big blue fuse blown...

[bongomaan]

hi everybody,long time no need to post in this section but i do observe, a couple of months ago i had the alternator reconed and two days later the big 100 amp fuse next to the battery blew,took it back and the man checked it all out and said all was ok and it was till Saturday when mrs bongomaan phoned me in work to say the vans gone mad and all the alarms went off,wipers, lights everything then it stopped,when i got there the 100 amp fuse had melted,so i replaced it and then it has gone again today..at the moment mrs b is 7.5 months pregnant and unable to get into our other motor (kia pride) so i need to get it fixed asap,for some reason i suspect the aircon and have removed the 10 amp fuse as it seems only to go when it is on.nothing has been done to the van for ages as its been going like a dream...all ideas appreciated...regards neil...also i think an auto electrician would be a waste of time....

[Doone]

There is a similar problem where 'Lloydy' mentions that a 3 month old faulty alternator had blown the 100amp fuse and caused an alarm to sound - it may help - HERE.

[g8dhe]

I don't have the circuit diagrams with me (still mobile in the Mendips) but there isn't much that can take out the 100 Amp fuse on its own, other than the alternator or a very major (and it would be very obvious) fault in the wiring loom. I'm downloading the diagrams from home at the moment and will check, but I would suggest an intermittent cable fault leading to the alternator or within it.

Yup just checked diagram here;
Click for fullscale image
If the 60 Amp fuse is OK then it can only be a problem with the alternator, either it is earthing the main cable intermittently, or for some reason the battery side of the fuse is drawing 100+ Amps that is coming from the alternator (very unlikely) I would show your alternator man the diagram and suggest that he might like to inspect the alternator much more closely!!!

[bongomaan]

hi guys,nice bit of info there...i think the best thing to do now is check the battery to alt lead and if ok back to the alt man with me,will keep you posted...are you a sparks geoff you are always on the case....cheers neil....

[bongomaan]

right, then went to see alternator blokey on friday,he had it out on the bench for some time and pronounced it healthy,but did say that if there was anyway he could help he would....soo for a week and a bit it has been ok running without the aircon fuse in,so Saturday i replaced it and true to form this morning as mrs b-man was talking no"1 child to school,5 yards down the road,both coolant alarms going off,wipers going off on their own,lights flashing then nothing, causing me to have to come out of work and mrs b-man to have to go to see mrs farmer at the school because of second late arrival of no"1 child,please help us because if poppy is late again my missus will have to go and see mr mac.....and nobody wants to see that.i have checked the cable from alt to battery and all seems well something in me bones tells me its something to do with air con........cheers....

[g8dhe]

The Air Conditioner Fuse is a 10A down on the internal fuse panel by the drivers knee, so I don't think what your reffering to can be the Air Con fuse ? Can you tell us where the fuse is that you have had out for the last week, what it is rated at and which of the three fuse boxes its located in. Also I assume that when the 100Amp fuse goes you are replacing it with the same type of fuse ?

[g8dhe]

I see looking back at your first post you are reffering to the 10Amp fuse down by the drivers knee for the Air Con. The trouble is all the other circuits that run from the 100Amp fuse have there own lower rated fuses in the boxes under the bonnet. I would suggest that you check all the fuses under the bonnet to make sure that they are first OK and second that they are the correct rating ! I'm wondering if another fuse has been replaced with a higher rated one and hence a fault on some other circuit (possibly the Air Con) is blowing the main fuse rather than its own one.
There is a factsheet on the club site which lists the fuses and the ratings do note that the positions of the fuses changed for vehicles after September 2001, I wonder if possibly the fuses have been put in the wrong positions in which case you would have the 100Amp in the Engine Management position instead of a 30 Amp, and a 30 Amp fuse in the main battery position which might explain the problem ?

[bongomaan]

hi geoff,i had a look and all seems as per fact sheet i checked all the fuses,it is strange that no other fuses have blown..the only logical answer is the lead from the alternator to the battery i wonder if i could try a bypass cable to try test this thought ? what cable would i need ? mrs b has informed me that the air con/heaters were not on monday so maybe not that,but there is a lead between the alternator and air con pump...

[g8dhe]

Any short to the chassis from the cable running from alternator to the fuses is going to be pretty obvious, its going to be able to carry well over 100Amps to blow the fuse so its not going to be a minor abrasion, check the length of the cable especially where it runs near the chassis at any point.

There shouldn't be any connections to the air. Con., or its fans, going directly to the alternator - if there are then somebody has been adding things incorrectly and all bets are off !

I notice from your other posts, that the problem has been going on for some time, starting with problems with the leisure battery back in June when it was blowing the main fuse. Have you checked all the L/B cabling ? Is the connection to the L/B charging relay correctly fused at both batteries. Do you know who fitted the L/B and its wiring or have any details of it ?

[bongomaan]

hi geoff,there is a plug with a small loom coming out of the alternator and there is a single thin wire that goes to the air con pump,i have disconnected this though.i dont have a lesure battery so maybe i was commenting on someone else s post,i am going tomorrow to get a second opinion on the alternator,i spoke today with a mechanical mate and he advised me to double check it....thank you for your help geoff its keeping me going at the mo...with all that life chucks at you its the last thing i need is an unreliable vehicle.....cheers...

[g8dhe]

OK, I think you will find that the extra wire your referring to is coming out of the wiring loom but doesn't have anything to do with the Alternator as such, it appears to operate a solenoid associated with the Air. Con which is located near to the alternator (going by the location diagram not always the most accurate of diagrams) and only seems to be used on the electronic version of the Air. Con. not the manual ones. There are two thinner wires which go to the alternator, one provides a 12 volt source for the field windings (to generate the magnetic field), and the other signals back to the Charge lamp on the dashboard to indicate when the alternator is not producing any current.

A thought occurs to me have you had any work carried out on the glow-plugs, in the past others have had the Glow plug bus wire shorting to chassis, this would normally blow the the fusible link that connects directly to the battery, but if your battery was at all low then with the alternator generating current it could be drawing sufficient current thru the 100Amp fuse, along with the battery charging current to cause the 100Amp to go. For this to happen the glow-plug relay would also have to be operated, normally you can hear this clicking, but I'm not sure if you would once the engine was running (You would if it was a V6 but there again a V6 doesn't have glow-plugs . Anyway it might be worth checking that the glow-plug bus wire/rod isn't touching the head anywhere or very close to it and just making contact on occasions.

Incidentally has this happened when you've been driving it or only when your wife has been out in it ? (I'm not casting aspersions (I've never passed a test myself!) just wondering if you would have noticed anything else happening just prior to the fuse going).

[bongomaan]

hi g8hde,i have checked the glow plug rail and all is well,i got another opinion on the alternator and it to is ok however while he had his multimeter on the battery i switched the aircon on and the volts dropped from 14 down to 12 this is not right according to him but it still works???? so do i need a new a/c pump or is usual to get that voltage drop....maybe some kindhearted bongoler could try the same thing on their battery and post their results.....cheers neil...

[g8dhe]

If the engine wasn't running then a drop from 14 to 12 would be expected, although I would be surprised that you were already at 14 volts to start with. If it was running then yes that is surprising ? What sort of Air. Con. do you have a manual one or the electronic version with a display ? If it is the Air. Con. causing the problem then I will be very surprised unless one of the fuses is incorrectly rated !

[bongomaan]

yes the engine was running,sorry if my posting isnt clear but i have a lot going on...i have the digital aircon/climate control and i have checked the fuses but will go through them again,i can see that the fuse(100 amp) i put in on friday is slowly melting......oooh i think although im on expectant daddy rushing to the hospital type duties i think a small tot of rum is in order to bolster moral....cheers .....

[g8dhe]

It sounds like several circuits are drawing close to there individual maximum's, not enough to blow the individual fuses, but sufficient to add up to the point where it is blowing the 100Amp main fuse. I think it might be time to get a local auto electrician to take a look at the current being drawn by each circuit,otherwise the vehicle is going to fail when you need it most.