Description

Ferrari 328 GTB, 328 GTS 1989 Wiring Diagram

I’ve seen more aftermarket wiring diagrams than I care to count. They all look pretty until you tap into a fuel injector wire and the color code doesn’t match what’s actually in the harness. For a 1989 Ferrari 328 GTB or 328 GTS, that kind of mistake can fry an ECU or cost you a weekend of chasing ghosts. This is the factory document – printed by Ferrari Servizio Assistenza Tecnica, pulled straight from the original Italian/English/French file. 34 pages of nothing but the circuits that matter.

Fuses and Relays: The Backbone of Electrical Diagnostics

Page 4 of the manual lists every fuse in the right and left junction boxes. You get amperage ratings like A25, A15, A20, and A7.5 – all assigned to specific circuits: headlamp motors, heater fans, condensers, wipers, horns, injectors. The relay callouts match the factory layout. If the AC fan on a 328 GTS stops blowing, you don’t need to guess which relay it is. It’s in the diagram. The index at the front points you straight to “Fuses” and “Relays”. No flipping through 50 pages to find the main box.

Cable Colors – Why the Manual Matters

The “Cable Colors” section (listed as “Colorazione cavi” in the original) is a separate chapter that maps every wire by its Italian color code. Ferrari didn’t use standard Bosch colors for everything. If you’re repairing a 1989 328 GTB and the wiring has been butchered by a previous owner, you need this map to trace circuits without using a multimeter on every pin. The manual gives you the code – not a generic “red/white” approximation.

Fig. 2 – Fuel Injection System

Page 8 shows the injection wiring (Fig. 2 – Impianto di iniezione). The Bosch KE-Jetronic on these cars is sensitive to voltage drops and ground points. One bad connection at the injector driver and the car runs lean. The factory schematic shows exactly where the power feed comes from, what color wire goes to each injector, and how the cold-start circuit is routed. If you’re doing a full harness refresh on a 328 GTS, this figure alone is worth the access.

Fig. 9 – ABS System: Factory Procedure

Page 30 covers the ABS system (Fig. 9 – Impianto ABS). These early Bosch ABS units fail when wiring gets corroded. The diagram includes the wheel speed sensor circuits, the ECU pinout, and the hydraulic unit connections. Without this, you’re pulling codes blind. The aftermarket diagrams I’ve seen for 1989 Ferrari ABS are missing half the sensor shield grounds. This one has them all.

8 Systems Covered in 34 Pages

The manual doesn’t stop at injection and ABS. It walks through the starter and alternator (Fig. 1), ignition (Fig. 3), wipers and washers (Fig. 4), instrument cluster (Fig. 5), lights (Fig. 6), radio, windows, door locks, interior lights, and cigar lighter (Fig. 7), and the HVAC system (Fig. 8). Every figure is labeled in Italian, English, and French – so if you work in a bilingual shop, the terminology is consistent. No misinterpretation of component names.

If you’re a home garage enthusiast who owns a 328 GTB and wants to fix the intermittent wiper or a dead power window, this is the document that keeps you from cutting the wrong wire. For professional technicians, it’s the difference between a one-hour diagnosis and an all-afternoon headache. Pair it with the Ferrari 328 GTB & 328 GTS Technical Specifications Manual for torque specs and fluid capacities. Need a manual for a later model? Check the Ferrari 575 GTC 2004 User Manual – Factory Setup Guide for Bosch Motronic wiring. Working on a classic? The Ferrari Testarossa Workshop Manual – 557 Pages of OEM Specs covers the flat-12 systems. For a broader understanding of electrical theory, read the Automotive Wiring article on Wikipedia. And if you want context on how these systems fit into the Automotive Industry Overview, that page covers the evolution of electronic diagnostics.

Why a Factory Scan Beats Aftermarket

This is a direct scan of the original Ferrari publication, not a redrawn or translated copy. The cable colors come straight from the Italian factory – no guessing whether “Rosso/Nero” means red/black or red/white. The index matches the page numbers – page 3 for fuse layout, page 5 for cable colors. If you’ve ever bought a third-party wiring diagram that rearranged the fuse numbers, you know the frustration. This manual keeps the original layout. It’s 34 pages, no missing sections, no watermarks.

Does this wiring diagram include engine torque specifications or fluid capacities?

No. This is strictly a wiring diagram. It covers electrical circuits only. For torque specs and capacities, get the separate Ferrari 328 GTB & 328 GTS Technical Specifications Manual.

What languages are in the document?

The manual is trilingual: Italian (primary), English, and French. All figures and labels appear in three languages side by side. The fuse table on page 4, for example, lists each component in both Italian and English. If you’ve ever tried to splice wires using a manual in a foreign language, you’ll appreciate having the English translation right next to the schematic. The cable color codes are in Italian, but the English color names are shown in the “Cable Colors” section. So you don’t need to memorize that “Marrone” means brown. It’s all cross-referenced.

If you’re getting under the dash of a 30-year-old Ferrari, don’t trust a photocopy of a copy. Access the Factory Manual – the original 1989 wiring diagram – and keep it on your tablet or print it out for the bench. It’s 34 pages of factory-sourced data that will save you the cost of a new ECU.