Where is the ALDL connector on your GM truck (1988–1995)?
The ALDL connector is the door into your truck's computer. Without it you can't read codes or live data. Nearly every GM of these years has one, and you can find it in minutes.
Where to look
On TBI-injected S10, Sonoma, Blazer, Jimmy, C/K and Sierra trucks it is under the dash on the driver's side: look above your knees, near the steering column or behind the fuse panel cover. It's usually a rectangular 12-hole connector in two rows (six on top, six on the bottom), sometimes with a plastic cap.
If you can't see it, feel under the dash: on some models it sits behind a small panel or is taped to the harness.
Which terminals matter
| Terminal | Purpose |
|---|---|
| A | Ground |
| B | Diagnostic terminal (jumper it to A and the Check Engine light flashes the codes) |
| E | Serial data at 160 baud: live data comes from here (some models use M) |
| G | Carries 12 V from the fuel pump circuit: never connect a data signal there |
What if mine has no pin E?
Some 1991-and-later trucks use a different protocol (8192 baud on pin M) and can't be read the same way as 160-baud trucks. Confirm model, year and engine before buying anything.
Next step
With the connector located you can read trouble codes with a jumper wire, no scanner needed, or see live data with a WiFi scanner.
Want to see this data on your phone?
The RT-Web scanner reads your 1988–1995 GM truck's computer over WiFi, no apps and no internet.
See the scanner Ask on WhatsApp