Headlight circut melting fuses.

nlopitziii

nlopitziii

Joined
Feb 18, 2007
Messages
159
Age
47
Location
Canton, Ga
Bike
2004 ST1300
Headlight circuit melting fuses.

I'm having a problem with my headlight circuit, it keeps melting the fuse, not blowing it but melting it.

I have stock Honda bulbs in my headlight. I feel it might be bad connections at the fuse box terminals for the 20 amp headlight fuse. Can these be removed for cleaning?

If I remove the fuse there is about a 1 volt increase (i.e. 13.2 with fuse in, 14.5 with fuse out)

Be for I cut the fuse out and wire in an aftermarket fuse holder I would like to test the circuit.

I have a DMM but am not quite sure how to test this or what the norm would be. Any pointers?

Thanks All
 
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>If I remove the fuse there is about a 1 volt increase (i.e. 13.2 with fuse in, 14.5 with fuse out< snip

You mean there is a 1+v increase of the battery after the fuse is remove? Is this with the lights off or on?
If the lights are off then there's a short/drain some where in the line ... If the lights are on at a slower rpm you can easily see an increase in voltage due to lack of draw for the lights when fuse is pulled.
 
I recently grabbed the positive side on the fuse box to run my amplipher for the sound system. I keep blowing the fuse and dont have a headlight. However the amp still works because I'm on the plus side and have fused the amp inline.

Is it possible to put a 25-30amp fuse in there whithout any danger of overloading the circut?
 
In general I would not suggest putting a larger fuse than designed in the fuse block.
If you are pulling the power for the amp before the fuse maybe something else is going on. Oversize bulbs? Is this a power amp it would be a good idea to install a acc fuse block and run the power from the battery terminal to the fuse block. Run this thru a relay and pick the signal to trigger the relay from the acc circuit in the oem fuse panel on the left side of the bike. Red wire green stripe iirc.

As for melting the fuse if you mean the fuse body not the element in the fuse iow the plastic is melting I would suspect very dirty contacts for the fuse. Without delay I would clean the contacts and check for a secure connection. It's possible the fuse hold deformed.
If its the fuse connection causing the issue the fuse will not protect you!
 
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st1300r said:
As for melting the fuse if you mean the fuse body not the element in the fuse iow the plastic is melting I would suspect very dirty contacts for the fuse. Without delay I would clean the contacts and check for a secure connection. It's possible the fuse hold deformed.
If its the fuse connection causing the issue the fuse will not protect you!
Click to expand...

Exactly so! You must have a high resistance in the connection for it to generate heat. Especially in a circuit carrying higher current.
 
Re: Headlight circut melting fuses. 20A?

The headlights are supposed to fused at 10amps. Take a look at the attachment. If the 20amp fuse is blowing - you probably have a problem with some other component, not the headlight(s).

Good luck,

Dale
 

Attachments

  • ST 1300 fuses.jpg
    ST 1300 fuses.jpg
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Whoops, my bad!

I didn't realize that you were talking about an ST1100. I'm not familiar with their wiring.

Dale:cool:
 
I can't find anything to fit in the contacts that would clean them so I'm just going to cut the wires off at the fuse box and splice a spade fuse holder in. That way I'll have clean connections.

Good timing as the bike is down while waiting for front wheel bearings and new top box install.
 
I know this is a very old thread but I'm having same issue with a UK Police Spec 1996 Pan. Replacing the regular fuse with a new inline fuse, would it, does it solve the problem?
 
Skydivebash said:
I know this is a very old thread but I'm having same issue with a UK Police Spec 1996 Pan. Replacing the regular fuse with a new inline fuse, would it, does it solve the problem?
Click to expand...

If your same issue is the fuse body (plastic) is melting, then as said earlier, the contacts are probably dirty/corroded and the fuse to holder resistance is high, creating heat. Before I started cutting wires, I would do everything I could to inspect (with a magnifying glass) the existing fuse holder and try to clean it with a piece of sheet metal to which I had glued some very fine sandpaper. If all else failed, then, yes I'd consider another inline fuse.

The fuse is chosen to limit the current flow in a given wire. Different wire sizes and different insulation types get you different sized fuses. The resistance of the wire to current flow creates heat so more current = more heat. The old trick of yanking out a 15 amp fuse in a house's fusebox and putting in a 20, a 25, or even a 30 is a great way to eliminate the protection fuses provide. More than a few fires have started with this trick. If you do it on your bike, increased heat and a bit of vibration could melt or otherwise damage the insulation on that wire leading to a short. Murphy guarantees that this will happen in the most inaccessible part of the wiring harness. Enough heat could also damage adjacent wires.
 
SMSW said:
The fuse is chosen to limit the current flow in a given wire. Different wire sizes and different insulation types get you different sized fuses. The resistance of the wire to current flow creates heat so more current = more heat. The old trick of yanking out a 15 amp fuse in a house's fusebox and putting in a 20, a 25, or even a 30 is a great way to eliminate the protection fuses provide. More than a few fires have started with this trick. If you do it on your bike, increased heat and a bit of vibration could melt or otherwise damage the insulation on that wire leading to a short. Murphy guarantees that this will happen in the most inaccessible part of the wiring harness. Enough heat could also damage adjacent wires.
Click to expand...

I couldn't resist making a few comments, since I'm an old Navy ET and EE.

The wire AWG size , type of insulation, whether or not the wire is in a bundle, and ambient temperature determine the Maximum size fuse that can be used. But the size of fuse chosen should be based on the start-up or normal current draw of the load. Of course the fuse size should be less than the maximum ( based on the wire AWG size and the other previous mentioned factors ) , and a bit more than the normal current draw of the load. Another factor to consider ( for what wire size to use ) is the allowable voltage drop / loss between the source and load. With a car or motorcycle , on a high current circuit ( like a headlamp circuit ) , it's not uncommon to see a 1.0 to 1.5 volt loss between the source ( battery ) and headlamp. Some loss may be due to the "contact" resistance of a switch in the circuit, besides the IR drop in the wire, itself.

There is also a loss between the negative battery terminal and the "ground " at the headlamp. Sometimes, this drop in the ground "run" isn't checked or considered. To reduce this ground drop, an extra wire can be run from the ground connection at the load, to a conveniently close connection point on the chassis or engine.

I usually like to use a one size larger ( smaller AWG number ) wire than is required. That will help reduce the voltage drop.

By the way, marine grade wire is a good choice. For a given AWG, it will have the same cross sectional area, but has more strands ( each strand is smaller in diameter ) and the insulation is a better grade and oil resistant. It's more flexible and less prone to failure over time. The increase in cost is negligible.
 
SMSW said:
...I would do everything I could to inspect (with a magnifying glass) the existing fuse holder and try to clean it with a piece of sheet metal to which I had glued some very fine sandpaper.
Click to expand...
And to do so I'd remove the fuse box from the compartment (just unlatch it on the RHS) to inspect the backside, in particular check the crimped cable-ends for signs of overheating (my guess is the heat melting the fuse-cases origins from corrosion/increased resistance there)

The crimp-inserts for the fuse block are avail as after-market parts (don't have a US source at hand though), so repair by shorting/cutting damaged cable ends and placing a new crimp on is possible.

To prevent such from happening at all, annual removal/inspection of the rear side of the fuse-block/box and treatment with ACF-50 or similar seems advisable...
 
Jim Van said:
I couldn't resist making a few comments, since I'm an old Navy ET and EE.

The wire AWG size , type of insulation, whether or not the wire is in a bundle, and ambient temperature determine the Maximum size fuse that can be used. But the size of fuse chosen should be based on the start-up or normal current draw of the load. Of course the fuse size should be less than the maximum ( based on the wire AWG size and the other previous mentioned factors ) , and a bit more than the normal current draw of the load. Another factor to consider ( for what wire size to use ) is the allowable voltage drop / loss between the source and load. With a car or motorcycle , on a high current circuit ( like a headlamp circuit ) , it's not uncommon to see a 1.0 to 1.5 volt loss between the source ( battery ) and headlamp. Some loss may be due to the "contact" resistance of a switch in the circuit, besides the IR drop in the wire, itself.

There is also a loss between the negative battery terminal and the "ground " at the headlamp. Sometimes, this drop in the ground "run" isn't checked or considered. To reduce this ground drop, an extra wire can be run from the ground connection at the load, to a conveniently close connection point on the chassis or engine.

I usually like to use a one size larger ( smaller AWG number ) wire than is required. That will help reduce the voltage drop.

By the way, marine grade wire is a good choice. For a given AWG, it will have the same cross sectional area, but has more strands ( each strand is smaller in diameter ) and the insulation is a better grade and oil resistant. It's more flexible and less prone to failure over time. The increase in cost is negligible.
Click to expand...

Jim,
All good points. I would argue with you about the negligible cost increase because marine grade wire seems to be available from only a few sources online and in much larger quantities than is usually needed by us home mechanics. I'm an electrician, and standard THHN stranded wire is available either in 500' reels, or by the foot at big box stores (read Lowe's or Hopot). I found marine grade wire was much more expensive (as expected) at the local West Marine yacht store. Cheap wire, so called 'primary wire' from Advance and Auto Zone is stranded but has a lower temp rating and I've been told conflicting things about its resistance to oils and greases to really know the score with this stuff.

When I needed wire I bit the bullet and got the marine stuff from WM - I figured a failure in cheap wire would be much more expensive (on the road, at night, and in a rainstorm) than buying a couple of 100' rolls at the yacht store.
 
I would think that the most likely culprit for melting is not dirt but, loose contacts. it happens a lot to both types of fuse holders. the "inline fuses" use a really cheap spring to maintain contact with the fuse.. over time the spring looses it's tension. and the blade type fuse, uses the same contact as the crimp on wire terminals. they get looser with each time someone removes or installs a fuse. if a person gets into the routine of actually looking at the parts, and adjusting or fixing when working on these , a lot of these problems could be headed off, before they get so loose that melting results.
 
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I forget where I bought my last order of Marine grade wire, since it's been awhile.

I just did a quick search and BestBoatWire has a 25 ft. roll of 16 AWG for $3.50 and 14 AWG for $5.00 , not too bad. Those are the sizes I usually use.
 
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