Description

BMW 735i, 735iL, 750iL 1988 Troubleshooting Manual

If you’ve ever stared at a nest of wires under the dash of a 1988 BMW 750iL and wondered which one goes where, you’re not alone. I’ve pulled more than a few aftermarket “electrical guides” that had the pinouts flipped. Waste of time. This BMW 735i, 735iL, 750iL 1988 Troubleshooting Manual is what the dealer techs used when these E32s were new. 495 pages of factory-original troubleshooting – no reprints, no guesswork, no third-party redraws. If you’re working on a 735iL with a no-start or a 750iL with a dead ABS module, this is the only book that matters.

Section 0670: Power Distribution – Where It Starts

Voltage drop hunts are the first thing I teach junior techs. Section 0670-00 lays out the entire power distribution diagram for the 735i, 735iL, and 750iL. Fuse details? Pages 0671-00. Ground distribution? Section 0672-00. You need to know where the main power feeds split for the ZKE module and the DME relays. This manual gives you the exact wire colors and splice locations – not a generic schematic that shows a generic bulb. I’ve used this to chase down a parasitic drain on a 750iL that had three different control units sharing one ground. Fixed it in forty minutes.

Check the Ground Distribution First

Lazy guesswork starts with throwing parts. Smart troubleshooting starts with verifying grounds. Section 0672-00 lists every ground point for the E32 body. The 750iL V12 has a separate ground strap for each bank – if one corrodes, you get misfires, transmission limp mode, and a check engine light that makes no sense. This manual shows you exactly where G102, G201, and G301 live. Save yourself the headache.

3 Systems That Will Leave You Stranded Without This Manual

First, the Antilock Brake System (ABS) – section 3450-00. The E32 ABS controller is notorious for failing solder joints. The manual gives you the diagnostic link pinouts and the sequence for bleeding the modulator. Second, the Electronic Throttle Control (EML 1.2) – section 1375-00. On the 750iL, if the EML loses its position signal, the car goes into a hard limp mode. You need the factory test procedure. Third, the Central Body Electronics (ZKE) – section 6100-00. The ZKE controls windows, locks, sunroof, wipers. If the module goes bad, you can’t even roll down a window. This manual walks you through the input/output tests at the module connector.

Injection Electronics: DME 1.1 vs DME/EML 1.2

The 735i uses DME 1.1 (section 1360-00). The early 750iL uses DME/EML 1.2 (section 1366-00), and late production 750iL switches to a revised DME/EML 1.2 (section 1367-00). The pinouts are different. The crank sensor wiring changed. If you have a late 750iL and you use the early diagram, you’ll be chasing a ghost. This manual clearly separates the two with separate sections. No confusion.

Source Authenticity: Factory OEM vs Aftermarket Trash

I keep a shelf of aftermarket wiring books. They’re fine for general reference, but for the 1988 BMW 7 Series, half of them get the ISO 9141 diagnostic connector wrong. This manual is a direct scan of the factory binder BMW issued to dealers in 1988. Part number 89 89 1 000 825. The component location chart (section 7000-00) and connector views (section 8500-00) are photographic quality – you see the actual connectors, not a cartoon. If you’ve ever tried to match a wire color from an aftermarket manual to a 30-year-old harness, you know the difference. This is the real thing. For more recent model years, check out the BMW 7 Series 1988-1994 Service Manual or the specific BMW 735i 1988 Electrical Troubleshooting Manual. The 1990 edition is also available: BMW 735i 735iL 750iL 1990 Electrical Troubleshooting Manual.

Who Needs This? The Home Mechanic and the Pro

If you’re a home garage enthusiast with a 735iL that won’t crank, this manual gives you the starting system test sequence (section 1240-00) and the charging system checks (section 1230-00). If you’re a pro tech billing by the hour, you can’t afford to guess on the EML throttle calibration or the ABS wheel speed sensor resistance. The manual lists the test specs in the troubleshooting tables. No fluff. I’ve used it to diagnose a no-spark condition on a 750iL by checking the E-box fan operation (section 0690-00) – the fan failure had overheated the DME. Wouldn’t have caught that without the factory systematic approach.

FAQ

Does this manual cover the 750iL V12 engine?

Yes. It covers both early and late production 750iL with separate sections for DME/EML 1.2.

Can I use this manual for a 1990 model year E32?

This manual is specifically for vehicles produced between September 1987 and August 1988 (model year 1988). The wiring, fuse assignments, and control module pinouts changed in 1989. For a 1990 model you need the 1990 edition – check the separate BMW 735i 735iL 750iL 1990 Electrical Troubleshooting Manual. I’ve seen guys swap the DME from a 1988 into a 1990 car and fry the harness because the injector wiring is different. Do not use this manual for later years.

If you’re serious about electrical diagnostics on the E32 7 Series, you need the factory data. This is the same manual that sat inside every BMW dealership service bay in 1988. Every wire color, every connector cavity, every test voltage. Access the Factory Manual and stop guessing.

For a broader overview of automotive electrical system evolution, see Automotive Industry Overview or read more at Automotive Industry Overview if you want context on why OEM documentation matters.