Alternator Wiring to Amp Gauge.

[enigmas]

Hi guys,
I have an electrical conundrum. As I don't have a W.S Manual for a P5B saloon or coupe, I need a bit of clarification on how the Amp gauge on a Coupe is connected. Any colour coding would be helpful. To confuse matters, the car is a Saloon but fitted with a Coupe binnacle and gauges. I have no idea if a standard unmolested saloon has an amp gauge as part of the original factory instalation.

Any clarification on the wiring (coding) would be most helpful and appreciated.

* Yes, I do know how to wire up an Amp gauge but before I do any custom wiring conversion on Mike's car, I'd like to know about any existing wires that I need to chase down or locate first.

To confuse matters, the car is fitted with a non standard alternator.

[Mike’S-a-loon]

Hi Vince, the Saloon did originally have a ammeter in the cluster where the Tacho is now. It was a combined Ammeter/Fuel gauge/water temp.

[Phil Nottingham]

Both V8 Coupe and saloon have a shunted 60A scale ammeter, The connections are via a large Lucar busbar under the dash at the back over the parcel shelf. There are several large Brown and Brown and White cables on the busbar and a pair of lighter cables from the shunt to the ammeter

[enigmas]

Thanks Phil, so the BAT wire from the Alternator goes to the "busbar connector" first and then then to a terminal on the Amp gauge. The other terminal on the gauge goes to the heavy battery cable terminal on the starter solenoid...correct (?) like most cars of the period.

[enigmas]

Nov 11, 2021 6:52:46 GMT Mike’S-a-loon said:

Hi Vince, the Saloon did originally have a ammeter in the cluster where the Tacho is now. It was a combined Ammeter/Fuel gauge/water temp.

Do you recognize any of this Mike.



There's a small relay on the left, a fuse box with modern spade type fuses (1 dead red fuse) and a larger headlight relay.
It appears, without first pulling the alternator off for the moment, that a heavy gauge red wire from the BAT terminal on the alternator connects to that terminal spade fuse box. The cable loops under the front of the engine, from the DS to the PS.

There's also a small knob on a thermal switch in the grouping, which I'm guessing is to automatically set and turn on the electric fan in front of the radiator.

What is the small relay on the left for?
The car appears to have been fitted with an aircon at some time was it to switch on the aircon compressor.


PS.
Just realized, it could also be some thing simple.
Phil is there a fuse for the alternator circuit between it and the Amp gauge in the factory fitted fuse box on the firewall?

[Phil Nottingham]

None of that is standard P5B wiring in any way!

[Phil Nottingham]

Nov 11, 2021 8:24:25 GMT enigmas said:

Thanks Phil, so the BAT wire from the Alternator goes to the "busbar connector" first and then then to a terminal on the Amp gauge. The other terminal on the gauge goes to the heavy battery cable terminal on the starter solenoid...correct (?) like most cars of the period.

No - the ammeter wiring is (or should be) connected to a shunt (a resistance) - the shunt is connected to the busbar which has all the battery feed  connections

Attachments:

[enigmas]

Could you look at my last comment please Phil, where I've added a PS.

Ok, then apart from the shunt there's nothing unusual about how the Ammeter is wired up.
The shunt is probably there if the ammeter takes a dive.

[Mike’S-a-loon]

That setup was fitted by a mate of mine to take pressure off of the headlamp switch.

The thermostat should be for the electric radiator fan, as you suggest.

Yes, there was aircon fitted at some stage, but it was all defunct and the underbonnet bits were removed. The unit in the car was left in situ.

[Phil Nottingham]

Nov 11, 2021 8:56:55 GMT enigmas said:

Could you look at my last comment please Phil, where I've added a PS.

No fuses in the battery feeds apart from the single Purple Battery Control accessory fuse

[enigmas]

What does that fuse do Phil...if you remove it?

[enigmas]

Nov 11, 2021 8:57:07 GMT Mike’S-a-loon said:

That setup was fitted by a mate of mine to take pressure off of the headlamp switch.

The thermostat should be for the electric radiator fan, as you suggest.

Yes, there was aircon fitted at some stage, but it was all defunct and the underbonnet bits were removed. The unit in the car was left in situ.

He's seemingly taken the power feed straight from the BAT terminal on the Alternator. It should have been taken from the battery terminal on the starter motor!

I'll have to take a closer look tomorrow. I can easily bypass the ammeter and go straight to the battery terminal on the starter motor but I'll try and sort this first.

Interestingly Mike, with today's tech, simply fitting a modern set of LED headlight bulbs negates the need for headlight relays as the draw through the headlight switch is minimal. They also run cool. No need for the heavy current draw of halogen bulbs any more. Great lights hardly any current draw.

[Phil Nottingham]

Nov 11, 2021 9:06:07 GMT enigmas said:

What does that fuse do Phil...if you remove it?

The Battery Control fuse just protects the interior lights, horn,  cigar lighter(s) and clock. Not part of the charging circuit as such

[enigmas]

Thanks Phil. I'll just have to trace some of the wiring (factory original and owner added) to sort out what is occurring.
At least the alternator is still putting out a charging current...it's just not going to the battery?

On the plus side Mike (I'm sure you're reading this), the motor is starting and running very sweetly and all of your power steering system, reservoir and hoses included is off to Eddie's place to be fully refurbished and modified where required.

[Phil Nottingham]

To test the alternator to battery charge just connect to the main battery lead on the starter solenoid. How do you know its not charging? The busbar has all the connection

[enigmas]

When I check the alternator with a multimeter directly off the BAT terminal charging is indicated, but if I then check the battery in the boot directly it shows only the current status of battery voltage, no charge is occurring or being supplied to the battery.

Something (a wire/fuse/whatever) in the circuit between the alternator's output terminal and the battery is open circuit.
Tomorrow I'll connect a wire directly from the BAT terminal of the alternator to the positive battery terminal (easier than crawling about under the car) and I'm certain charge voltage will be indicated.

Also there's no indication of current reaching the ammeter. It will indicate towards the negative side if the headlights or other accessory is switched on, but no amount of revving the engine will move it towards the positive side.

There is a bit of wiring mayhem in place under the bonnet.

[Mike’S-a-loon]

Nov 11, 2021 9:54:39 GMT enigmas said:

Thanks Phil. I'll just have to trace some of the wiring (factory original and owner added) to sort out what is occurring.
At least the alternator is still putting out a charging current...it's just not going to the battery?

On the plus side Mike (I'm sure you're reading this), the motor is starting and running very sweetly and all of your power steering system, reservoir and hoses included is off to Eddie's place to be fully refurbished and modified where required.

Hey Vince,

Sorry about the charging, it was working post the alternator replacement and lighting mods, so I don't think it's systemic. Maybe the alternator has a fault? The original alternator caused a buzz in the regulator on the firewall, and the recommendation at the time was to replace it with an alternator with an integrated regulator, thus bypassing the old school regulator. It generally worked ok and kept the battery charged, though I did wonder if the boot mounted battery meant the resistance in the long cable meant it wasn't sensing the battery voltage accurately enough because occasionally in winter after a night drive with the wipers running it was noticeably sluggish on starting. That said, the ammeter would definitely swing into the "+" side, around 15 amps under revs, so I believe the setup was ok, if not perfect.

I spoke at length with Eddie earlier, he seems very confident he can repair the PS to the standard you said he would. He does reduce the pressure by about 20%, which I think will be advantageous in many ways. I think the original setup was a bit extreme in its level of assistance.

[enigmas]

One way or another we'll sort out the charging issue. The Amp gauge in the car was showing charge until it wasn't...and as I've stated, the alternator is still putting out charge but it's not reaching the battery.
The battery being housed in the boot is not an issue with either charging or starting as the main battery feed cable to the starter motor is about 1cm thick. The engine cranks over easily with its new 810 CCA battery.

The wiring attached to a couple of the alternator terminals is suspect from the point of view of safety. I haven't as yet looked at the wiring attached to the gauges, as the existing wiring I'm guessing would have had to be altered and lengthened to hook up to the coupe gauges lower down. We'll see what transpires.