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Isuzu instrument panel


Bro

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I'm not an electrician so need help.  Isuzu 35 engine with standard wiring and engine control panel.

Problem:-  Control panel warning buzzer is sounding, not continuous but with frequency increasing with engine revs, and engine alternator warning light is similarly showing.

On board electrical panel indicates engine alternator is pushing +14.4V and charging amperage is satisfactory (as is auxiliary alternator), both engine and auxiliary batteries charge fully no problem.

Both alternators bench checked OK so, looking at the Isuzu wiring diagrams I see 3 diodes at warning buzzer and thought I'd check them.  NO JOY!  Can't find diodes in panel wiring at all but do find 2 resisters (CGS SBCHE4   47R J PW LA) which according to the diagrams ought not be there.

Shall be grateful if someone will tell me what's going on as the sound from the warning buzzer is driving me crackers and I don't really want to disconnect it as it serves as warning for oil pressure and water temperature as well as engine and auxiliary electrics.

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Resistors usually sit across the back of the alternator warning lamps, they allow the alternator to function if the bulb fails - often left off the diagrams.

The diodes are usually in a plastic sleeve or piece of heat shrink tube. The mechanical fixing of the wiring to the diodes is a bit poor, and can break the diode leads. A quick trip to Maplins and a few minutes to solder some flexible leads to the diodes should fix it.

Steve (Eeyore)

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54 minutes ago, Eeyore said:

Resistors usually sit across the back of the alternator warning lamps, they allow the alternator to function if the bulb fails - often left off the diagrams.

The diodes are usually in a plastic sleeve or piece of heat shrink tube. The mechanical fixing of the wiring to the diodes is a bit poor, and can break the diode leads. A quick trip to Maplins and a few minutes to solder some flexible leads to the diodes should fix it.

Steve (Eeyore)

Thanks Steve for clarifying resisters issue (yes they are wired across the two warning lamps as you say). 

Not at the boat at present but took a photo of panel wiring before leaving last time and yes there does seem some plastic tubing on various cables so I suppose I must cut the tubing away to find diodes.

Having only a little electrical knowledge I assumed the diodes would be of reasonable size and clearly visible.  Can you suggest diode spec. I might ask for at Maplins?

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24 minutes ago, Bro said:

Having only a little electrical knowledge I assumed the diodes would be of reasonable size and clearly visible.  Can you suggest diode spec. I might ask for at Maplins?

Just take the broken one along, pick one that's a little bigger/robust. It's just a general purpose cheapie.

Edited by Eeyore
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12 minutes ago, Chewbacka said:

If they are just little general purpose diodes (less than an amp) then you want something like a 1N4003 - get them on ebay, 10 for a quid inc p&p

If you do go this route, note that 4001, 4003 or 4004 will be the same thing for your purposes. 

Ensure you solder them in the correct way around. 

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26 minutes ago, WotEver said:

What have I missed? How do we know that one of the diodes is faulty?

We don't.  Simply that both alternators seem OK yet the warning buzzer and engine alternator warning indicator light are active so I'm looking for possible cause.  Buzzer diodes seem worth a check.  Shall be grateful if you have other suggestions.

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Just now, Eeyore said:

Sorry its just a fault I have encountered - other faults are available B)

One or more of them may well be faulty but a multimeter check can prove that in seconds. Pulling the sender wires off the other things that make the buzzer, er, buzz is even quicker. 

  • Greenie 1
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27 minutes ago, WotEver said:

I already gave one in post 2. 

 

Would "Oil Pressure sender" or "Temp sender" circuits cause the alternator warning light to activate?  I'm no electrician.

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9 minutes ago, Bro said:

Would "Oil Pressure sender" or "Temp sender" circuits cause the alternator warning light to activate?  I'm no electrician.

They'd make the buzzer sound and with the back EMF from a buzzer across the warning lights, who knows? The fact is that it's a simple test that will take seconds and if it's not either of those senders then you'll have wasted a minute or two of your life proving it. 

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57 minutes ago, WotEver said:

They'd make the buzzer sound and with the back EMF from a buzzer across the warning lights, who knows? The fact is that it's a simple test that will take seconds and if it's not either of those senders then you'll have wasted a minute or two of your life proving it. 

Many thanks.  I'll do just that as soon as I get back to the boat (week or so).

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16 hours ago, Bro said:

I'm not an electrician so need help.  Isuzu 35 engine with standard wiring and engine control panel.

Problem:-  Control panel warning buzzer is sounding, not continuous but with frequency increasing with engine revs, and engine alternator warning light is similarly showing.

On board electrical panel indicates engine alternator is pushing +14.4V and charging amperage is satisfactory (as is auxiliary alternator), both engine and auxiliary batteries charge fully no problem.

Both alternators bench checked OK so, looking at the Isuzu wiring diagrams I see 3 diodes at warning buzzer and thought I'd check them.  NO JOY!  Can't find diodes in panel wiring at all but do find 2 resisters (CGS SBCHE4   47R J PW LA) which according to the diagrams ought not be there.

Shall be grateful if someone will tell me what's going on as the sound from the warning buzzer is driving me crackers and I don't really want to disconnect it as it serves as warning for oil pressure and water temperature as well as engine and auxiliary electrics.

These problems are often associated with the multi connector in the harness between engine and the instrument panel. Before doing anything else I would pull it apart and clean it up with switch cleaner. A common problem on a lot of modern engines that use a similar connector.

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