Electrical fire in engine bay

[evanmc]

1985 2.5 NA 110

As much as I enjoy making repairs, this is getting to be a bit much.

A week ago, I reconnected the battery after some repairs and heard a small pop, and smoke rising from inside the alternator. Fortunately there is a shop here that specializes in alternators and starters, so I had it repaired.

Today I installed the reconditioned alternator, reconnected the battery (I have a knife switch, so no fumbling here). No pop, but within moments, the wiring harness was ablaze. Fortunately, a fire extinguisher was nearby, so n damage other than my ruined wires.

The wires that melted and burst into flame appear to be the two that connect to the alternator and snake back around the engine to the back of the starter solenoid.  Does that connection sound right? I am not adept at all in reading wiring diagrams.  There are three wires on the alternator -- two brown outputs, and one thinner brown/yellow.  It was the two brown wires that melted. Other wires in the harness where just collateral damage.

OK, some clarifications and then some questions:

I have used this alternator for years with no problems, and I have not changed the wiring or added additional electrical load to the system.  Prior to this I started and ran for a bit just fine with the alternator disconnected.

Any idea what could have caused this?  I just don't want to get a new wiring harness in only to fry that as well.

Can I try this out first by connecting the alternator to the starter solenoid?

And here's the bit I did not reveal -- years ago I replaced the original alternator with a higher output one, but did not change the wiring harness -- I see now that the parts catalog has options for higher amperage. Once again, this was years ago, should I use a different harness when I reinstall?  The engine ID is 12J31922C, so the parts fiche tells me to use PRC4785

 

Thanks,

-Evan-

[monkie]

It sound to me like you have inadvertently earthed a live wire somewhere. I did this once with the glowplugs resulting in me having to replace wire from the alternator to the ignition switch. It only takes the slightest touch of a live connection to the engine block or other earth point so it can be easily overlooked.

[miketomcat]

That or the pop last time melted the wire insulation enough that when you refitted the alternator. The wire rubbed though/already had and shorted to the block thus causing the rest to melt and catch fire.

Mike

[evanmc]

Thanks. So can I try connecting the alternator directly to the starter connection before I try this with a new harness?  Don't want to end up crying a new harness if the problem is elsewhere.

[steve b]

I'd be using a meter to check the main current out terminal on the alt. for a connection to earth before reconnecting any power . If all good then a test connection to the starter can be done . The engine loom section does suffer over time from heat hardened insulation so renewing it is good , they also chafe around the back of the block if not well protected and secured .

cheers

Steve b

[western]

16 hours ago, evanmc said:

1985 2.5 NA 110

As much as I enjoy making repairs, this is getting to be a bit much.

A week ago, I reconnected the battery after some repairs and heard a small pop, and smoke rising from inside the alternator. Fortunately there is a shop here that specializes in alternators and starters, so I had it repaired.

Today I installed the reconditioned alternator, reconnected the battery (I have a knife switch, so no fumbling here). No pop, but within moments, the wiring harness was ablaze. Fortunately, a fire extinguisher was nearby, so n damage other than my ruined wires.

The wires that melted and burst into flame appear to be the two that connect to the alternator and snake back around the engine to the back of the starter solenoid.  Does that connection sound right? I am not adept at all in reading wiring diagrams.  There are three wires on the alternator -- two brown outputs, and one thinner brown/yellow.  It was the two brown wires that melted. Other wires in the harness where just collateral damage.

OK, some clarifications and then some questions:

I have used this alternator for years with no problems, and I have not changed the wiring or added additional electrical load to the system.  Prior to this I started and ran for a bit just fine with the alternator disconnected.

Any idea what could have caused this?  I just don't want to get a new wiring harness in only to fry that as well.

Can I try this out first by connecting the alternator to the starter solenoid?

And here's the bit I did not reveal -- years ago I replaced the original alternator with a higher output one, but did not change the wiring harness -- I see now that the parts catalog has options for higher amperage. Once again, this was years ago, should I use a different harness when I reinstall?  The engine ID is 12J31922C, so the parts fiche tells me to use PRC4785

 

Thanks,

-Evan-

           PRC4785 is Engine Harness 45amp  alternator on 90/110 from Engine No: 11H05639C to November 1989

there is another loom for 65amp alternator engine looms,  from Autosparks 

 

LAND ROVER DEFENDER 90 & 110 ENGINE WIRING HARNESS

PART NO:LR423YEAR:upto Nov 1989FINISH:PVC Cables with a Taped Outer CoveringCHASSIS NO:upto 404682

Defender 90/110 Engine Harness with Optional 65 Amp Alternator. PRC4021

[Eightpot]

The two brown wires take the charge output directly to the battery, via the main battery terminal on the starter motor. 

I would guess that one of the terminals on the end of the brown wires is touching the alternator case, the engine or the case of the starter motor - which basically earths  it out and turns the brown wire into an electric fire. 

[evanmc]

OK, a direct link from the alternator to the starter solenoid produced no smoke.  Must have been age/wear in the wiring harness.

Next question, is the major difference in the 65 AMP harness (PRC4021) and the 45 (PRC4785) The gauge of the alternator wire?

Or does the 65 AMP use a single large gauge wire instead of two smaller wires?  I can't seem to find a picture.

BTW: lesson learned about fire extinguishers. that dry power made a huge mess. Just ordered a halon one.

-Evan-

[monkie]

Full marks for having a fire extinguisher though and save your Land Rover. I wonder how many of us don't have one.....

[western]

6 hours ago, evanmc said:

OK, a direct link from the alternator to the starter solenoid produced no smoke.  Must have been age/wear in the wiring harness.

Next question, is the major difference in the 65 AMP harness (PRC4021) and the 45 (PRC4785) The gauge of the alternator wire?

Or does the 65 AMP use a single large gauge wire instead of two smaller wires?  I can't seem to find a picture.

BTW: lesson learned about fire extinguishers. that dry power made a huge mess. Just ordered a halon one.

-Evan-

the 65amp loom still has 2 wires from alternator, recently replaced mine, add a big thick cable from alternator to starter solenoid connections to handle the current increase

[neil110]

11 hours ago, evanmc said:

OK, a direct link from the alternator to the starter solenoid produced no smoke.  Must have been age/wear in the wiring harness.

Next question, is the major difference in the 65 AMP harness (PRC4021) and the 45 (PRC4785) The gauge of the alternator wire?

Or does the 65 AMP use a single large gauge wire instead of two smaller wires?  I can't seem to find a picture.

BTW: lesson learned about fire extinguishers. that dry power made a huge mess. Just ordered a halon one.

-Evan-

At least with a dry powder extinguisher you don't run the risk of asphyxiation if it is discharged in a relatively confined area. Have you considered foam?

[western]

you can't buy new HALON extinguishers in UK/Europe any more, they were banned as ozone depleting source. https://www.fireandsafetycentre.co.uk/advice-centre/halon-fire-extinguishers/

but it may be possible in USA where you are.

 

[monkie]

I think Halon is also banned in USA, but there are alternatives of a similar principle that aren't ozone depleting.

[evanmc]

Yes, I was using "Halon" in the kleenex sense, as a generic.  I believe the alternative is "Halotron".   I suppose I could have gotten a CO2 model.  I am now prepared for my next fire (which will hopefully never come)

https://www.amazon.com/gp/product/B00F5CK8VY/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1

Thanks for the advice on this -- I ordered a harness from Autosparks.  I usually get genuine parts, but this seems like fine quality for a lower cost.

-Evan-