Signal help, Tach and speed

OutToWinPAHC

New member
I picked up a Blitz SBC-I-color boost controller off of a friend. I am looking through the manual so I can prep the install and some of the extra features require the use of a tach signal, and speed signal. I was wondering where I can grab the tach signal from without pulling the cluster. I assume it comes from the ECU or from the power transistor circuit.

The other thing is speedo is a digital signal, usually this happens on most cars VSS to cluster (analog) then the cluster converts and sends signal to the ECU or other computers in a digital signal. I was wondering if the ST185 does this?
 

CSAlltrac

New member
One of the dizzy harness plug wires should be a tach. signal, forgot what one it is. ST185s have a cable driven speedo. The cable does have a plug going to it so I would imagine one of them is a pulse signal you can grab.
 

l0ch0w

New member
This is an easy one actually... you dont have to tear up your dash to find it. Youve got a few nice places in your harness to tap in. One is at the A/C amplifier connector, and the other is in the IG1/IG2 cable connector coming in from the engine harness. For pinout locations, or a neato patch harness, PM me. In the engine bay you would tap into the black wire coming into the Igniter.

The above advice is incorrect. DO NOT tap into the dizzy harness, those are trigger signals only. In particular you are interested in the Tach signal that comes from the igniter.

The Tach signal in the alltrac is a bit different than most though. Instead of a 12v square wave its a 20v square wave. Just be sure that your unit can handle the extra voltage...
 

OutToWinPAHC

New member
I have to check the voltage with the manual, but the manual speed sensor goes to the cluster which also outputs a digital speed signal, this goes from the cluster to the cruise control ECU. I can splice into this and use it for the blitz unit.

CruiseControl1.jpg
 

l0ch0w

New member
That speed sensor is not in the gauge cluster. If you have a look at where the speedo cable leaves the transmission you will see the sensor and a wiring pigtail coming off of it... So you can either tap into it under hood, or off the IG1/IG2 connector in dash where it comes in from the engine bay.
 
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