Description

BMW 735i, 735iL, 750iL 1991 Electrical Schematic – Factory Troubleshooting Manual

You’re working on a 1991 BMW 735i, 735iL, or 750iL and the electrical system is doing things no circuit should do. You pull an aftermarket wiring diagram off some forum and find out the pin colors don’t match. I’ve been there. That’s time wasted, and in a shop that’s money lost. This is the real deal – the factory Electrical Schematic manual, directly from BMW. 592 pages, published in 1991, covering vehicles produced from 9/90 to 8/91. No reprints. No generic third-party compilation. OEM documentation that matches what the dealer techs used.

What’s Actually in These 592 Pages

The table of contents reads like a tower of Babel for BMW electrics. You get full power distribution charts (section 0660), fuse chart (0661), ground distribution (0672), and every subsystem from the charging system (1230) to the injection electronics (DME 1.3, DME/EML 1.3, and DME/EML 1.7 in sections 1360–1367). Need to trace the Electronic Throttle Control? That’s 1374–1375. The ABS system (3450) and automatic stability control (3451) are laid out with exact wire paths. Central Body Electronics (ZKE) covers door locks, power windows, sunroof, wipers – all in section 6100 and its sub-sections. Component location views (7100), splice locations (8000), and connector views (8500) round it out. This isn’t a service manual – it’s a full electrical troubleshooting guide.

Why Aftermarket Manuals Get You in Trouble

I’ve had techs bring me a car that still had a short after replacing three modules because a Haynes diagram swapped the power feed and ground. Factory manuals like this one show the exact pin assignments at every connector, the correct wire gauge, and the official diagnostic flow. Section 0130 is “Systematic Troubleshooting” – it tells you the OEM method for isolating a fault, not some generic “check voltage here” routine. The symbols legend (0140) defines every icon BMW used. If you’re chasing an intermittent issue in the 750iL’s dual-battery system or the 735i’s ZKE module, you need the real thing.

3 Systems That’ll Bite You Without Factory Data

Let’s talk specifics. First: the ABS and ASC+T (sections 3450–3452). These cars have traction control that ties into the throttle and brake systems. One wrong wire tap and you can disable the whole system. Second: the Electronic Transmission Control (EGS/EML) – sections 2460 and 2465. The 750iL uses a combined EML throttle and transmission controller. The schematic shows exactly how the DME talks to the EGS. Miss a ground at the right pin and the transmission won’t shift right. Third: the Central Body Electronics (ZKE) – section 6100. This controls the door locks, windows, sunroof, central locking, and interior lights. If the sunroof doesn’t close after a battery disconnect, the ZKE module needs a specific reset procedure. The manual has the procedure and the wiring to check for stuck relays.

Systematic Troubleshooting: The Right Way

Section 0130 is one of the first you should read. It lays out a five-step diagnostic method: verify the complaint, check basic power and grounds, isolate the circuit, test components, and confirm repair. That’s exactly how I train my junior techs. Pair that with the fuse details (0671) showing which fuses protect which circuits – for example, fuse 7 covers the auxiliary fan, fuse 9 the brake lining warning. Page 2 of the index lists every system and its section number. You don’t flip pages randomly; you go straight to the subsystem you need.

Get the Right Specs – Beyond the Schematic

This manual covers electrical diagnostics only. If you need mechanical torque values or engine overhaul procedures for these BMWs, you’ll want the companion service manual. Check out the BMW 7 Series 1988-1994 Service Manual for that. For earlier model year electrical problems, the BMW 735i 1988 Electrical Troubleshooting Manual and BMW 735i 735iL 750iL 1990 Electrical Troubleshooting Manual are also available on this site. For broader context on vehicle electrical systems, the Automotive Industry Overview and Automotive Battery pages can provide background, but for diagnosis, you want the factory schematic.

Frequently Asked Questions

Does this manual cover engine mechanical repairs?

No. This is an electrical schematic only – no torque specs, no engine teardown steps, no fluid capacities.

What is the difference between this and the 1990 version?

The 1990 manual covers vehicles produced from 9/89 to 8/90. This 1991 version covers 9/90–8/91 production. BMW made changes to the DME/EML controller during that period – the 1991 manual includes the DME 1.7 variant (section 1367) which the 1990 manual does not. Also, the 1991 edition adds the Electronic Throttle Control (EML) section 1375 and revised ABS/ASC+T wiring. The fuse layout changed slightly; for example, the 1991 manual shows a different assignment for fuse 10 (now covers the cellular telephone provisions instead of something else). If you have a late-1990 build car, verify the production date – cross-referencing both manuals might be necessary. But for any 1991 model year car, this is the one.

If you’re tired of chasing electrical ghosts with incomplete data, this manual gives you the exact tool to work smarter. Access the Factory Manual and get the wiring straight before you touch another connector.