410 Wiring

[DODD]

Hello,

Can anyone help me identify some of the wiring behind the dashboard of my 410.
I have had the entire dashboard out and completed the works as I intended. During the works I found quite few redundant wires, most of which I was able to trace and remove or isolate properly; however, I found a small bunch of wires taped together and I am unable to locate their source or their intended purpose: this bunch comprises of:-
1No. 5.5mm Brown cable
1No. 5.5mm Brown & White cable
1No. 3.5mm Brown/Red trace plus 1No. 3.5mm Brown cable (joined together)
2No. Brown & White cables, one at 3.5mm and one at 4mm (joined together)

All the above cable diameters are measured across the outside of the insulation, I see little point at this time cutting the sheathing back to measure the core diameter.
All of these cables are terminated with electrical eyelet connectors.
None of the cables appear to carry any current whether the ignition is on or off.

I don’t think they are from the select-a-ride system which had been removed prior to my ownership but they may be part of a air conditioning system which was installed at some point and subsequently removed, again prior to my ownership.

While working on the electrics I intend to introduce an electric isolation switch to the fuel fuel pump near the dashboard. The wiring diagram I have doesn’t show the fuel pump or the associated wiring, only the wiring to the petrol reserve valve. The wire at the pump is a white cable; am I correct in thinking that one of the two white wires on ignition switch actually goes direct to the pump or is it part of another circuit?

Any help will be very appreciated.

Regards

Brian

[David C]

From 410 wiring diagram 410-1-68036

Brown wires are permanent live prior to fuse.
To fuse box
To ammeter
To heated rear window in line fuse

Brown/red goes from ammeter to ignition switch

Brown/white from alternator to ammeter then ignition switch and lighting switch

Strangely, the fuel pump is not shown but all feeds from the switched live fuse are purple

A white wire from the ignition switch goes into a bullet connector and splits to the ballast resistor via a loop round the tacho on one leg and to switched live fuse on the other

The other white wire from the ignition switch feeds the petrol reserve switch and heated rear window switch via a connection on the tacho

[David C]

This wiring diagram also omits the wiring for the Armstrong shock absorbers.

[Kevin H]

I didn't know the 410 had an electric fuel pump?

[David C]

They do, or at least did from new. Double ended SU. From memory it's AUF404 as fitted to Rolls Royce etc.
A good few will have been replaced with high output rally / race pumps but these are usually quite noisy. The usual point of failure on the original was mechanical points. A very good upgrade for these was readily available from the nineties. Although the double ended pumps were quite rare they shared components with single ended pumps used on huge numbers of BL cars.

[GeorgeG]

Re the isolation switch for the electric fuel pump, I decided to fit one in my 408 Mark 2 and pondered for a while on the best position for the switch. In the end I decided to use the Selectaride switch (which has been redundant in my car since I acquired it).

The pump current is too high for the switch to take, so the switch works a relay. The system works fine in the garage but I'm 2-3 weeks away from the first road test for the car in 25 years! I think the switch is likely to be the least of the inevitable teething problems.

George

[Roger Morrall]

Originally Posted by DODD

Hello,

Can anyone help me identify some of the wiring behind the dashboard of my 410.

Brian

You may find it helpful to refer to the 410 wiring diagrams that I posted 26-11-2019 under the thread 410 Alternator charging fault. (At that time my nom de plume on this forum was PEU186F).

The comment that I made at that time re starting with a large sheet of clean paper and drawing out the alternator - ammeter - battery connections for yourself still stands as it is almost impossible to gets ones head around those parts of the circuit from the original wiring diagram. In essence any wire that is brown or brown with a tracer is or should be part of that core alternator, battery, ammeter circuitry.

So thick brown wires that don’t apparently go anywhere really are a big anomaly

I surmise that somebody may have disconnected and bypassed the ammeter (which had happened on PEU186F) which is something that can be achieved by rearranging the connections on the blocks in the wing bay, (look out for any jumpers on those blocks, there were none originally) but this could be a complete red herring.

You will note that the fuel pump is fed from the input side of the fuse that feeds those switched circuits that are rather inadequately fused, so is not itself fused.

By the way my understanding from the diagram I posted is that all feeds from the switched fuse are green, it is the feeds from the un-switched fuse that are purple.

Good luck

[DODD]

David,

Thanks for your reply, the information you gave is the same as what I already have but my question is relating to a group of wires not connected to anything at the moment and all bound up together as a group with black insulation tape holding them all together.

These wires were connected or maybe they were intended to be connected to some equipment at one point; that is really what I am trying to find out. There is no trace of these wires in the vicinity of the fuse board or surroundings, they just disappear into the very chunky wiring harness behind the dashboard.
My ammeter is wired correctly, as is the ignition switch etc. and everything worked ok except the clock which had never worked. I sent the clock away for repair only to find it was a positive earth instrument which surprised me a little, but it is now repaired and working.

Roger’s post referring to a post he made in November 2019, whereby he attached a wiring diagram for the 410, clearly shows the white wire coming off the live side of the fuse and going directly to the fuel pumps. This will be my point of access to the wiring for the switching. (Thanks Roger for highlighting your old post.)

With relation to the SU Dual Action Fuel Pump: My existing pump died through old age and probably the addition of ethanol in modern petrol. I decided to buy a Bosch electronic inline fuel pump as a temporary measure, it works very well but I don’t like the whirring noise which is constant, I prefer the gentle tick of the SU Pump. I sent my old pump to a specialist for repair rather than buy new and even though I haven’t fitted it yet, I am very pleased with the appearance and I know it’s been pressure tested for compatibility with my Edelbrock carburettor, which incidentally I had tuned and calibrated by the same person before fitting. A few photos attached of before and after. (Only able to attach after photo)

Brian

[DODD]

Since my previous postings regarding these mystery wires; I have been thinking, as my 410 is an early series 410, these wires may be related to the push button gear change mechanism that was fitted to earlier models. They are in the right location of the dashboard and look big enough to control the various solenoid loadings.

Brian

[Roger Morrall]

Brian

That could well be the case. Especially if all else and the ammeter works as it should. I had a number of wiring diagrams, one of which I think purported to be for the 409, all of which are now with PEU186Fs new owner but I’ve never ever spotted one that included any details of the push button gear change mechanism. I wasn’t even aware that the early 410s retained it but one lives and learns. It also wouldn’t have been beyond Bristols to use a left over 409 wiring harness in a 410.

While you’re thinking about all this spare a passing thought for your ignition switch and the load it’s handling and marvel that it’s lasted as long as it has.

[DODD]

Roger,

I don’t think any of the 410’s retained the push button gear change and I also have no doubt that Bristol would have used all of the wire harnesses from previous models which they had in stock and quite rightly, as very little changed between earlier models.

Looking at the loadings going through the ignition switch gives me some concern. It is my intention when adding the isolation switch to the fuel pump, I will also be installing a relay and fuse to the circuit, this will be in addition to a few extra fuses as required.

Brian

[Sam410]

Originally Posted by DODD

Looking at the loadings going through the ignition switch gives me some concern.

To possibly fuel your concern, I have got through two ignition switches in the near 90,000 miles I have had my 410. The original (or at least the one fitted when I bought the car) expired around 12 years ago, its NOS replacement lasted about 8 years and I fitted a new replacement then. The modern one has one less terminal posts than the older design, so there was a degree of head scratching involved to work out which wires could be combined.

When they start to burn out there is an unmistakable fishy smell as the plastic of the switch overheats. The first one finally failed in France and I spent the next 1000 miles having to hotwire the car at every stop!

[Roger Morrall]

The load on the ignition switch is bad enough, consider also the back emf that is generated when a dc motor is switched off.

Having experienced an ignition switch failure I arranged for the switch to operate a very heavy duty relay which in turn fed the fuse that "protects" the green switched circuits directly from the brown battery circuits.

I also comprehensively increased the number of fuses so that each circuit was appropriately fused - which turned out to be the devil of a job, one that would have been very much easier if I could have had the car on a lift, but that’s another story.

My failed switch was I believe an original fitment and probably of much better quality than anything you’d find today. It’s failure pattern showed up through a very intermittent apparent misfire, initially so short that one hardly noticed, but the length of the misfire extended gradually over a period of several years until finally the car would come to a stop yet mysteriously would restart after a few seconds after the switch had cooled down.