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Hi Folks, I'm on the final stage of a nut and bolt resto, having converted LHD to RHD . Today I fitted a new wiring harness supplied by Moss. Fitted with no real issues but I had to change the ignition switch from the old prong style to a new Lucas with a connecting plug. When I started the engine very quickly the charging cable from the alternator started to smoke, I immediately stopped the engine. The alternator had been away for overhaul. When checking all connection's I noticed the connecting block for the ignition to wiring harness the wires appear to connect incorrectly, as if either Moss ( supplied I believe by Auto Sparks) or the bran new Lucas switch has been incorrectly installed. See photo. Could this be the issue? I have a volt hand held meter which I could attach to the alternator but what should it read? The larger brown cable from the alternator is the one that started to melt, just got to it in time. Thanks in advance. Paul Richard Drescher

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As you say, the wiring to the switch doesn't look right Paul.  Logically, brown should go to brown and white to white but depending on the switch innards, it might still work connected like that. 

However, I don't think that is anything to do with the alternator wire overheating. There must be a short to earth somewhere to do that, but that thick brown wire should go direct to battery live.  Obviously it doesn't else the battery would have shorted out too.   Did the overheating only start after you started the engine? 

What type of alternator is it?  Is there only one thick output lead?

 

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Hi Rob

Thanks for the reply. I bought a brand new postive battery cable from Rimmers, it has the in line conector for the 3 brown (N) wires so its just plug in the wires from the harnes into tye connector, but as you suggest it feels like there is a short when the engine is "running" nothing happens when the engine is not operating and the battery cables connected. Deffinately struggling with this issue and really dont want to ruin the new harness.  What I have noticed when doing the rebuild the original brown charging cable from the alternator had been chopped off and repalecd with a heavier duty cable why ?? Lucas Alternator but I cant find any ID for the model/serial number etc. 3 Cables, one large and two small, large brown is the one that overheated as soon as the engine started to "run"

Regards Paul

 

 

 

 

Paul

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Two small cables on the alternator is odd.   There should be a thin brown/yellow which is the ignition light feed and the other two should both be heavier cables to the battery connection so it is even more odd that it is only the larger of those which is getting hot.   

Since the overheating only happens with the engine running it must be the output from the alternator doing that, either going to earth or into the battery. There can't be a short in the battery lead as that would be catastrophic and permanent. That makes me think there either is no connection from the alternator to the battery or perhaps the output from the alternator is very high so it is trying to pass a high current into the battery.  

For a start you could disconnect the alternator and measure the output voltage. It should be around 14.7 volts. 

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15 hours ago, Paul Drescher said:

Hi Rob

Thanks for the reply. I bought a brand new postive battery cable from Rimmers, it has the in line conector for the 3 brown (N) wires so its just plug in the wires from the harnes into tye connector, but as you suggest it feels like there is a short when the engine is "running" nothing happens when the engine is not operating and the battery cables connected. Deffinately struggling with this issue and really dont want to ruin the new harness.  What I have noticed when doing the rebuild the original brown charging cable from the alternator had been chopped off and repalecd with a heavier duty cable why ?? Lucas Alternator but I cant find any ID for the model/serial number etc. 3 Cables, one large and two small, large brown is the one that overheated as soon as the engine started to "run"

Regards Paul

Hi Paul,

Have you wired the Starter correctly? As there is a big brown wire going to it from the Alternator via the socket on the power feed positive red wire. Is that the one that is shorting out?

Bruce.

 

 

 

 

 

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Bit of a sideways step.  Here is an original 1972 Butlers switch from another Triumph. (Date stamped 9. 72.)
Colour connections may guide you or confirm your suspicion.   The Autosparks loom from Moss I commissioned the remaking of from a genuine unused loom many moons ago.

  It does look like your green box Lucas switch is odd.

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Edited by BlueTR3A-5EKT
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Hi Latest update-

1.Removed the alternator connector, remove the 3 wires from the plastic connecting block, removed the brown/yellow wire that goes to the alternator warning lamp, I check continuity and no issues, not going to earth but straight from the alternator to the lamp holder good circuit

2. Removed the small brown cable from the Alt connector, disconnected it from the battery positive cable connecting block, again not earthing and good circuit

3. Removed the large brown charging cable from Alt to battery positive connection block, no issues again.

4.Started the engine and Alt output was good about 13 volts on tick over.

5. Started the engine and reconnected one wire at a time. no issues on all three, no hot cables ??? so I have no idea why different this time, but I did fasten the + and - battery cables tight this time and not left loose as it was when the charging cable overheated. The volt meter in the car works showing 12v but the alternator warning light goes out when the engine is running but when I switched the ignition to off and remove the keys the light comes on as if it’s getting a "feed" from the alternator so I’m very confused now.

Regards Paul

 

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12 minutes ago, Paul Drescher said:

but when I switched the ignition to off and remove the keys the light comes on as if it’s getting a "feed" from the alternator

Unfortunately that means that one of the main diodes in the alternator has gone short-circuit, allowing current from the battery to flow back through the control circuit.   When the alternator isn't running the diodes should block any reverse current flow. 

 

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Its fairly easy (and much cheaper) to swap out the diode stack Paul  -  though it does involve some soldering. 

 

 

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