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finding the tach wire

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skywatcher2001 
Member - Posts: 37
Member spacespace
Joined: August 17, 2010
Location: California, United States
Posted: September 27, 2010 at 9:42 PM / IP Logged  
I have a 1999 Chevy Siverado 1500, V8 (4.8L)
I installed a Viper 5701 alarm. Can I tap into the TACH WIRE at the dashboard gauges or must I get it off the PCM?
Pass on what you have learned - Yoda
howie ll 
Pot Metal - Posts: 16,466
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Joined: January 09, 2007
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Posted: September 28, 2010 at 1:03 AM / IP Logged  
Test. The right wire should be tested with a DMM set to AC volts, you should get a reading of 1.5-3.5 VAC at idle increasing slightly when you rev up.
skywatcher2001 
Member - Posts: 37
Member spacespace
Joined: August 17, 2010
Location: California, United States
Posted: September 28, 2010 at 9:39 PM / IP Logged  
yes, I did I believe the tach wire was (is) the problem. The tach wire at the Dashboard Gauge isn't dedicated to just tach. It also supplies other gauges too (abs, fuel, brake, etc).
So I need to go to the PCM. Any idea which pin (wire color) it is??
Pass on what you have learned - Yoda
howie ll 
Pot Metal - Posts: 16,466
Pot Metal spacespace
Joined: January 09, 2007
Location: United Kingdom
Posted: September 29, 2010 at 2:54 AM / IP Logged  
If you have lots of wires going in you're wrong, the wire you described is the IGNITION feed to the guages. If you have a plastic flexible printed circuit board on the rear of the instrument panel there will be 3 terminals behind the rev counter (tachometer).
1 = 12volt ignition.
2 = Ground.
3 = Tach.
Test.
howie ll 
Pot Metal - Posts: 16,466
Pot Metal spacespace
Joined: January 09, 2007
Location: United Kingdom
Posted: September 29, 2010 at 2:55 AM / IP Logged  
Sorry I meant to add that if it is a flexible printed circuit board there will be lots of tracks visible, trace the tracks back to a connector.
skywatcher2001 
Member - Posts: 37
Member spacespace
Joined: August 17, 2010
Location: California, United States
Posted: September 29, 2010 at 11:46 AM / IP Logged  
What I did is cut that wire (white) and the tach went to zero so I figured I had the right one. After I connected the Viper 5701 (and DLPKGM) into the tach the ABS LIGHT, BATTERY and FUEL LIGHTS came on (fuel gauge also registered zero).
I like your idea...to trace the lead on the circuit board. I'll try that.
Pass on what you have learned - Yoda
kreg357 
Platinum - Posts: 7,783
Platinum spaceThis member has made a donation to the12volt.com. Click here for more info.spaceThis member has been recognized as an authority in Electrical Theory. Click here for more info.spaceThis member has been recognized as an authority in Mobile Security and Convenience. Click here for more info.spacespace
Joined: January 30, 2009
Location: Pennsylvania, United States
Posted: September 29, 2010 at 12:00 PM / IP Logged  
The Viper should sync up to a cylinder Ignition Coil just fine.  Might be easier to run the wire into the engine compartment.
Soldering is fun!
skywatcher2001 
Member - Posts: 37
Member spacespace
Joined: August 17, 2010
Location: California, United States
Posted: September 29, 2010 at 12:02 PM / IP Logged  
I did run a wire into the engine compartment. I'm just trying to find the tach wire.
Pass on what you have learned - Yoda
kreg357 
Platinum - Posts: 7,783
Platinum spaceThis member has made a donation to the12volt.com. Click here for more info.spaceThis member has been recognized as an authority in Electrical Theory. Click here for more info.spaceThis member has been recognized as an authority in Mobile Security and Convenience. Click here for more info.spacespace
Joined: January 30, 2009
Location: Pennsylvania, United States
Posted: September 29, 2010 at 1:02 PM / IP Logged  
A Tach signal can be found at ignition coils and fuel injectors.  As Howard pointed out, a Digital Multi Meter is necessary to verify the correct wire.  All connections in the engine compartment should be soldered. 
Soldering is fun!
skywatcher2001 
Member - Posts: 37
Member spacespace
Joined: August 17, 2010
Location: California, United States
Posted: September 29, 2010 at 1:12 PM / IP Logged  
Thanks Kreg,
Im going for the injectors (easy to reach and find). I will solder when finished. thanks for your help.
Pass on what you have learned - Yoda

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