ALDL Signal Ground wire/ Where does it come from?

For any that looked at my other post i am rewiring my ALDL conector.
I got all the infor i need exsept where to tap into the signal ground wire.

Would also like to know what this wire does...

Clarify what OBD type you are and what number of pins are on the DLC you are wiring up. With your mods, it's a bit difficult to know for sure what you have...

it a 93 car with a 97 OBDII computer, engine harness and the ALDL out of my 97 (the 16 pin one). The dashboard or internal harness is the orginal one out of the 93. I have done several splices to get the two to work together.
Gawd i wish i knew about all the difrences when i bout the 93 roller:cry:

After alot of freaking reading and search on google it looks like the signal ground comes from D1 of the PCM, now where that is under the dash im not sure. Im going to tap into it right at the PCM.

I don't even see that the 16 pin OBD-II DLC uses a "signal ground". What pin on the DLC are you trying to wire it to?

Pin #5 on the ALDL

http://autotap.com/faq.asp it shows it about 2 pages down.

You know it might make sense that the tech guy at autotap are wrong HOLD ON why doesnt it show the serial data wire in pin #9 on that site?

Did i f***ing get the OBDI and OBDII ALDL wiring mixed up :mad:

Shoebox, Where does the serial data (the light brown wire) go in the ALDL conector for a 97 OBDII?

96 and above OBDII conector

Pin 2 - J1850 Bus+
Pin 4 - Chassis Ground
Pin 5 - Signal Ground
Pin 6 - CAN High (J-2284)
Pin 7 - ISO 9141-2 K Line
Pin 10 - J1850 Bus
Pin 14 - CAN Low (J-2284)
Pin 15 - ISO 9141-2 L Line
Pin 16 - Battery Power


The Three Flavors of OBD II

While the parameters, or readings, required by OBD II regulations are uniform, the auto manufacturers had some latitude in the communications protocol they used to transmit those readings to scanners. Naturally, each felt they had the one true way, so we have three different OBD II communications protocols in use.


What Communications Protocol does my vehicle use?

As a rule of thumb, GM cars and light trucks use SAE J1850 VPW (Variable Pulse Width Modulation). Chrysler products and all European and most Asian imports use ISO 9141 circuitry. Fords use SAE J1850 PWM (Pulse Width Modulation) communication patterns.

There are some variations among captive imports such as the Cadillac Catera, a German Opel derivative, which uses the European ISO 9141 protocol. If you have first hand knowledge of other such variations, please send them in and, together, we can build a more complete listing.

On 1996 and later vehicles, you can tell which protocol is used by examining the OBD II connector:

J1850 VPW--The connector should have metallic contacts in pins 2, 4, 5, and 16, but not 10.


From this it looks like the serial data wire should go to Pin# 2