Defender v8 - Battery Charging Failure when warm

[mikejones66]

Hi Newbie

Have bought a very good 80% complete project a great new build but with a known problem, need some electrical expertise.

Defender diesel now with a 3.9 Rover EFi V8 -

1. Car was a diesel Landrover defender and has a TD5 wiring loom in place for lights, dash, tow pack etc

First note - no dash lights when you turn ignition on - no oil, power, indicators light, main beam etc ? )

From cold car is perfect starts easy and moves off well after 20 mins you start to notice speedo fails - then fuel gauge fails and radio power loss the car comes to a stop - battery flat

2. The v8 has its own ECU serving the V8 wiring loom ( only link I can see between the two looms is the temp sensor and fuel guage - a brand new alternator shows its charging the battery when running from a cold start with a meter across it - but when running for a short while the alternator stops charging the battery followed by engine shut down and fall battery.

Jump pack on the car and it starts straight away and runs well -

Ideas and solutions welcome as I suspect this is not the first time this engine transfer has been done -

many thanks for your anticipated advise for a newbie

[ChrisJC]

So the charging circuit is completely unconnected with the EFi system as far as I know.

The alternator 'large' terminal is just connected to battery positive, and the 'small' terminal is connected via the charge light on the dash to the ignition switch.

Are you able to confirm that is how it is wired?

Chris.

[mikejones66]

Many thanks for your reply - I have no dash lights - so maybe that's it ?

I can test out the wiring alternator to dash and come back to you tomorrow -

But if that is the case why would the alternator charge when the motor is cold and then stop after 15 mins when the engine warms up ?

Appreciate you taking the time to reply

[ChrisJC]

Many thanks for your reply - I have no dash lights - so maybe that's it ?

I can test out the wiring alternator to dash and come back to you tomorrow -

But if that is the case why would the alternator charge when the motor is cold and then stop after 15 mins when the engine warms up ?

Appreciate you taking the time to reply

In theory, if the 'small' terminal isn't connected, the alternator might still charge. But I wouldn't rely on it.

It is 100% worth you getting the dash charge light to work as expected, then all will probably be OK.

Chris.

[mikejones66]

Ok thanks that's the priority then

Appreciate it Chris

[DEVONMAN]

I would check out the battery terminals and the battery itself and the earth from the battery to the engine block / chassis.

Good luck,
Denis

[DaveEFI]

On most alternators, the ignition warning light circuit is part of the charge circuit. If the bulb blows, it won't charge. Since yours appears not to be connected or whatever, that's probably the reason.

When you say it was checked and was showing a charge with a meter, what was the reading?

[ChrisJC]

On most alternators, the ignition warning light circuit is part of the charge circuit. If the bulb blows, it won't charge. Since yours appears not to be connected or whatever, that's probably the reason.

When you say it was checked and was showing a charge with a meter, what was the reading?

On all the instrument clusters I have looked at, there is a resistor in parallel with the charge light. I presume the idea is that if the bulb blows, you still have a functioning charging system.

Chris.

[DaveEFI]

Yes - a parallel resistor is used on some. But it's not universal - my SD1 doesn't have one. So you'd need to check the schematic for the particular vehicle.

But if none of the warning lights are working, sounds like something is unplugged or whatever. And likely the resistor, if fitted.