Blowing Earth Wire Fuse.

[Guest 2b cruising]

Hi all.

Once again my hatred of the dark side (electrics) is doin me ead in.

 

2ltr DOHC engine.

When going to start it, the motor sounds like it is going to work but pop. A 25 amp fuse under the dash fitted to an earth wire goes.

I used a jump lead as an earth strap from battery to engine and the starter worked ok.

Is the earth switched to protect the old Ford Ecu?

Is the starter faulty and feeding + down the earth side?

I don't mind buying a new starter but would hate it if this wasn't the cure I require.

I also don't want to use a seperate earth if it would just bypass any safety system leaving other equipment open to damage.

Any good advice, would be appreciated.

[speedtripledan]

seems a bit strange to me, i see no reason why it would be that way.

[Guest 2b cruising]

Well there is one there and it keeps on blowing.

I intend speaking to the said pro that messed the rest of it up while fitting the new dash.

Spent all day Sunday putting the rear lights wiring right after two new wings fitted.

Don't ask who but I am peed orf with them.

Possible something they added to protect new gauges.

Edited July 20, 2015 by 2b cruising

[IanS]

Fuses are always in the positive side.

The battery should be connected to the chasies and engine with large cables which do not need protecting with fuses.

Ford fitted a fuse (60 to 100Amp) in the battery positive but the starter does not go through that fuse it has a seperate lead direct from the battery to the starter motor.

Intersetingly the alternator chargeing current does go through the big fuse which is a thin wire incorporated in the non starter battery wire.

[Guest 2b cruising]

Big earth on starter. It just seems to me that this is switched and fused to stop spiking through earth if a short circuit happens.

I have met it many times before on hgv with tanker wiring.

Even on the MAN TG models without pet regs equipment,

These were to protect the sensitive signal wiring and ecu and stuff like that.

I know if you get a large dead short to the chassis, it used to play havoc with any early ecu stuff.

I fully intend to call someone tomorrow. Won't admit to anyone who it actually is.

I will of coarse send you the results of my queries.

Regards Ken.

[IanS]

By the time a fuse blows the semi conductors in the electroincs of the ECU are well dead.

fuses blow in 10s to 100s of milliseconds.

semiconductors blow in microseconds (or faster), there are far better ways of protecting ECUs than fuses and have been for many years.

The development early ECUs managed this well before they were let on the normal market.

Tanker safety is something I know little about but can realise that getting it wrong will cause a serious accident.

I have yet to see a car set up like this and suspect that the requirement for periodic detailed test would make it a non starter as a regulation.

There is a very large diference between 60 liters in a car and 35000 liters in a tanker as a source of danger

[Guest 2b cruising]

Yes Ian, I get and do not doubt what you are saying, but the fact is, the fuse is ther, and it is blowing.

If the people that fitted the new dash did not put it in then I guess I will never find out why.

I don't mind fitting a direct earth strap, but I find this set up very mystical, and difficult to understand.

My electrics and electronics is so very poor, I have always shied away from it. Hence me getting the pros to do the dash change.

Just like the fuse, the end price was mind blowing to.

[speedtripledan]

Next time you need a dash wiring my prices are far less shocking

[Guest 2b cruising]

And better workmanship.

So far I can only see 3 of the 6 gauges.

They still owe me boost gauge. Thankfull that is wired ready.

[fry61]

This fault sounds just like a main earth is missing & the fuse blowing is the return current trying to find a route back to the negative side of the battery; but why oh why is there a fuse in the return of any circuit on your car?

What does/does not work with this fuse blown/or removed from holder?

Did you need the jump lead to supply positive feed to starter or to earth the engine?

Tankers & aircraft need grounding when filling/discharging fuel as a static charge can be produced by the fuel flowing through the delivery hoses, is also possible with gas & powder flow.

Edited July 21, 2015 by florin metal works

[Longboarder]

I think you need to do some work clearly identifying this 'earth' wire to determine exactly what it is. Where does it come from and go to? How big is it? Is it one of the wires from the ignition switch to the solenoid or battery to ignition switch? Can't think of anything else you should have behind the dash with an inline 25A fuse. As a matter of course I always advise triple earthing battery to chassis to engine. I mean a big fat earth wire from engine to battery, another big fat wire from engine to chassis and another from chassis to battery. This is risk free, safe and effective. And I can't ever remember putting a fuse in an earth wire.

 

Nigel

[Guest 2b cruising]

Thank you Nigel.

The jump lead was used to supply earth.

I have traced one end of th wire where it is connected to the chassis.

I will dig my dash out this afternoon to trace its source.

If you say it should definately have a direct earth to engine and chassis, that is what it will get.

[Longboarder]

Doesn't have to be but it's good practice. That way earths have two big routes back to the battery. If one connection degrades and can't carry the current there is always a built in high capacity alternative so you get fewer earthing faults. It may well be that one of the terminals in your present set-up has developed some resistance through corrosion and part of the starter current is having to find other ways back to the battery negative.

 

Nigel

Edited July 21, 2015 by Longboarder

[Guest 2b cruising]

Hi to all and thanks for the varied and useful tips and information from you all.

Nigel, it would mean a major strip out to trace the fused earth wire, so after it leaves the chassis and goes through the fuse, I think that it goes to the start solenoid.

Ther was no earth cable from battery to engine, just the one from battery to chassis.

The cable runs from the battery, under the fuse box, then reappears through the hole in the bulkhead and then joining the chassis.

I have now fitted a new earth cable, battery size, between the battery to the engine block reasonably close to the starter motor.

Once again thanks to all for making things more interesting on one of my pet hate subjects.

Edited July 21, 2015 by 2b cruising

[Guest peter2b2002]

there was some else had problems starting turnd out the only earth was through the throttle cable

peter2b