Spark from Fuel gauge, no longer working

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Andymoor94
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Spark from Fuel gauge, no longer working

Postby Andymoor94 » Tue Feb 04, 2020 9:03 am

Good morning guys!

1954 split screen Mog

So on my commute today, a worrying sight occurred. A small spark shot out from under my fuel gauge towards my leg, and now my fuel gauge is not moving whatsoever, ignition on or off.

Backstory: bought the car with a stuck sender, figured that out from earthing the cable from the sender. Took sender out, unstuck it, worked like a charm. But upon reinstalling the instrument panel, I did notice that only one bolt was holding the panel on to begin with (of the two underneath), so I found a spare bolt from a box of bits and popped that in for now. I foolishly did not inspect the wires before reinstalling.

Now I'm at work until 5pm, hence the forum message, I don't have the means to look at the issue right now, but I would like to know a bit more about what could have caused the spark?

My thoughts:
Corroded wire shorted on the foreign bolt I installed?
There is a loose green wire behind the dash, dangling onto the parcel shelf. The end was exposed, yet glued to some card. Could that have come into contact with my starting handle (That I keep on on the shelf) or worse, could that have come loose during the drive? I need to investigate what that wire is, really!

Any thoughts will better prepare me for the evening ahead where yet again, I have to postpone my evening to fix something!
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simmitc
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Re: Spark from Fuel gauge, no longer working

Postby simmitc » Tue Feb 04, 2020 10:31 am

As standard, your car would have been positive earth, but many have been converted to negative. I mention this because a green wire is usually the opposite from earth, but without knowing your car, I can;t say whether it will be +ve or -ve, but if it came loose then it could cause a spark if it touched the body. If the starting handle is not earthed, then that cannot cause a spark, even if you attached the green wire to it.

You really need to look behind the gauge to see what's happened. It could be a loose wire or the gauge unit failing. You can drive without a working gauge, but need to ensure that there are no loose wires that could cause a fire - and also be confident about how much petrol is in the tank!

Andymoor94
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Re: Spark from Fuel gauge, no longer working

Postby Andymoor94 » Tue Feb 04, 2020 10:35 am

simmitc wrote:
Tue Feb 04, 2020 10:31 am
As standard, your car would have been positive earth, but many have been converted to negative. I mention this because a green wire is usually the opposite from earth, but without knowing your car, I can;t say whether it will be +ve or -ve, but if it came loose then it could cause a spark if it touched the body. If the starting handle is not earthed, then that cannot cause a spark, even if you attached the green wire to it.

You really need to look behind the gauge to see what's happened. It could be a loose wire or the gauge unit failing. You can drive without a working gauge, but need to ensure that there are no loose wires that could cause a fire - and also be confident about how much petrol is in the tank!
Well the good news is I just took it for a drive to find the wipers and trafficators aren't working now either, which narrows it down a bit (funny enough)
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Re: Spark from Fuel gauge, no longer working

Postby ManyMinors » Tue Feb 04, 2020 11:33 am

All those things are on the same fuse of course so probably the fuse has blown - BUT it must have blown for a reason - probably the short which you saw as a spark and possibly caused by that loose wire. To get home I would at least tape up the exposed end of that wire and investigate what it is attached to asap. The wires to the fuel gauge are green for a start. Dodgy wiring in old cars is one of the biggest headaches!

Murrayminor
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Re: Spark from Fuel gauge, no longer working

Postby Murrayminor » Tue Feb 04, 2020 1:31 pm

The first check would be to ascertain if the wire could have reached earth or another metal surface, such as your starting handle.
Secondly the glued end of the wire could have been placed there as a method of preventing the wire from touching metal in an attempt to insulate it.
The next course of action would be to insulate the stray wire and then try trace it to where it begins.

Once you have identified the wire it should be fairly easy to repair.

I say fairly easy, but I hate working on electrics :D
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oliver90owner
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Re: Spark from Fuel gauge, no longer working

Postby oliver90owner » Wed Feb 05, 2020 1:10 pm

Do start with checking that wire for battery potential when you eventually feel it safe to replace the fuse. If there is no volts on it, it likely did not cause your fault. If there is battery voltage, it is likely, but not necessarily, the cause of the problem. All bare ends of wires should be secured with tape and held firmly.

Andymoor94
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Re: Spark from Fuel gauge, no longer working

Postby Andymoor94 » Mon Feb 10, 2020 9:01 am

Murrayminor wrote:
Tue Feb 04, 2020 1:31 pm
The first check would be to ascertain if the wire could have reached earth or another metal surface, such as your starting handle.
Secondly the glued end of the wire could have been placed there as a method of preventing the wire from touching metal in an attempt to insulate it.
The next course of action would be to insulate the stray wire and then try trace it to where it begins.

Once you have identified the wire it should be fairly easy to repair.

I say fairly easy, but I hate working on electrics :D
I'm not seeing the fun side of electrics yet either! I did some looking around and found the following:

- The green exposed wire was from some aftermarket electrical windscreen washer pump. I've disconnected the entire thing and installed the usual hand pump. Did not fix the electrical issue.
- I noticed what looked like a brake cable coming from the offside trafficator - I presume this must be the earth, judging by the mirror image on the nearside. I screwed that into the dash. No luck, however thinking about it as I write this, the dash is obviously painted, so that could affect the grounding.
- The joyous green corrosion from a variety of under-bonnet wires! The fuse "box" and regulator are riddled with green copper wire. I think a session with clippers and strippers (Of the electrical type, naughty boy!) are in order. I can see a few bits of cable where the braided sheath has worn, so I'll try contain that.

Have yet to see if the brake switch could have cause the issue, which I've heard is a common failure
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simmitc
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Re: Spark from Fuel gauge, no longer working

Postby simmitc » Mon Feb 10, 2020 9:37 am

I noticed what looked like a brake cable coming from the offside trafficator
??? :o
The brake light switch is a common failure, but it only stops working, not usual for it to short to earth - very limited potential for that to happen.
The highly corroded fuse box is not going to help matters. You could try removing all the wires from the "out" side of the fuse, replace the fuse with a low rated one (say 5 amp, that should be enough for each individual circuit), and then reconnect the circuitas one by one, testing each, until you find which one causes the fuse to blow.

myoldjalopy
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Re: Spark from Fuel gauge, no longer working

Postby myoldjalopy » Mon Feb 10, 2020 9:46 am

That 'brake cable coming from the trafficator' is probably the tensioning wire for the headlining - assuming you have a four-door model. The trafficators earth simply through being screwed to the body.

Andymoor94
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Re: Spark from Fuel gauge, no longer working

Postby Andymoor94 » Mon Feb 10, 2020 11:32 am

simmitc wrote:
Mon Feb 10, 2020 9:37 am
I noticed what looked like a brake cable coming from the offside trafficator
??? :o
The brake light switch is a common failure, but it only stops working, not usual for it to short to earth - very limited potential for that to happen.
The highly corroded fuse box is not going to help matters. You could try removing all the wires from the "out" side of the fuse, replace the fuse with a low rated one (say 5 amp, that should be enough for each individual circuit), and then reconnect the circuitas one by one, testing each, until you find which one causes the fuse to blow.
Next call is to remove and clean the wires, ensure all connections are good and just sleeve any bits of frayed sheath. It's all very new to me, so which side is "out"? I presume that's the wire heading to the component, not to the battery?
myoldjalopy wrote:
Mon Feb 10, 2020 9:46 am
That 'brake cable coming from the trafficator' is probably the tensioning wire for the headlining - assuming you have a four-door model. The trafficators earth simply through being screwed to the body.
Ah ok. Yes 4 door model. Well at least I know what that could be then. The end of the cable was screwed into the top of the trafficator, hence the presumption!
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simmitc
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Re: Spark from Fuel gauge, no longer working

Postby simmitc » Mon Feb 10, 2020 2:01 pm

Yes, "out" towards the components. One problem with old cars is not knowing what might have been changed over the years, so a multimeter is a really useful tool. With the fuse removed and the ignition on, check for 12 volts on the terminals. One set, the "in" will have 12v whilst the "out" will have 0v. On the multimeter, select a scale such as 0-15v DC and then hold the red wire to the battery +ve and the black wire to the fusebox terminal.

Most workshop manuals will have wiring diagrams in them, and those are really helpful to understand what should go where, and which circuits are fused (such as wipers, fuel gauge and trafficators) and which are not, such as fuel pump, horn, headlights.

Andymoor94
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Re: Spark from Fuel gauge, no longer working

Postby Andymoor94 » Tue Feb 11, 2020 4:11 pm

simmitc wrote:
Mon Feb 10, 2020 2:01 pm
Yes, "out" towards the components. One problem with old cars is not knowing what might have been changed over the years, so a multimeter is a really useful tool. With the fuse removed and the ignition on, check for 12 volts on the terminals. One set, the "in" will have 12v whilst the "out" will have 0v. On the multimeter, select a scale such as 0-15v DC and then hold the red wire to the battery +ve and the black wire to the fusebox terminal.

Most workshop manuals will have wiring diagrams in them, and those are really helpful to understand what should go where, and which circuits are fused (such as wipers, fuel gauge and trafficators) and which are not, such as fuel pump, horn, headlights.
Good news, I removed all wires from the fuse box and trimmed them back, cleaned out the connections/ports and replaced a ratted wire connecting ground. Popped in a 25amp fuse, she started up and everything seems to be running. I tested all of the aforementioned parts and all seem to be working (Minus the usual trafficators are stuck problem). I have a drive to the shop today after work, so I should hopefully be able to test on the road. Fingers crossed.

Thanks for the help and ideas
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