Ground points guide
A bad ground is behind more strange electrical faults than anything else on a car this old: dim or flickering lights, gauges that misbehave, a starter that will not turn, even a car that will not start. This guide shows where the grounds are, what each one feeds, and how to test and clean them.
Why grounds fail
A ground wire completes every circuit. Where it bolts to the body there is a joint of metal, paint and rust. Over thirty years the joint corrodes, and the extra resistance makes everything on that ground behave as if it has a low or noisy supply. The fault can be intermittent, getting worse when damp or hot, which makes it hard to chase from the load side.
The ground points
These are the grounds drawn in the factory manual, with where each one is and what it serves. Locations are as printed on the ground distribution pages; confirm them on your car. Several of the ground pages split the same ground into more than one drawing, such as "G200 partial".
| Ground | Where | What depends on it | Wiring |
|---|---|---|---|
| G100 | Battery negative to the body | The main negative path for the whole car. Starting, charging and every circuit return through it. | 0670-2 Power Distribution (2.7e/2.5i) |
| G103 | 2.5i: on the right shock tower. 2.7e: left side of the engine block, above the starter. | Engine computer, diagnostic connector, main relay, sensor shield grounds, idle control and the injection electronics. | 0670-13 Ground Distribution G103 |
| G104 | On the inner wing, behind the left headlights | The ABS hydraulic unit, the brake warning circuit, horn and check control circuits. | 0670-14 Ground Distribution G104, G106, G200 |
| G200 | Under the left side of the dash, above the brake pedal (drawn in several parts) | The big one: instrument cluster, start relay, central locking, power window switches, ABS control unit, on-board computer relay box, interior lights, the radio and many more. | 0670-15 Ground Distribution G201, G200, 0670-16 Ground Distribution G200, G300 |
| G201 | Upper left of the steering column | Horn switches, wiper and washer switch, turn signal flasher, combination switch. Joined to G200. | 0670-15 Ground Distribution G201, G200 |
| G202 | Below the right side of the rear seat | The auxiliary fuel pump ground and rear wiring connector C307. On some versions the fuel tank sender returns through it too. | 0670-19 Ground Distribution G300, G202 (Convertible) |
| G300 | Under the left side of the rear seat back | The main and auxiliary fuel pumps, the high-level brake light, the rear lights check relay, the fuel tank sender and the rear window blower. | 0670-16 Ground Distribution G200, G300 |
| G106 | Location not given on the diagram | The sound-system amplifier. | 6500-1 Radio/Antenna with Sound System |
| G302 | Location not given on the diagram | The power antenna motor. | 6500-0 Radio/Antenna with Sound System (radio) |
| G600 | Location not given on the diagram | The sunroof switch. | 5413-0 Sunroof |
| Case grounds | On the part itself | The starter, the alternator, the compressor clutch, the thermo-time switch and the door jamb switches ground through their own body or case. | 1240-0 Start (2.7e/2.5i, automatic, except convertible), 1230-1 Charge (2.5i) |
The ground distribution pages show how a ground that looks like a single bolt is really a hub: several wires, and sometimes other grounds, join at it. If G200 is poor, a dozen things above the pedals go wrong together.
How to test a ground
You are looking for resistance in the path, so test it with the circuit working. A voltage drop test finds a poor ground even when it looks fine.
- Set a meter to a low DC voltage range (2 V or 20 V).
- Switch on the load, such as the headlights, the fuel pump relay jumper, or a crank attempt.
- Put one probe on the ground point's bolt (or the ground terminal's housing), and the other on the battery's negative post. Use a long lead.
- Read the meter. A good ground reads close to zero, under about 0.1 V for a light load and under about 0.3 V while cranking. More than that means resistance in the ground path.
Compare the reading with the same test on the negative cable at the engine and at the body. A large reading at the body ground and a small one at the engine tells you which half of the path is poor.
Cleaning and repairing
- Disconnect the battery.
- Undo the ground bolt, and remove the ring terminal. Clean the terminal and the body contact area to bare, shiny metal with a wire brush or abrasive pad. Remove paint and rust, but not more metal than needed.
- Refit the terminal with a star washer, and tighten it firmly.
- Seal the joint from moisture with a thin layer of dielectric grease or a ground-safe sealant, once it is bolted tight.
- If the wire's insulation is cracked or its strands are green and brittle, replace the wire and terminal. Crimp it with a proper tool and cover the joint with adhesive heat-shrink.
- For a car with a poor engine-to-body path, add or replace the ground strap between the engine and the body.
Symptoms and the ground to suspect
| Symptom | Suspect |
|---|---|
| Slow cranking or a click, with a good battery | The battery negative, G100, the engine-to-body strap, the starter case ground |
| Starts badly, runs rough, odd sensor readings | G103 (engine computer ground) |
| Fuel pump weak or intermittent, high brake light out | G300 under the rear seat |
| Fuel gauge wrong or jumping | G300 and G202 in the rear (the tank sender returns through them), and G200 at the cluster |
| Gauges, dash lights or windows misbehaving together | G200 under the dash |
| Horn or wipers erratic | G201 on the steering column |
| ABS or brake warning light odd | G104 behind the left headlight |
| Radio noise, amplifier dead | G200 and G106 |
| Dim headlights or lamps that flicker | Body grounds near the lamps, then G104 and G200 |
If the symptom is a car that will not start, the no-start guide checks these grounds in order.
Written from the factory wiring diagrams on this site and general diagnostic practice. Voltages, resistances and pressures are typical figures, so confirm them against your car's manual. Take care with fuel, high voltage and the battery.