Team

Another one for the Series electrics experts. It's a Series 3 109 24v. A while ago I had an issue with instrument earths where the fuel and temp gauge would go up to max, and the map light stopped working. There were two or three earth wires to the metal part of the top dash behind the centre console. There is no voltage stabiliser behind the instruments, allegedly 24v versions don't and the wiring diagram for the vehicle and the parts book both back this up - the 24v instrument panel parts illustration has no stabiliser on the diagram where the 12v version of the drawing does. No I don't know how the instruments work without a stabiliser.

All this was fixed by running an earth from the dash earth bolt on the dash direct to the bulkhead. The map light started working, and the instruments behaved themselves.

But I've noticed when I put the headlamps on, the charge light comes on at various times (not all the time), and when it does the temp and fuel gauge go up to max. If I use the indicator with the headlights on, the charge light sometimes flickers on and off in time with the indicators. The alternator is putting out a rock solid 27.1 volts and the alternator is almost new.

I tightened the battery earth cable.

The batteries are probably not long for this world as they were overcharged by the previous alternator before we worked out what was happening.

I'm thinking the batteries might be starting to fail or possibly another earth issue unless someone else has any ideas. My question is, where should I run new earths from?

Any suggestions gratefully appreciated.

Hi
I would run a substantial earth cable from the battery to the Bulkhead and while doing this remove, clean and refit the battery earth to chassis lead

I've searched this topic many times but just found the thread linked below which I've never seen before. Worth linking here because it covers the issue really well:
https://www.landyzone.co.uk/land-rover/bad-chassis-earth.323300/

But in terms of the solution, what @Mark Frewin said above covers it.

Following the advice from @Mark Frewin and the thread linked above, I've done two things:

I cleaned up the battery neg to chassis earth cable. There was some surface corrosion under the bolt head and washer, so polished everything up and all is nice and shiny now, protected by grease. Seemed to be a definite improvement. Started easily, smooth idle, and the movement of the gauge needles was much less (but still there slightly), alt light flickering much reduced.

The second thing is I found a spare 50mm2 cable from the alternator replacement project which was slightly too short for my alternator positive. I attached one end to the bulkhead where the bonnet earth braid attaches, and the other to the chassis using an existing bolt. I've just finished this a few minutes ago so haven't tested it yet, but the bulkhead must be well and truly earthed now.

I'll test and take some multimeter readings and update this thread. Before I started it was charging 27.1 volts which was probably on the low side - I'm sure when I first installed the new alternator it was 28-point-something volts.

Next step is to undo the engine to chassis earth cable and clean up both ends. While it looks OK, a clean-up can't hurt.

I hate peoples showing off with working bulbs and the like.

well if it makes you feel better I sheared off the connector for the electronic ignition earth as I was tightening the engine block earth I'd cleaned up so it's immobilised now until the connectors and heat shrink I've ordered arrive later in the week (hopefully)!

Hmmm, it is still doing it despite the cleaned up earths (engine block to chassis and batt neg to chassis) snd the addition of a bulkhead earth.
I'll take a closer look at the earth cables and condition.

Sounds like a short behind the dash to me.

Could be the case as the ammeter illumination light shorted a few months ago and I burned a couple of wires. I also had some shenanigans straight after fixing the wiring where the fog light switch bulb and the map light stopped working. Map light was restored to operation by running an earth wire from the dash earth point to the bulkhead.

OK I found a black wire coming through the grommet from the headlights running back to a ring terminal on the steering box. Ran a wire from that to the bonnet earth strap bolt on the bulkhead in case it helped. Still doing it. Did voltage readings from batt neg to chassis and engine block to chassis. No discernible readings. Charging under load is 27.1v (it is a 24v system) which seems on the low side of OK. I'm sure it was around 28v when I installed the alternator a couple of years ago. But I saw on a Youtube video about rewiring a Series 3, the instrument earths x2 are common with the inspection light earth socket. So I took voltage reading from inspection light earth socket to a bolt on the bulkhead and got readings in the range of 0.07v - 0.22v. I'll check the thread I linked above to see if I can work out what it means,

It means the earth for the socket your testing from has a high resistance to earth , or should I say by comparison to your meter earth connection. Mind the volage your reading is not very high can you push an earth wire in the inspection lamp earth connection and conect to wing and see if fault goes away. Could alos be a high resistance on wing if any lights on wing where powered.

Thank you.

I followed that suggestion last night; with the engine running and lights on I pushed a wire into the inspection light earth socket on the instrument binnacle and earthed it on a bolt on the bulkhead, and the fuel/temp gauges dropped to the bottom of the red zones, removing it they went back up, repeated this several times. So while there is a definite effect they didn't go all the way back down to normal, but might do so with proper clean connections rather than being held in with fingers!

Therefore, the next port of call is the instrument casing earths which also connect to the inspection socket earth.

To round this off, while replacing the lower dash on the weekend I used the 0.75-inch extra access behind the instrument panel to check the instrument earths. They are held to the back of each dial with a knurled aluminium knob on a steel thread with what looks like a copper piece for it to tighten against. There was white fur corrosion around the knob, and the ring terminals were definitely not bright. So I cleaned up the ring terminals and the alloy knurled knobs with emery paper, dosing them with B-H Ferrosol on reinstallation. I also made new earths directly from each instrument earth terminal to the bulkhead using a screw into an existing hole behind the cluster. On test driving the vehicle, the irregular rising and falling of the fuel and temp gauges seems to have ceased. Fingers crossed.

It was a bit of a distraction while driving as it gave false high readings and I was always wondering if it was actually overheating not, and how much fuel I had. I'd periodically check using the IR thermometer just in case it wasn't the gauge for once, and I ran out of fuel on one occasion as I had no idea how much fuel was in the tank. So hopefully for my trip to the Classic Land Rover Gathering this weekend the instruments will continue to behave themselves.