Bad Earth Problems

Batteries, Alternator, Wiring, Lighting, etc. (Please discuss ignition problems in the Engine category)
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osholt
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Bad Earth Problems

#1 Post by osholt » Sun May 21, 2017 9:20 pm

Hello,

What started as a 'simple' job to swap out the radio and the dashboard has ended up being a wiring disaster.

I believe the problems are caused by a bad earth which I have managed to disturb in the disassembly process. The interior light works sporadically but most of the dash warning lights, and none of the steering column switches appear to operate anything. If I connect a wire directly from the battery negative to the cigarette lighter negative the windscreen wipers do operate but nothing else. All the wiring up to and leaving the fusebox seems to be in order.

Does anyone have a list of all the earthing points, particularly ones behind the dashboard and centre console? I could not find this information in my workshop manual.

Any other suggestions are welcome

Thanks,

Oliver
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osholt
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Re: Bad Earth Problems

#2 Post by osholt » Fri May 26, 2017 8:48 pm

I found the cause of my problems. It's a weird one, at least in my experience.

The very short earthing strap from the battery negative to the suspension turret was not connected when I bought the car. I now realise this was becuase the battery terminals were on the side facing towards the centre of the car so it would not reach the suspension turret.

At some point one of the previous owners disconnected this innocently when replacing the battery and discovered that all the lights and indicators etc. still worked.

I thought I had a totally unrelated problem where the end of the throttle cable nearest the pedal had its plastic sheath buckle resulting in the throttle pedal not moving; I thought this was becuase it had been damaged while being fitted by a previous owner. I removed the throttle cable at the same time I started fiddling with the radio and dashboard.

It turns out that the throttle cable was probably the only good earth connection for everything except the starter motor which might explain why the sheath buckled if it got very hot with all the lights on becoming soft and brittle.

Retrospectively it makes sense: when I removed the throttle cable (and the choke cable for good measure while removing the centre console) suddenly none of the lights, horn, indicator or anything else worked! Their only return path was via the metal cables going to the engine.

I will be purchasing a new battery very soon and connecting the earth strap properly and I can then finally reinstall the dashboard and centre console without fear of nothing working again.
Register Member No. 7822-01/17

Triumph 2000 Mk2 Sapphire Blue (1972)
Triumph TR7 Convertible Persian Aqua Blue (1980) - Press car under restoration
Mini Clubvan Cooper D Ice Blue (2012)

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Dave B
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Re: Bad Earth Problems

#3 Post by Dave B » Sat May 27, 2017 2:47 am

Also check the speedo cable has not been acting as an earth return, you've just reminded me I had a similar problem with a Mini Cooper back in the '70's, so much so that the speedo needle gave off a puff of smoke and then fell off!
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David Withers
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Re: Bad Earth Problems

#4 Post by David Withers » Sat May 27, 2017 8:05 am

osholt wrote:I found the cause of my problems. It's a weird one, at least in my experience.
<snip>
It turns out that the throttle cable was probably the only good earth connection for everything except the starter motor...
I had exactly the same problem many years ago on a Morris 1100. I had wondered (a) why the lights weren't very bright and (b) why the throttle cable was dry and rusty not long after being oiled. Lifting the bonnet with everything turned on revealed a red hot throttle cable!

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Re: Bad Earth Problems

#5 Post by wild bill » Sun May 28, 2017 5:09 pm

Had the exact same fault with my first or second Minivan circa '72/73. Think I was also stupid enough to not believe that it WAS hot and put a lovely burn line across all my fingers! :?
Don't think Iv'e learnt much yet!!!........Good old Leyland!!!!!!!!!!!!
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Re: Bad Earth Problems

#6 Post by Clifford Pope » Sun May 28, 2017 5:29 pm

I had the same thing with a Ferguson tractor. The battery earth went to a bolt holding the fuel tank to the bulkhead, but the bulkhead was isolated from the engine/gearbox because the bolts and washers were corroded. The fuel pipe from the tank on top of the engine to the carburettor supplied the earth.
If the engine didn't fire immediately prolonged cranking heated the fuel pipe. I discovered this when I burned my hand on it.

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