted: December 15, 2002 at 3:45 PM

Hooking up the wrong wire won't cause a problem...the 790 just won't learn tach and won't start. I have a cheap meter that I bought at Sears a few year back that will give me readings of about 29 or 30 volts if I try to test a tach wire. If I take a good quality meter and hook it up the same way the reading will be in the typical 2 - 6 volt range.

Posted By: rrspyder
Date Posted: December 15, 2002 at 6:02 PM

That could very well be my problem than cause mine is the cheap sears one.

Thanks for the help,

Kyle K

Posted By: themagicone
Date Posted: December 16, 2002 at 10:24 AM

the problem is the range on your dmm, if you can change it go to 0.00 and try it.