Description

Peterbilt 320 Wiring Diagram – Factory Schematic for Model 320 (After 1/98)

If you’ve ever chased a short on a Peterbilt 320 using some third-party wiring diagram that turned out to be a redrawn mess, you know the pain. Wasted hours, wrong pinouts, and a cab that still won’t light. That’s why I carry the factory Peterbilt 320 Wiring Diagram in my box. This isn’t a condensed version – it’s the actual 15-page OEM document PACCAR used when the truck left the assembly line. Each sheet matches the harnesses, connectors, and ground points exactly as built. No interpretation, no artistic license.

What This 15-Page Wiring Diagram Covers

Every sheet is labeled “Model 320 Wiring (After 1/98)” and numbered 1 of 17 through 15 of 17 (sheets 16 and 17 exist in the full set but are referenced here for the A/C schematic). The document breaks down the entire electrical system into individual harness views: cab light harness, light bar, bussed electrical center, panel basic harness, cab trailer harness, cab chassis harness, cab engine harness, cab electronic engine harness, and dual-steer-specific harnesses. Page 1 gives you the overall left-hand steer harness layout with cross-references to sheets 4, 6, 7, 8, 9, 11, and 17. That cross-link system is how you trace a circuit from the fuse box to the headlights without guessing.

7 Harness Systems Detailed Across 15 Sheets

You get harness layouts for both left-hand and right-hand steer configurations, plus a dedicated dual-steer layout (sheet 13). The diagram shows every connector (JB1, JB2, JB3), every fuse (Fuse 1, Fuse 2), and the common ground bus that ties all harnesses together. Need the ABS connector location? Look at the body builder pins on sheets 2 and 3. The “INPUT 1 HARNESS” and “INPUT 2 HARNESS” are clearly separated, and the PC board is referenced to sheet 11. For a truck that often gets a dump body or utility box added, this level of detail is what keeps you from backfeeding the ECM.

Read the Notes on Sheet 17 Before You Start

Sheet 17 contains the heater-A/C schematic. If you’re working on a cab that has climate control problems, go there first. The note at the bottom of sheet 1 says: “FOR THE HEATER-A/C SCHEMATIC SEE SHEET 17.” That’s the kind of cross-reference that saves you from pulling the wrong harness apart. Never dive into a wiring job without checking the note block – it’s the first thing I look at when I open any Peterbilt schematic.

Harness Layouts: Left-Hand Steer vs Dual Steer

Two separate layouts are provided. Sheet 1 shows the left-hand steer harness routing, and sheet 3 shows the right-hand steer. But if your 320 is a dual-steer chassis, sheets 10 and 13 are your target. The “Panel Harness Dual Steer” on sheet 10 and “Harness Dual Steer 320” on sheet 13 are unique to that configuration. Combined with the bussed electrical center sheet 7, you can pinpoint where the two steering columns tap into the same power distribution. This is the kind of spec you won’t find in any aftermarket compilation. It’s OEM or it’s wrong.

For reference, the full set also pairs with the Peterbilt 320 Body Builder Manual if you’re wiring a PTO or auxiliary circuit. And if you need operational specs and torque values for the chassis, grab the Peterbilt 320 Operators Manual: Factory Specs & Procedures or the Peterbilt 320 User Manual – 211 Pages of OEM Factory Specs.

Understanding automotive wiring fundamentals helps too – I keep a copy of Automotive Wiring reference handy for gauge and circuit protection basics, but for the 320 you need the exact factory terminals. Another external resource on Automotive Wiring can explain general principles, but never substitute it for these 15 pages.

Is this the complete wiring diagram for all Peterbilt 320 models?

It covers Model 320 after January 1998. Pre-1998 trucks use a different harness layout.

What specific harnesses are shown in the diagram?

All major harnesses: cab light, light bar, bussed electrical center, panel basic, cab trailer, cab chassis, cab engine, cab electronic engine, and dual-steer harnesses. Also includes the heater-A/C schematic on sheet 17, the PC board on sheet 11, and the common ground bus. Each sheet identifies every connector (JB1–JB3, MP2A/MP2B, SR1–SR4) and fuse position. The cross-references are printed directly on the schematics – you follow the arrows to the next sheet. No flipping back and forth through a separate index.

You’ve got a Peterbilt 320 that’s doing something weird with the lights, the trailer circuit, or the body builder interface. Don’t burn a Saturday chasing a WAG. Access the Factory Manual, pull up sheet 1, and trace the harness the way PACCAR intended.