View Full Version : fuse no 8 melting

campermans cave
04-25-2015, 01:02 PM
hi guys, im really stuck with this one, i recently aquired a 03 lwb sprinter which once i got home i realised that there were no dash lights, checked the fuse and it was blown so i changed it with the same rating. now when i turn on side lights the fuse melts! dosent blow just continiues to get so hot the plastic around the blade fuse drips away (if left long enough)
i have searched all the wiring for shorts, removed all bulbs (eg) number plate, marker lights and unplugged the clocks yet still it melts even the lowest rating fuse i put in. i have even had the fuse box open and closed the fuse contacts up after reading that fuses can generate heat if not making contact properly.
anyone got any ideas what to do next?

04-25-2015, 01:59 PM
What kind of fuses are you using? I hope they aren't from Harbor Freight

campermans cave
04-25-2015, 02:03 PM
any fuse i try melts within a few seconds of turning on the sidelights, i have gone through quite alot now fault finding and still come up with nothing, the fuse never blows just melts the plastic

04-25-2015, 02:03 PM
Daylight Running Lights. The headlights come on whenever you are running. But this doesn't turn on the dash lights, nor does it allow for high beams. Try turning on your lights to get dash lights.
Fuse #8 under the steering wheel? That would be the auxiliary fuse. Runs radio, heater fan and such. If it melts the fuse, I wonder what it is doing to wiring. I don't have a clue on this one. Current strong enough to heat the fuse should also blow the fuse. So I'm thinking heat from a nearby fuse?
One thing to check is the back lights. with age the bracket that holds the bulbs can get corroded and cause lots of issues. It can be cleaned.

04-25-2015, 02:49 PM
It could even be a problem with the fuse panel itself: melted plastic happens by heat.
A weak spring in the fuse holder would cause a high(er) resistance spot right there and that could melt the plastic without really stressing the fuse link itself.
(added: rereading your original posting shows you tested much of that...
question: if fuse 8 is not in place, can you feel any heat in that area of the fuse block? )

A full schematic of your Sprinter appears in chapter 8W of the service manual.
You can download the 2003 and 2006 manuals from http://aie-services-2.net/Sprinter/

As others have said, it could be a damaged wire anywhere along the way (cable cut as it goes around a sharp piece of metal).

good luck

Aqua Puttana
04-25-2015, 03:02 PM
Fuse #8... Terminal 30 opens a bunch of possibilities.

Fuse #10 is exterior lights and dash.

Melting plastic and not separating the fused link indicates a current essentially right at the rating of the fuse or a bad connection right at the fuse as Dick suggests. I wouldn't expect any one wire to overheat in that scenario. The wires should all be sized to the OEM fusing. High resistance shorts in a wire, that don't degrade over time, are pretty unusual. Damage to a wire or the harness would more likely create spot heating in that specific area that the fuse wouldn't even see, or that would cause it to blow immediately. Your wiring is not likely damaged, or being damaged by the consistent overload condition. I say that without ever seeing your vehicle.

Insert an ammeter with an in-line slightly larger fuse in place of the OEM fuse. Male slide connectors can be used to connect to the fuse clips.

Monitor the current while turning various things off and on. If that doesn't give a direction to a specific over-current then start disconnecting things like the radio harness and other items with plugs.

Did you say that you checked all the lamps for proper wattage? For one example, I know that the interior lamps come in a fairly large range of wattage in the exact same lamp type. Did someone tag on to the cigarette lighter circuit or Ter 30 for aftermarket?


campermans cave
04-25-2015, 04:51 PM
thanks for all the replies guys, i found that i was using cheap china fuses! now the fuse blows instantly. so now i know its a short of some kind. spent two days melting chinese fuses and giving myself a headache lol, now i can start again looking for a short

04-25-2015, 08:24 PM
lmfao. I win. You're welcome.

04-25-2015, 11:26 PM
since it blows when you turn on the lights, I'd say to check the back tail light assemblies. Easy to pop out and see, most likely to be the cause.

campermans cave
04-26-2015, 07:48 PM
thanks guys all done and sorted out, it was a wire grounding out behind the dash. a bugger to get to but an easy fix,
thank for all your input for a sprinter newbie very helpful bunch!


Aqua Puttana
04-27-2015, 01:30 PM
thanks guys all done and sorted out, it was a wire grounding out behind the dash. a bugger to get to but an easy fix,
thank for all your input for a sprinter newbie very helpful bunch!

Thanks for the follow-up. So much for my theory of it not being a wire problem. :bash: Did it appear to be a solid ground?

Was it actually Fuse #8, Fuse #10, or none of the above that was the problem?

One factor that may have contributed to the odd fuse behavior is the fuse quality issue Misterbond10 pointed out early on. Fuse technology is so old and basic as to vehicle circuits that to be honest I've never noticed fuses being very far out of range or a problem before. That can really throw a monkey wrench into things.

I have a Variac, diode bridge pack, some power resistors, and a DC ammeter in the basement. I also have an assortment of older and newer style vehicle type VW fuses, Bussman, etc. hanging around. I probably have some HF fuses too. Available time and interest being a factor, I plan to mess with things to see if I can duplicate the fuse melting issue.


04-28-2015, 12:22 AM
where does one find fuses (or anything else) that isn't made in China?

04-28-2015, 06:48 AM
i bought bussmann fuses an assortment on ebay, they are chinese, but the quality still is good, there are some made in mexico i think.

03-13-2017, 03:17 AM
I was at the junk yard the other day and pulled a pocket full of fuses from the cars and trucks. I think most were oem so I hope I am good for a while.
I like to keep a few on hand but with the different styles seems I am always out of the right size.

03-13-2017, 05:10 AM
ebay is great for fuses, people buy junkyard cars and tear all the OEM fuses out and sell them as a lot. check it out