Gt6 Mk1 repeatedly blowing fuse - it's back

[Peter Truman]

Colin I feel for you the frustration! the fact all was OK for 40 miles then the issue re-occurred, had you activated the O/D in that 40 miles? 

I know its illogical as independently reverse works but as the reverse power source is the common supply, have you isolated the reverse supply at its incoming supply at the reverse switch on the gearbox so the O/D is the only active circuit on that supply, then see if it still blows the fuse. I know it doesn't make sense BUT at this point I'd try anything!

Thinking out loud what would happen if the reverse light was on all the time ie switch failed and circuit to earth via reverse bulb then you activated the overdrive switch via gate 3/4 would that common source already be earthed? it shouldn't be a problem till the column switch is closed and provides power! sorry just thinking out loud its doing my head in & that's not hard at the moment when you've been in isolation/lock down effectively since March!

Otherwise as Non Member says isolate the new column switch at its bullets again and see if it blows or even wire in a loose hanging separate switch and see if all is OK.

[Colin Lindsay]

Overdrive worked perfectly for two days, including the long run down the dual carriageway and the motorway with overdrive on. No problems; instant engagement and disengagement. 

It only started to blow on a very hilly mountain road, with overdrive off, but once it started it was very frequent. I even had the fuse box hanging free over the battery to make sure it was not shorting out against the bodywork. With the circuit disconnected at the bulkhead it did not blow again. 

Will try both those solutions (means taking off my nice new tunnel cover and disturbing the seals, which was the best fit I'd ever achieved in any car) but will have to wait for more fuses.

James Paddocks are 35p per fuse, Rimmers are £2.35 per fuse... so yesterday's run could have cost me either £4.55, or a whopping £30.55...

Monday morning, strip the entire car out, and start again. Not until. Today I'll just pretend that I don't own one. Anyone want to swap for a Vitesse convertible?

[dougbgt6]

38 minutes ago, Colin Lindsay said:

James Paddocks are 35p per fuse, Rimmers are £2.35 per fuse... so yesterday's run could have cost me either £4.55, or a whopping £30.55...

You could buy a blade fuse box for that, then a box of 120 assorted fuses costs £4.65. 

You know you want to. 

Doug

[Colin Lindsay]

8 minutes ago, dougbgt6 said:

You could buy a blade fuse box for that, then a box of 120 assorted fuses costs £4.65. 

You know you want to. 

Doug

That's now definitely on the plans, but first thing is to get the car running. I'm going to put a modern fuse box in behind the glove box, on the inside.

I can't have a system where one fuse leaves me minus the essentials of wipers, brake lights, heater blower, reversing lights, temperature and fuel gauges, and indicators all in one. If the overdrive goes - fine - but I can't have it taking everything else with it. Thankfully the lights are on a different fuse but yesterday's heavy rain was worrying when everything else failed. I've to talk to a spark tomorrow, if I can track him down, and see if he can advise.

I've been wondering - despite telling myself not to, for today at least! - if the overdrive circuit appears on the bulkhead out of the main loom, and is powered from the top fuse, does the fault lie in that short section in between? It's a new Autosparks loom that I fitted in 2005, but there may be something going on in that foot or so of cable. I can't see any exterior damage but I'll maybe split the covering and inspect the wiring underneath.

[Pete Lewis]

or a cut down 6" nail   !!!!!!!!!!!!!

the smoke will locate the geographic location 

Pete

[dougbgt6]

Colin,

This is what a lot of us have installed, a direct replacement for the 3 fuse box. Easier to do than originally imagined, due to the red, purple, green grouping of the loom wiring

https://www.12voltplanet.co.uk/waterproof-panel-mounted-standard-blade-fuse-box-with-leds-10-way.html

A couple of threads on here show nicely how to do it, here's Adrian's

db

[Colin Lindsay]

Oh Lord... did you see THIS post in that thread???  I certainly made up for that... Having said that, the last few posts show the start of my fuse-blowing shenanigans... and six months on I'm still no further with determining the cause.

I've read that entire thread and even back then I was interested in replacing the fusebox - although now I'm still in two minds as to making the new fuse box the sole box, or keeping the old one as a dummy and have the replacement in behind, accessible via the footwell - intending to attach the spades from the back rather than the side, but the bits about bus bars put me off... hence seeking advice from a spark mate just so I can do a proper job. Does anyone have good photos of how their finished article was connected at the rear? 

 

 

[NonMember]

1 hour ago, Colin Lindsay said:

I've been wondering -

DON'T!!

Far too many people approach car electrics with a "poke-and-stab" guesswork. That's really really NOT the way to do it. You need a logical, analytical method. Do the check of the column bullets first, like I said in my last reply. If the fuse doesn't blow with the column switch disconnected then there is no point whatever in fiddling with the gearbox or taking the cover back off.

If I were to guess, based on all the previous evidence, I'd say you probably have something loose inside your steering column cowl. When first reassembled it was fine but after a bit of a drive - particularly on twisty bits or with lots of indicators or OD in/out - the loose bit has shifted such that it touches the OD wiring.

[Badwolf]

Colin - When I did mine I think that I posted a photo of the back. Not got the time at the moment to go through my whole thread (I really must spend some time printing it out for reference - it was never intended to get that long!!), but if I can do it, so can you. Get a box ordered, might be cheaper via fleabay, and get on with it. Its a simple but fiddly and oh so worthwhile job.

[Colin Lindsay]

10 minutes ago, NonMember said:

You need a logical, analytical method. Do the check of the column bullets first, like I said in my last reply. If the fuse doesn't blow with the column switch disconnected then there is no point whatever in fiddling with the gearbox or taking the cover back off.

The column switch is just a break in a loop, Rob - power comes from the reversing light switch / circuit, goes to the inhibitor switch, through the column switch, and back to the solenoid and earth. Just one big loop.

All the switch does is break the circuit. I haven't disconnected the column switch; just the entire circuit where it joins the main loom. I reckon if I bypass the column switch, so that the overdrive is permanently on when in 3rd or 4th, it'll still blow - but I'll certainly try it. Even if the switch bullets touch each other during driving, and they're hanging lower than all the other bullets so way down the column, they'll merely power the system up; they're also far enough away from anything so as not to make contact with anything metal. No exposed wires or incorrectly fitted bullets, and it's all insulated from when I fitted the new switch.

[Pete Lewis]

rather than keep blowing fuses while searching the culprit  by pass( remove ) the fuse with a 21watt bulb  if it lights you have a short if it barely glows you havnt 

if you convert to blades i have a load of resetable blade fuses 

Pete

[dougbgt6]

Buss bars:

The fuses split nicely into 3, 3 and 4 new fuses. The tops of these groups have to be connected. A lot of current flows through these connections and some thought buss bars the best solution. They aren’t, it’s overkill. 

I wrapped a heavy single core copper wires around the base of the connectors and soldered them in. 

I think Bad Wolf and I discussed the capacity of the single core and thought 27amp sufficient. 

Doug

 

[Badwolf]

Thats right Doug. I think I used  several strands of solid copper wired and twisted them around the rear connectors where needed and then over-soldered them to the connectors at the back. It wasn't a pretty job but it takes the load. I then insulated it, just in case something touched the back of the box via the glove box inside

[Badwolf]

Colin - Here you are...

https://forum.tssc.org.uk/topic/2623-the-delorean-style-bonnet-with-similar-hardtop-nose-to-tail-1972-spitfire-mkiv-restoration-upgrades/?page=32

Pete - I didn't know you could get re-settable blade fuses... and you have some...hhhmmm....and headlining..... hhmmm... have you thought of taking over the club shop and why don't they stock stuff like this... and the fuse boxes as a complete kit?

 

[Pete Lewis]

i will have to look them out , ratings are lower as orig were truck at 24v  so at 12v you need double the rating  ...i think   

when bored i will make up a list 

Pete

[johny]

Dont think thats right Pete, if you want to limit the current flow (Amps) to a component it doesnt matter what voltage that component is operating at as the power required to trip the breaker or blow the fuse is: 

Current x (resistance of fuse or breaker) squared.

As the resistance shouldnt change it just down to the amps...

[Badwolf]

Pete - Maybe you should start a listing of stuff that you want to shift. I'm sure that many members would be very grateful for what you have plus, you get to use the space. It won't be like fleabay, you just list the item price plus postage and delete them as they get sold.  "When bored".... if ever??

[Colin Lindsay]

I think I've found it. I think, and fervently hope - it's the most unlikely combination of things - the solenoid was a red herring, only stuck in place from disuse over the 18 months that the car was off-road, and not the fault. The two bullet connectors that I disconnected yesterday to isolate the overdrive are on the bulkhead, and connected by two cable ties to the main loom so that they can't move about. Running very close to them is the main brake line. When I disconnected the bullet connectors I wound them round the loom to keep them from touching metalwork and shorting out, but when I reconnected them today I found that one of the bullet connectors was loose and able to move by a quarter of an inch in and out of the connecting tube. At rest there's no problem, but I suspect either the bumpy roads, or the blast from the engine fan, has moved them into reach of the braided engine earth cable, which the loom was resting on, (it's the long y-shaped one from a later Spitfire) and they've shorted out against that, or possibly the wet weather yesterday allowed water to short it out. Either way I suspect that there's been a short when conditions permitted the bullet connector to both pull out of the tube and touch metalwork. I'll confirm once I can get sufficient fuses to play about with.

I'm still on for replacing the fusebox, but if this is the problem then I'm more than halfway to combatting it.

[NonMember]

4 hours ago, Colin Lindsay said:

The column switch is just a break in a loop, Rob - power comes from the reversing light switch / circuit, goes to the inhibitor switch, through the column switch, and back to the solenoid and earth. Just one big loop.

All the switch does is break the circuit.

Yes, I know! I'm actually an electronic engineer part time (when I'm not doing software). The circuit goes from the fuse to the inhibitor switch, to the column switch, to the solenoid. Closing the inhibitor switch blows to fuse which means there's a short to earth BETWEEN THE INHIBITOR AND THE COLUMN switch. Anything the other side of the column switch would not blow the fuse until you turn that switch on. Anything the other side of the inhibitor switch would blow it before you get to 3rd gear. At one point earlier in the saga you said you'd disconnected the bullets on the column and not had fuse blowing. One of these splits the wire from the inhibitor to the column switch - so that test shows the problem to be on the column side of those bullets. I asked you to re-do that test to confirm whether it was real or a red herring.

Anyway, I see you've found something. With luck, the problem you found with the bullet near the bulkhead (presumably the one from the inhibitor to the column?) will prove to be the cause.

[dougbgt6]

58 minutes ago, johny said:

Dont think thats right Pete, if you want to limit the current flow (Amps) to a component it doesnt matter what voltage that component is operating at as the power required to trip the breaker or blow the fuse is: 

Current x (resistance of fuse or breaker) squared.

As the resistance shouldnt change it just down to the amps...

Johny,

power does not trip the breaker. Current and current alone trips the breaker.

Power is not (current x resistance) squared. It is (current squared x resistance) 

You are correct that dropping the voltage over the same resistance will drop the current.

I’m sorry to point these things out, but you mess with volts and amps at your peril!

Doug

 

[johny]

I think youll find we're in agreement as for the formula👍 However it must be power that operates the fuse or breaker as either has a small resistance so with the current flow is consuming power. In the fuse this power is heat that melts the metal to disconnect the circuit....

[Colin Lindsay]

3 hours ago, NonMember said:

I asked you to re-do that test to confirm whether it was real or a red herring.

That's very appreciated, as always, but by the time I read the post I already had the system disconnected and largely dismantled so it's probably my fault for marching on ahead and starting before reading the instructions... ah well.

[johny]

3 hours ago, dougbgt6 said:

Johny,

power does not trip the breaker. Current and current alone trips the breaker.

Power is not (current x resistance) squared. It is (current squared x resistance) 

You are correct that dropping the voltage over the same resistance will drop the current.

I’m sorry to point these things out, but you mess with volts and amps at your peril!

Doug

 

oops yes Doug I see now I got the squared in the wrong place it is indeed  I x I x R  however the effect it has in operating the fuse/trip is the same....

[Peter Truman]

why not use P=V*I, simpler, 60 watt power at 12v = 5amp. 

[johny]

well we're talking about the power needed to operate the fuse/trip so you could use P=VI but the voltage would have to be that dropped across the fuse/trip (mV?) not the circuit supply voltage.