Fuse Keeps Blowing

[kevin the chicken]

Hi,

Electrics, my favourite subject. I have an intermittent and annoying niggle at the moment. The fuse that protects the Tacho, speedo and the indicators keeps blowing on occasion. It is a 10amp one, is this sufficient for these circuits? Everything works fine for long periods of time and then suddenly it blows again. I havent really noticed when it has blown exactly before but the last time it happened it was when I was overtaking and flipped the indicators on (I noticed because I stopped almost straight away after and the speedo was stuck at 70)

Got home and popped a new fuse in, turned the igniton on and the speedo returned to zero and indicators were working again. The tacho doesn't work anyway, could this be relevant?

The indicators are operated by a rocker switch which was replaced a few weeks ago because it had a loose terminal on the back and I think the relay was a new one when the car was rewired earlier this.

Where should I start my futile search first? I was so sure that is was going to be that switch.

 

Regards

Kevin

[fry61]

Can you see the part of the fuse that's blown? does it look like it has just melted a small section or is it completely missing? Small gap probably equals overload; large gap maybe dead short. If a small gap I would try a 15amp fuse & see if that holds on any longer, if it blows in the same time-scale look for a wiring fault.

[Longboarder]

I would start by disconnecting the tacho and tying back their wires having insulated their ends. Remove the fuse that blows and take a spade connector from the live side of the fuse socket to two 10 amp inline fuses. Connect one with a new wire to the speedo and connect the other to the indicator relay terminal 49 thus bypassing all of the possibly suspect supply wiring. Now drive and wait and see what happens. Any fuse blowing would suggest the problem is further along the wiring and would prove the supply side which can be reinstated but at that stage you would know which circuit was implicated. If no fuse blows then it's in the supply side (unlikely) or the tacho(could be shorting and that with the load of indicators and speedo as you have at the present might just be enough to blow a 10amp fuse).

 

 

Nigel

[kevin the chicken]

I did have a good look at the fuse and it was hard to see the missing piece, in fact with the absence of my reading glasses I had to employ a magnifying glass!

[Guest Alan_builder]

Don't think you can tell diddly squat at the moment.

 

I know what Florin is saying about fuses "sagging" nearly got the wrong word.

I would not do that just yet.

 

I gave up with Longborder's post, normally Nigel is on the money.

 

What I would suggest is to do some temporary wiring. Wire a 20A ammeter in series with a 10A fuse in place of the fuse which blows from time to time. Now if the ammeter is the right way round or a center zero meter you can read the current flowing in the fuse.

 

A 10A fuse will blow between 7A and 13A if you are lucky (depends on the type of fuse, the load characteristics and other factors). The way it fails (blows) Florin has described.

 

So you need to see what the current is in each circuit and the total. The indicators will take between 5A and 7A, all depending on bulbs / lamps and the system and the battery voltage. So exercise the indicators last.

 

If your standing current is below 10A just replace the fuse and look for a short. If the current is 9A to 15A then upgrade the fuse as Florin says. If you have bent the needle on your ammeter look for a short.

 

What you most probably have is a short, an intermittent short, The wiring in an indicator light or chaffing on the wire. May be wiring to the speedometer or any other item.

[tractor]

hi kevin I had the same problem turned out to be where the wiring came through from steering wheel it had rubbed on chassis and had worn through I had given up looking for it then I was doing something else on the car and I spotted it . wiring wot a pain

[speedtripledan]

Get one of these http://www.ebay.co.uk/itm/DRAPER-43060-ACT2-3MM-CAR-FUSE-CURRENT-BLADE-AMP-TESTER-/380311803318?pt=UK_Diagnostic_Tools_Equipment&hash=item588c5995b6

that way you can test the load on that circuit, that way you will know if the fuse rating is correct, failing that bring it here and i will look at it for you

[Longboarder]

Handy piece of kit that for lots of things although not much help in this case where you already know that circuit intermittently draws more than 10 amps and you don't know why and it won't tell you why. I have just bought one after seeing the link.

 

Nigel

[speedtripledan]

Handy piece of kit that for lots of things although not much help in this case where you already know that circuit intermittently draws more than 10 amps and you don't know why and it won't tell you why. I have just bought one after seeing the link.

 

Nigel

I use one to determine loads on new circuits when I rewire cars

[kevin the chicken]

Damn you lot! I've just bought one too. Thanks for your help, it's given me a bit more understanding of what goes on. I'll try either fixing or isolating the tacho first to see if that makes any difference. At least I know it wont be a worn through wire as it was all replaced earlier this year and I have not done many miles in it since then for one reason or another. I had thought of separating the circuits on their own fuses but not as easily as Longboarder suggested so I may follow that idea (hadnt thought of plugging directly into the fuse box).

I'll keep you posted

Kevin

[Guest peter2b2002]

handy bit of kit , another one on order

peter2b

[kevin the chicken]

Just got my car back from a local garage where I took it to try to resolve some of my electrical problems. They started off by replacing the connections on the coil which I knew were dodgy, couldn't get any of the proper plugs so they made some up using new pins and other odds and sods which looks neat enough.

The end result is the tachometer now works which is a result and now its just a matter of putting a few miles on the car to see if the fuse blowing problem is gone but it is another small step forward and now everything on the car works!