Weird electrical fault, suggestions please

[Rata Road]

1951 Rover 75, all factory, 12v Positive earth. Was driving fine when parked up in a dry rodent free garage.
Battery under rear seat.

Rover has been in dry storage just over a year and found this issue when I got it out today.

Battery is charged.

When Key on the ignition and oil light glow bright, I then press starter and nothing happens and lights go out.

Turn the key off and on again and both lights dont glow now. After a minute the lights will glow and the same thing happens again and sometimes a battery lead needs off and on to get the ignition lights to come on again.

I tried the same again but this time dont touch the starter, i tried the Horn and the ignitions lights go out. Exactly the same fault this caused by tooting the horn.

The ignition lights wont come back on doing this either.

Today I tried the following -
Battery ok and fully charged.

I removed the earth strap from the battery and cleaned up and refit, charged the battery again and cleaned up all terminal connections, no difference with same fault with ignition lights no coming back on.

The main power from the battery goes to the Solenoid via a thick cable and with this still attached to the solenoid there is no voltage reading on this wire even though it is attached to the battery.

I tried removing the other side wire from the solenoid that goes directly to the starter and this made no difference so the starter shouldn't be the problem.

I then removed this first wire (which goes directly to Battery) from the solenoid and it now has power. Refit to solenoid and the same wire has no voltage.

I then removed the larger of the 2 wires (Lets call it wire A, seen disconnected in pic below)) which is attached on the same terminal that the main power comes in (or being positive earth goes out) and I now have voltage at the solenoid on the main wire when attached to the solenoid , refit this wire and the voltage goes away. So the problem or short is along this wire.
(Being positive earth could this just be a lack of an earth somewhere along this wire?)

However with this wire disconnected from the solenoid nothing goes, ign lights etc, so I guess this is the main power source to the dash, ign etc.

The car has 2 fuses on the voltage regulator and removing these does not remove the fault.

Do I need to disconnect everything behind the dash one at a time.

The interesting thing is with Wire A disconnected meaning there is now power to the incoming side of the solenoid and the other side connected which goes directly to the starter I placed a bar across these 2 solenoid terminal and the starter didn't activate. I realize the car might not start up but I thought the starter would wind over?

Any suggestions on where to look next please?

 

[Bernd]

Are you sure that the battery is ok? I would get a jump start from another car.

 

[cobraboy]

If the battery was left for a year was it connected to a conditioner / charger ?
If not try another battery.

 

[sdibbers]

As the others say, that’s sounds like a battery going down. It probably reads 12v still but has no amperage.

Either that or the ECU (joke!)

 

[bobbymac]

I would have to agree: typical symptoms of either not enough power from the battery or no capacity in the circuit due to an earth fault. In this case it would suggest the battery earth strap but you have already checked that. Is there an earth strap between engine and body? It really points to battery.

 

[Rata Road]

I am about to check find and check earth strap to engine plus I will fit a good working battery from another car.
Thanks for your prompt response guys

 

[jp928]

Good practice with electrics in little used cars is to annually clean battery connections and earth connections - disconnect, clean with abrasives, apply Deoxit or similar, lightly grease battery terminals, rough up the insides of the battery cable fittings. This certainly sounds like a dud battery - shows as charged but cant deliver any current. It may also pay to pull, clean and refit fuses. If you ever convert it to neg earth remember to reverse the coil connections - they are probably marked + and - . Check earth strap for continuity - they sometimes suffer corrosion.
Here is the 50 model I had once - 90 engine and grille, P3 gearbox with over drive, P5 front drum brakes, superb car.

 

[Rata Road]

Thanks JP928.
My car is completely original except a 1957 Rover 75 engine was fitted, but the car came with the original complete engine.
The previous owner died in his 90's and had it for 61 years and it was always garaged. Dash is lovely, tidy car all-round.
No salt used in NZ so underneath is great, things undo easily.
The first owners wife didn't like the colour of their new car so it was painted cream. Two more short term owners before previous. I was talking to his son and he recalled one day when they were polishing the car with Dad the cream paint was polishing off so they cut it all away revealing the original paint.

Update -
Eureka!

I found the fault but it but it was pure luck.

Today I replaced the battery with a bigger stronger unit out of a running car with no advantage.

I then got some heavy duty jumper leads and planned to connect positive terminal on battery "which is earth" to the engine.

The Rover is parked in a dark garage and I'm using headlamps, The Rover has rear interior lights on each side behind the doors. These lights and nothing else electrical was working at the time.

I opened the rear door to get access to the battery terminal under the seat, as I connected the jumper lead spring clamp onto the positive battery terminal I noticed the interior light above me come on. Remembering the replacement battery had both battery wires fastened tight.

I removed the jumper lead clamp and the light went off?

I refitted, the light come on so I tried the dash, all lights working and the starter wound over!

Yesterday I had removed this earth strap, cleaned up all connection including inside the battery connector and around the battery post.

I never would have thought of this being the cause, just luck the car had a working interior light and the car was in a dark garage.

On inspection the existing battery lead connector looks fine to the eye.

So I removed the earth lead and found a brand new replacement the correct size in my parts, fitted that and problem solved.

Very happy

Thanks for your input guys.