Smoke from engine bay, start motor? HELP!

[Sweeny]

To the good and knowledgeable people of the MMOC, I've just had a major scare with the 'old girl'. I tried to start my 1968 Morris Traveller, as I have many times before but this time seemed different. She gave the impression of a flat battery, being very reluctant to turn over (I know for a fact the battery is of good condition and sufficient charge having started her the previous day). The next thing I know smoke comes pouring out from under the bonnet, being paranoid about the possibility of a fire I kill the ignition, jump out the car open the bonnet ready to jump for my extinguisher and wait for the smoke to clear, disconnect the battery and take stock. There seems to be no damage (superficially at least) to the starter motor however I find the earthing wire for the fuel pump has been burnt through completely and the negative terminal shows signs of slight damage too (see pics for more info). Can anyone advise to a cause of this occurrence? Would it be sensible to implement in line fuses to certain parts of the wiring loom if so to which locations?
Thank you in advance to all help
Tom

[oliver90owner]

I would hazard a guess that your earthing lead from battery to frame/engine is about done for, resulting in current flow to the earth side of battery through any thin wire it can use, resulting in the fried insulation on that (and possibly other) wire(s). I once found the starter motor current returning via the fuel pipe. No particular ongoing fault, once the earth is restored, as any earthing wire could be uninsulated!

Other alternative is a dead short in the pump.

RAB

[Biggles1957]

My first port of call would be that earth connection from the battery to the body. Take it all off and really clean everything back to bright metal. I had a similar 'burn-out' through the choke cable on an old car once because the earth wasn't good enough.

[Sweeny]

Thank you all for your replies, I have stripped that earth cable down and cleaned it thoroughly. Do correct me if I'm wrong but I couldn't work out what that cable's purpose was? The fuel pump would be getting it's earth from the bodywork its bolted to so what would that cable be supplying? Would it be best to negate that cable and assume it was a non original add-on?

[shoebone]

The fuel pump needs an earth because there is a rubber diaphragm in the pump which effectively isolates the business end of the pump where the electrical contacts are. You should also have a good earth strap from the body to the engine/gearbox.

[Sweeny]

Thank you for the reply sheobone, the fuel pump presently works due to (and I'm guessing) it being earthed through the battery casing I've bolted the pump too, would this be sufficient to supply the charge it needs or would I have to replace the burnt out wire, I still have doubts to the purpose of that wire. The earth strap (the wire under the car going from the gearbox support mount to the back of the gearbox) has had a thorough clean, would it be advisable to fit a secondary wire on the opposite side of the gearbox to make sure a solid earth is supplied?

[andy.pointeer]

Hi, have you checked the earth strap from the gearbox to the bodywork at the back of the gearbox. The engine/gearbox needs a good earth to the body for the starter motor to get a good earth.

[Sweeny]

Yes I have checked that wire, I will check it again however, can't be too careful!

[oliver90owner]

There are several screws through the fuel pump body, any one of which could effectively earth the pump. But that depends on the pump mounting. If someone used nylon nuts to an insulated attachment plate, the pump could be left without an earth path back to the battery. Unlikely but possible, so a dedicated earth connection was provided.

Don't know about Morris vehicles, but Ford used to be clever enough to connect the battery earth to the engine/gearox (with only the lower amperage items using the car chassis as an earth return via the engine/gearbox earth strap).

RAB

[graham1957]

its that bolt connection to the side of the battery box which has caused the fault, clean the paint off around that hole and replace the earth wire to the pump and all should be ok. the thick earth cable from battery has been making a poor connection to the body just there but making a reasonable connection to the black wire to the pump and going to earth through pump hence heating up the thin pump earth wire, graham

[Sweeny]

Many thanks to everyone for your replies. I now have a cleaned earthing connection and a checked earthing wire (between gearbox and gearbox mounting bracket), tried to start the old girl up and success! I'm now going to take some time to go through putting in line fuses into the loom.
Cheers,
Tom