Hi Theo, thanks for your interesting reply.

I sourced and cleaned the grounds above the fuse board and under the steering column today; they had some corrosion on the wires and the ground points on the body were very dull. I cleaned them up and covered them after with the copper grease. They were a bit tricky to access.

I took pic's of the points I've done so far hoping they will assist someone else who may want to do this work themselves. I've enclosed them. Maybe you can put them in the same order as my write up?

Brief write-up.

Ground point maintenance on a 1990 Rhd 928 S4 with Cat. Tools required: 10mm socket and ratchet with flexible attachment and or spanner; 180 grit sand paper; small brush; copper grease.
 

  1. Disconnect battery. Clean battery ground strap under tool panel. While your there, good to clean up the battery terminals and the positive+negative connectors (including the small ones on the positive).
  2. Remove the plastic cover at the front of the spare wheel well. Inside is a ground point easy to access. Remove the 10mm bolt, Look closely at the ground straps for any corrosion and clean them up to a shine with the 180 paper. Do the same to the ground terminal on the body. It should shine when you've finished. Replace the bolt through the ground cables and screw it back in nice and tight. Cover the exposed part of the body ground and exposed cables with copper grease using the small brush. DON'T GET ANY INBETWEEN THE GROUND CABLE AND BODY GROUND POINT. Replace the plastic cover.
  3. Move around to the engine bay now and begin with the easiest to access; the ground located on the passenger side near to the headlight motor. Repeat above process.
  4. Now look to the driver's side behind the AC pipes; the ground is located on the inner wing. Access is very limited. Remove rubber seal and unscrew the wing nut close to the ground for best access. Using the 10mm socket with an extension and flexible attachment, access the ground bolt from above the AC pipes. Once you loosen the bolt to the point where it's nearly out, you must finish removing it by hand as to not drop it; very tricky but it's possible with the left hand. Repeat clean-up process as above. Replace bolt with care! If you drop it, it will be hard to retrieve.
  5. Now go to the ground above the driver's side coil. Remove the plastic cover and undo the jumper nut. Repeat clean-up/replacement procedure. Replace jumper nut and cover.
  6. Move on up to the suspension turret. Here you'll find a single cable ground attachment; look close to the reservoir for a reference point to help find it. Repeat clean-up and replacement procedure.
  7. Now go over to the passenger side and find the ignition coil. Forward of this towards the Rad is a small black plastic cover holding a brown and red wire. Remove the cover and undo the large hex-head screw holding the two wires. Clean them up and the lower holding bracket the large screws go into. Replace and protect.
  8. Move up to the passenger side suspension turret and find a single ground as on the driver's side. Repeat clean-up and replacement procedure.
  9. Move on to the passenger side fuse and relay board inside the car. The grounds here are located at the bulkhead above the fuse panel; there's two. Remove parcel shelf and any electrical boxes restricting access; CAREFUL WITH ANY WIRING! The number of ground wires on the right side is huge and the bolt is very long. Check the wires here carefully as corrosion can be difficult to see as there are so many wires and access is difficult. Repeat removal, clean-up and replacement procedure. Replace any parts removed for access.
  10. Go round to the driver's side. Remove parcel shelf and stick your head under where the brake pedal is and look back at the steering column; the ground point is there on the right side. Again, access is limited and awkward. Repeat clean-up/replacement procedure.
     

There's 3 more to do; when I've done them I'll add pic's/info! Hope this helps someone else new to this work. It definitely makes a difference. My volt meter on the dash was always at 12; now it's between 12/14.

Best, Dave.
 

 

MP 1 -- at the headlight tube, close to ignition power stage

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MP II -- next to the top of the radiator at the passenger side, close to the transmission cooler lines

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MP III -- hidden below the jump post terminal assembly

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MP IV -- driver side footwell behind the parcel tray, near steering column

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MP V -- Above the fuse panel---

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MP VI -- under the cover in the spare wheel well.

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MP VII -- at battery ground strap

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MP X -- at coil near the ATF steering reservoir

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MP  XI -- suspension strut driver side

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MP  XII -- suspension strut passenger side

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