V6 blowing 100A main fuse on Ignition OFF?

[Mrs Feynmans Bongos]

My Mazda Bongo camper van (1999, 70k miles, 2.5 V6 petrol auto) has developed a habit of blowing its main 100A "slow blow" PAL fuse.

This started to happen a year or two ago on Ignition OFF, since when I have been carrying spares, used two until ...
This week I had to turn out to rescue Mrs.B and show her how to swap 'em, but then a 2nd blew on Ign OFF at home! We are losing heart

Electrical history:

• We bought it "converted" from importer: all he did dc was add acc.socket for sink pump(+fitted ac hookup/sockets), no leisure battery
  But I have had to get the Alternator replaced twice:
• original 3 years ago (perhaps due to water ingress when rad blew "V6 Head Gasket, Coolant loss, Idling", "V6 SAGA.. blown radiator..")
• another last year (perhaps due to oil drips, given oil filler directly above , but 6 months after "V6 will not crank after flat battery")

My two ideas below, what do Bongo electrical experts think?

1. maybe main fuse blowing (not any sub-fuse) points to a cumulative effect ie no single faulty circuit? Eg is 100A now under-rated for (I hope) a mid-life vehicle, whose motors now draw more current than when new? Last year I measured 40-50A at battery leads (engine running with dead alternator). So it seemed quite plausible that, when about to turn OFF after a journey, fan running could add another 20-30A, whereupon closing say window/door ~20A could nudge it over the ton. I've bought 120A fuse to try, any Resettables out there?
2. but (1) sounds less likely than my 3rd Alternator on Ignition OFF spiking and blowing main fuse. Is this one failing too? On schematic "A-2 Starter & Alternator", there are paths via only "100A MAIN" (otherwise unfused) from both Alternator "2A" (RHS) and Starter Motor "A2-01" (LHS, but no probs at Ign ON!) Is there a diode pack that needs replacing? Or could some sort of inline TransZorb be retrofitted?

What else could I try, or have missed?
Help appreciated ...

[Mrs Feynmans Bongos]

Just seen recent thread "Fault code - help required"
Is the Diode pack alone retro-fittable, or is it built-into the Alternator?

I can find retrofittable blades, but not PALs and not enough current 6A Diode, 30A Resettable
But these look very interesting: 100A Car Automatic Circuit Breaker 12V DC Car Audio Inline Circuit Breaker
(Mrs.B would not have to wield spanner or socket near the battery )

[g8dhe]

I've only seen the inside of one Bongo alternator, thanks of Ady, but the various modules were all riveted in and hence not easily changeable without the proper tools and facilities (not surprising when it can handle 90 Amps), its best to get refurbed or replacement units.

[Mrs Feynmans Bongos]

Thanks Geoff.

I'm pleased to say that AutoJap have shipped me another recon V6 Alternator under warranty.
(Joe seems to be doing a fine job there, since he took over ... ) Fitting booked for 12 July.

I'm told some Alternators have a "clutch" that prevents them turning backwards on Ign OFF (which can give a damaging spike).
Does anyone know if Bongos use such an Alternator "clutch", especially V6?
If so, that failing might also be a candidate for origin of damaging spike >>100A (ie alternative to blown diodes therein, a short in the loom ...)

Before replacing Alternator, I will get garage to inspect relevant wiring loom for damage: is the routing given in "A2 - Starter & Alternator (J5-DE) 2nd page"?

Will also see if I can borrow a PCM code reader (in case the ECU, although primitive, knows sthg I don't )

[g8dhe]

I would suggest that heat is a more common cause for problems in this area, when the cam seals go oil flows down the length of the engine - via the alternator - before dripping onto the exhaust at the rear which is the usual warning smell that the seals are leaking. The oil flowing over the alternator causes it to overheat and eventually pop's the diodes.

[Mrs Feynmans Bongos]

Hmm... it's true my seals are somewhat middle-aged / leaky. But isn't it a huge job to replace them?

I wasn't brave enough to try eg Redex Oil StopLeak (someone told me it can cause other issues, inhibit future oil changes) Thoughts, ballpark price/recommendations for seal change?

I assume you noticed no clutch in those Alternator innards, Geoff?

So I think my best order of work is:
- Arrive at garage, fuse blows on Ign OFF
- Inspect Alternator sub-loom, is p21 correct for V6 routing?
- Remove failing Alternator, unless loom damage
- Change oil, mop-up all leaks, while no Alt in situ (in case of drips, given poor access under driver's seat)
- Replace Alternator +100A Fuse, MoT.....

[g8dhe]

There isn't a clutch in the alternator, its driven direct, you never need to disengage the alternator at all.
I used Forte seal conditioner for quite a while before the Cam belt needed changing to hold of the problem https://www.ebay.co.uk/sch/i.html?_from ... r&_sacat=0