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MG Midget and Sprite Technical - Strange electrical problem

I went to go out for a drive last night and car would not start nothing not even a click ,so assumed it was a flat battery, so put it on charge. I Went to start it today and no change so checked battery voltage and 13.2v so tried lights and nothing so after testing a few things found the main earth to the body was bad unbolted it and there was a slight mark on the washers nothing that you would think was bad enough to not connect so cleaned everything up and all is fine,the car only was only rebuilt last year and everything looked shiny and new. I have sealed the new connection as per an aircraft ground,I still could not believe it just failed like it did .
mark heyworth

Corrosion creeps up on you. It doesn't take much. And living in a moist environment doesn't help. We get a lot of rainy and cloudy days here so that's always a threat. Sealing the connection like you did should help a lot and if it ever happens again you'll know what to look for.
Martin

What surprised me is how quick it creeps up on you this is a photo taken when it was fitted in February 2022

mark heyworth

I had that happen to me once but it was the positive terminal to battery connection. A quick twist of the terminal after loosening the retention bolt and the problem went away. I cleaned everything up and it worked as it should.
Martin

Mark
Has the paint been removed on the metal where the bolt/ washer contact it? It needs to be and also should be clean and shiny.
Bill Bretherton

yes all was cleaned not sure what happened, must just be one of the infamous lucas faults
mark heyworth

A lot of people use shakeproof(star) washers between the terminal and the body on restorations so that the paint doesn't need scraping back--all the little sharp points of the star washer are enough to get through the paint to earth
On the same issue-
I had to go over to the boat and get a new truck started one day here a bit back---so this thing had been started at the Ford company, probably more than once and taken to the wharf and started there again to load it up (RORO) and started in the ship to unload it but when they went to deliver it -nothing
Went over ,checked the battery,ok, checked for loose battery leads,ok -thought loose wire on the starter so underneath and checked-tight-hmmm, got the meter out no power at the starter, followed it back and no power at the battery connections but the battery was good and the terminals tight and squeaky clean--pulled the terminals off and found although they looked all sparkly clean as you'd expect from a new vehicle they weren't making contact, turned out that the end connectors on the wires had been painted with some sort of clearcoat to protect them, cleaned it off the faces of them and bolted it back together and bingo--all good
William Revit

It all boils down to having a good ground, Lucas or any other electrical system.
Martin

I've noticed twice now that some pre-engaged starter solenoids have a separate dedicated earth wire instead of relying on earthing through the starter body.
Both were transverse Ford van engines and both used crappy cheap crimp connectors.
Easy fix though and it makes you look good when you get it going in under a minute!
Greybeard

Here's a good one for you Grey
I've been doing some jobs on a fella's GT40 which runs a Motec management system---Have had a hell of a go trying to get the cold starting sorted. Kept coming up with a code for camshaft timing
The electrics were showing heaps of static/false signals on the cam sensor line, the crank sensor was perfect---tried it with the cam sensor disconected and still static--checked the main earth cable, all good and nice and short just being a bridge accross an engine mounting---anyway finally decided it was static from the starter motor getting into the wiring loom as you could see the static waving up and down as it came to each compression stroke
Tried a seperate battery with jumper leads direct to the chassis and the + connection on the starter---same
Moved the jumper lead neg. lead to direct on the starter housing, and bugger me all the static went away
So instead of having the earth cable looped around the engine mounting it's now direct from the battery/chassis onto one of the starter mounting bolts and it starts first try every time and no static on the cam sensor line--
Rang the dudes at Motec and told them and the answer was, yes mate the earth needs to be on the starter because cast iron engine blocks aren't good conductors
I'd never heard of that before i didn't think---but you mentioning Ford vans just reminded me--Ford here recalled loads of Transit diesels to have the earth lead moved from the block direct onto the starter to fix starting issues----wish i'd remembered that a month or two ago
willy
William Revit

Willy
Interesting. Also, with poor starting say there was a contact or path resistance of just 0.1ohms on the starter circuit. 100A, which is possible starter current, across that gives 10v volt drop - clearly unacceptable. But even 0.01ohms gives 1v volt drop which you don't want and would rise to 2v for a 200A starter. I wonder how many vehicles are "suffering" from this.
Bill Bretherton

Having a think about it today and i am wondering if having it on a battery maintainer plugged into aux socket all winter has had something to do with the build up of resistance in the main ground
mark heyworth

My Sprite has a Heritage shell and the factory primer is certainly non conducting and is difficult to remove when you are making an earth.

Jan T
J Targosz

Willy said-

"yes mate the earth needs to be on the starter because cast iron engine blocks aren't good conductors"

Very common problem on old (Series) Landroversauruses. The last one I owned had at least four earth straps in various places.

But I didn't know that about iron blocks. Interesting.
Greybeard

This thread was discussed between 20/04/2023 and 22/04/2023

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