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Thread: Fuse, She Blows

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    Fuse, She Blows

    I have a circuit which keeps blowing the fuse. Not immediately, but after a short amount of driving, like it did today. It's the second fuse from the top inside the engine bay box, and it takes out the turn signals, a couple of gauges and lights and other stuff too I'm sure. Question is, how do I track down the culprit? I'm suspecting it's related to the turn signals, just a guess, but I did do some work on the tailights somewhat recently. And when I looked down today and noticed the gauges were out again, I had been sitting a light with my right signal on for a minute or two.

    Help, oh Triumph Overbrain!
    Martin
    '72 TR6

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    Re: Fuse, She Blows

    That sounds like the fuse for the 'green wires' circuits.
    You should have a schematic.
    http://www.advanceautowire.com/schematics.htm
    DRIVE 'EM IF YOU GOT 'EM

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    Re: Fuse, She Blows

    There are a few ways to find your problem. If you feel it is in the signals switch. that would be easy don't use it NO No! is it left or right? all the wires travel under the steering column Light green is com. green and white right turn green and red left turn that would be first test . All these wires are hot or would be if turn sig is on. The column has a cover over wires first place to look. With the turn sig on bang the steering wheel left then right. ( NOTE to save fuses make a jumper with a lite socket and bulb. and put across the fuse pinch wires in with fuse to hold wires. fuse good or bad no matter ) The light will glow if short is made You should be able to see lite while banging wheel. CAUTION do not over size fuse. If you have only worked in the boot and find that it is say only left turn and you have the covers on remove and check same. All wires come from the drivers side so the right side is most likely OK. All wires run next to the drivers seat along door sill. If a wire is pinched it could be years for a problem to show. Work on seats carpet any thing on drivers side ?? Under the dash is more work wires either go to rear of car or inst. or from the fuse box. If you added a new radio look there and at gauges. If a gauge light has fall out it could be banging around under dash. It is not likely a side lights have a ground. Madflyer

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    Re: Fuse, She Blows

    Thanks Madflyer. I like the light bulb idea. I'm just guessing it's associated with the right turn signal, which is what I was using last time out when I noticed the fuse had gone out. The strange thing to my little electrical mind is that all the signals and lights work as they should when the fuse is not blown. Is that normal?
    Martin
    '72 TR6

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    Re: Fuse, She Blows

    If I were doing this, I'd remove the fuse in question and connect a high-value ammeter. Then watch it as you turn things on and off, jiggle wires, and so on. Watch for a current that is close to or above the fuse's current rating. It's likely that something, somewhere, is making a momentary short circuit, because of a loose connection or damaged wire.
    Steve Maas
    1966 Triumph TR4A, undergoing restoration: http://www.nonlintec.com/tr4a
    1952 MG TD, restoration completed 2014, sold 2016: http://www.nonlintec.com/mgtd
    1960 Austin-Healey "Bugeye" Sprite, sold 2010: http://www.nonlintec.com/sprite
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    Re: Fuse, She Blows

    Actually I think I found the problem. What amp rating are these fuses supposed to have? Should they all be 35, or are they different ratings for different circuits.
    Because in my fuse box I have 20, 30 and 35 amp fuses. The 20 amps are the replacements I've been using. (Thankfully in 20+ years of owning this care I have had almost no electrical issues. Of course 'those Lucas electrical problems' are the first thing quasi-knowledgeable people say to me when they learn about my TR6, but it's just never been an issue for me).

    Point is - the fuse that's been blowing is on the circuit to which I added an electric puller fan recently, and I've been using a 20amp fuse there. So I'm going to up rate it to 35amps. I presume the circuit's been blowing when the fan kicks in for very long. Add a turn signal to the fan's draw and boom, probably out goes the fuse. Don't we think?
    Martin
    '72 TR6

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    Re: Fuse, She Blows

    Probably should wire a circuit just for the fan instead of overloading the wire for the 20W. Don't need a fire in the baby.
    Larry K
    58 Jag 3.4 MK 1 auto under restoration, 57 Jag 3.4 MK1 manual (parts car),
    03 Cooper S, 2011 Cooper S Countryman, 2011 Land Rover LR4 HSE LUX, 1964 Valiant V200
    Also had , 68 Cortina 1600E, 64 Spit 4 & 80 1500, 73 GT6 3, 71 XJ6, 79 XJ6, 86 XJS V-12, 53 XK120 OTS.

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    Re: Fuse, She Blows

    Martin The horn has the larges value fuse I think 20 A. The rest are 1/2 that value. The addition of any electric item fans fog lights etc. should be on new circuit and run by a relay. I removed the glass fuse holder and went to a new blade style fuse and also split my circuits and now have room for 5 circuits one is a spare. also the blade fuses have ones that glow when blown and are easy to read value and color too. If you are still running the Lucas Alt it is only 43 Amps. So lights on, fan on, turn sig on, radio on that adds up quickly. Many have gone to 63 Alt easy to do. I also added a Sig. lighter straight from battery with it's own in line fuse for a USB plug for my TOM TOM GPS. Are cars were built at an earlier time and may not have even been driven at night or rain fans, heated seats, lights, amps for radios were never in UK thinking. All added items can be installed cleanly and or out of sight Items like LED lights in dash brake and tail lights will be brighter an less Amps. Remember size matters that includes wire and fuse. Madflyer

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    Re: Fuse, She Blows

    Not a Lucas alternator, that one gave up the ghost a few years ago. It's replacement is a Remy reman'd unit, rated at 55 amps. Just now learning that a Lucas '35A' fuse is actually something a bit more than 20amps, correct? That's the fuse I moved to the fan circuit for now and it seems to be holding.

    I appreciate the suggestion to move the fan to its own circuit; I'll work on that. I also understand that Dan Masters suggests that the 'red' circuit (bottom fuse) ought to have a 10amp(AGC) fuse, the purple 15amps, and 20 for the white. I'll be doing that too. Thanks folks.
    Last edited by Martin Secrest; 08-03-2020 at 08:27 AM.
    Martin
    '72 TR6

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    Re: Fuse, She Blows

    You are right UK Amps are not the same as US Amps I was told no fuses bigger than 20 Amps on Brown White and Green com. Madflyer

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    Re: Fuse, She Blows

    Quote Originally Posted by Martin Secrest View Post
    ... Just now learning that a Lucas '35A' fuse is actually something a bit more than 20amps, correct? That's the fuse I moved to the fan circuit for now and it seems to be holding.
    In a word, yes. The old British rating was the current that would blow the fuse "instantaneously," which I presume means a small fraction of a second. Today, fuses are rated at the highest current where they are guaranteed not to blow. There is about a 2:1 difference, so today's 20A fuse is more like a 35A one per the British spec. Dunno if the TR6 used the old British standard, or the more modern one.

    I thought of this, but I figured you used, say, a 35A modern fuse, and that would be more like a 70A British one. But if you used a 35A Lucas fuse, and it was rated per the old British standard, then, yes, that might be the whole problem.

    BTW, I have a treatise on this subject at http://sprite.nonlintec.com/electrical/
    Steve Maas
    1966 Triumph TR4A, undergoing restoration: http://www.nonlintec.com/tr4a
    1952 MG TD, restoration completed 2014, sold 2016: http://www.nonlintec.com/mgtd
    1960 Austin-Healey "Bugeye" Sprite, sold 2010: http://www.nonlintec.com/sprite
    1967 Porsche 912: http://www.nonlintec.com/porsche

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    Re: Fuse, She Blows

    Actually the 35a Lucas fuse was holding - it was the fast blow 20A AGCs that were not. But at the suggestion of several here, I moved the power supply wire off the multi-circuit to a spare lug (jumpered) from the white side, and added a 20amp fast blow fuse in line. Easy enough. But I can't find out what the fan (Revotec from Rimmer Bros, they make a great kit for TR6) draws but hopefully not more than 20a at any time. I figure that with no other load on the circuit the fuse will hold, as it was before, at least until I turned on a blinker, LOL. Have yet to test drive the fan, and I can't do it today, we are getting socked with rain here in Virginia from Tropical Storm I Can't Pronounce You.
    Martin
    '72 TR6

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    Re: Fuse, She Blows

    Just saw something on Moss that says the Revotec fan draws about 8.5amps by itself. So presumably at startup, it's pulling sufficiently less than 20.
    Martin
    '72 TR6

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    Re: Fuse, She Blows

    Good call Martin most people do not think of that, starting current will draw much more than running. Across the board any device will do the same so slow blow are always a good call. In some electric circuits a compactor is use for just that reason like a soft start. Madflyer

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