Hot electrical junction near steering column - normal?

[Aerial_stu]

Hello, whilst trying yoga this afternoon, looking for loose bits to tighten to suppress some of the rattles I discovered this two pronged device with a green bridge that was getting very hot when the ignition was on.  (I had the ignition on to test my heated window connection).

Is it meant to get so hot so quickly?  Whats it for please|?

Thanks, and sorry the photo is upside down!

Stuart (Sigma 2016 SV)

 

[Jonathan Kay]

It’s a resistor. And they get hot in normal operation. 

Jonathan

[Aerial_stu]

Simple, thank you (again) Jonathan.

[rj]

It could be a ballast resistor for the alternator warning lamp - in which case it should only get hot when the engine is not running.

What colours are the wires it connects to?

[Aerial_stu]

Hi RJ, the engine was off at the time so makes sense.  The coloured wires are just visible in the photo.

[rj]

Hi Stuart

Tracers etc on the wires may be hidden. Hence my question. I'm unsure if it's a brown with a yellow tracer and a green with grey tracer. But yes, it makes sense - especially if the warning lamp is an LED.

[Jonathan Kay]

Jonathan

[rj]

Could you also turn the wires, please? Then I can better see colours and tracers.

[aerobod - near CYYC]

Definitely looks like the 68 Ohm excitation resistor between the alternator warning light and alternator. The wires for that are brown/yellow and green. It is rated at 4W, so is designed to take the current and get quite warm.

[John Vine]

What James says (#9).

I sent CC the same question 3-4 years ago, along with this photo:

 

They replied:

"The resistor in the picture is to prevent the alternator light on the tacho from coming on and yes it will get hot."

And from the Assembly Guide:

 

It gets hot when the ignition is switched on, but cools down again once the engine starts.

JV

[ChrisC]

Isn't it speed sensor related, gets hot if the sensor stops in an on position (could be hot when off). Green and Yellow Black are also speed sensor colours. I believe it's used to convert the speedo to use a NPN or PNP sensor. 

[aerobod - near CYYC]

That is a separate 1K ohm resistor that is in the speedo feed, Chris, the 68 ohm one is in the tacho warning light feed.

[revilla]

That's interesting ... I've seen a few K Series now where the alternator does not start reliably and I've found the current supplied by the LED warning light (about 4mA) just isn't enough for an alternator that was designed to have incandescent lamp as a warning. The K Series cars don't have a parallel resistor like that (and really should have). A 68R resistor will be pretty close to a 2W lamp and makes sense.

[Jonathan Kay]

See also:

https://www.lotus7.club/forum/techtalk/2005-k-series-alternator#comment-2373318

 

https://www.lotus7.club/forum/techtalk/wosp-alternator-fitting

 

But is this only a problem when the same circuit is used for energising the alternator and for the warning lamp?

 

And is:

 

"The resistor in the picture is to prevent the alternator light on the tacho from coming on and yes it will get hot."

 

different from it being there to allow enough current in the energising circuit?

 

Thanks

 

Jonathan

[revilla]

Hi Jonathan,

I'm not sure about all of the different alternators that people fit in place of the standard Rover ones and those fitted to models other than the K Series but:

The failure to start charging will be caused by insufficient excitation current. That's only going to be caused by the fact that an LED has been used as the warning lamp if the two circuits are one and the same.

An LED indicator will actually glow visibly at a very low forward current, so if the alternator continues to draw even a milliamp or so on the excitation wire after it starts, an LED indicator could still appear to be lit. However an LED requires a forward voltage of typically about 2.2V before it starts to pass current. If you put a 68 Ohm resistor in parallel, you would need to be drawing 32mA to produce 2.2V across it before the LED even started to light. 

So you can read the "to prevent the alternator light on the tacho from coming on" in one of two ways:

1) It may prevent a failure to start charging, which means it stops the LED from genuinely coming on (to indicate a failure to charge).

2) It may prevent the LED from spuriously coming on (when the alternator is charging but there's still a small current draw on the excitation wire).

As far as I know, the main vehicle loom for EU2 (certainly later EU2 models) and EU3 is basically the same. I've often wondered why this issue of the LED indicator leading to a failure to excite the alternator seems to be something of a recent phenomenon - I can't find many references to anything similar from the time when these cars would have been newer. On my car, the LED only feeds about 4mA into the excitation wire, but it seems to get away with it. I've only really had a chance to look at this on my own car and others which have been experiencing the problem, but I did wonder if on the K-Series era cars there may have been a resistor like this built into the tacho where it cannot be seen; and as they do run hot, I wondered if they were actually burning out eventually, leaving just the LED current and marginal startup performance.

If you fancy getting your multimeter out and checking what excitation current your warning light is feeding, I'd be interested to know!

Andrew

[Jonathan Kay]

Thankyou very much.

"I've often wondered why this issue of the LED indicator leading to a failure to excite the alternator seems to be something of a recent phenomenon - I can't find many references to anything similar from the time when these cars would have been newer. On my car, the LED only feeds about 4mA into the excitation wire, but it seems to get away with it. I've only really had a chance to look at this on my own car and others which have been experiencing the problem, but I did wonder if on the K-Series era cars there may have been a resistor like this built into the tacho where it cannot be seen; and as they do run hot, I wondered if they were actually burning out eventually, leaving just the LED current and marginal startup performance."

Isn't it interesting? Even if we narrow down the Sevens at risk to those with LED warning lights AND combined circuits for the warning light and excitation there might be something else, but I suspect that it's variation between alternators.

These observations are going to make it much quicker to pinpoint problems.

Jonathan