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SP New wiring loom problems

gc0700
Posts: 82
Joined: Wed Sep 21, 2016 8:29 pm
Location: Bury St Edmunds

SP New wiring loom problems

Post by gc0700 »

I obtained a new wiring loom from David Manners - its made by Auto Sparks.
All installed, but am having some issues.
I'm using Positive Earth and I have a brand new, fully charged 60Ah battery.

In the boot, I'm only seeing about 8v, which is just about enough to make the tail & number plate lights glow, but apparently not enough to power the petrol pump. I've confirmed that the pump is working OK, by connecting it directly to a battery.

Checking further, with nothing connected to the battery, it's showing 12.46v across the terminals.
Having the battery earth wire connected and the other battery wire connected to the solenoid (but not to the battery), I'm seeing about 3.5v between the unconnected terminal and the solenoid wire (but no Amps being drawn).
Disconnecting everything but the battery wire from the solenoid, the volts drops to near zero - good.

The wire from the Solenoid to the fuse box, does not seem to be an issue - connected or not, the voltage remains about constant.
But the wire from the Solenoid to the Ignition Switch (terminal 1), does seem to be an issue. Connected at both end, I'm seeing about 3.5v, and more worryingly, with the Solenoid end connected and the Ignition Switch disconnected, I'm still seeing 3.5v (but no Amps). This wire goes via the Ammeter, so should that be losing me 3.5v?

Can I take the Ammeter out of the circuit, to see if I can get something working?

On the solenoid switch cable (from the Ignition Switch, terminal 3), I'm also only getting about 8v (not surprising, given the above), but that does not seem enough to actuate the solenoid, although I do hear a gentle "clonk", which actually seems to come when the key is released. The engine turns OK, if I press the button on the end of the solenoid.

Any ideas to resolve this would be much appreciated.
Tim

Ian Slade
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Joined: Sat Feb 13, 2016 9:54 am
Location: Sevilla Spain

Re: SP New wiring loom problems

Post by Ian Slade »

Disconnect everything from the battery and fuse box, start from scratch, connect +ve to a solid earth on the chassis, connect that earth to the engine, connect the -ve cable from the battery to the battery side of the starter solenoid, connect the other side of the solenoid to the starter motor. Press the solenoid rubber button or short across the terminals with a heavy duty insulated handle screwdriver if you do not have a button, the engine should turn. If not check the voltage from the engine to battery -ve, if not 12.4 volts or above check from chassis earth to -ve terminal for 12.4 volts, you should have 12.4volts in one of those checks. Should the engine have turned in the first check the add -ve wires one by one checking each function. If you don't succeed post again stating where the failure occurs. Should the engine not turn check for zero Ohms from any chassis point to the engine not using your earth connections, if you don't have zero Ohms you have an earth connection problem, not unusual if the chassis has been painted or there is rust present.
Owner since the 70's, Genghis is slightly to my left.

gc0700
Posts: 82
Joined: Wed Sep 21, 2016 8:29 pm
Location: Bury St Edmunds

Re: SP New wiring loom problems

Post by gc0700 »

Hi Ian,

Very many thanks for your input.

As I mentioned in my post, the engine will spin if I manually press the button on the solenoid.

But one thought on the solenoid, there is no marking to indicate which side goes to the battery and which to the starter motor - does this matter? I've tried it both ways around, with no disernable difference.

You have reminded me, I do need to look at the chassis earth, which I'll attend to in the morning and report back.

Thanks
Tim

Ian Slade
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Location: Sevilla Spain

Re: SP New wiring loom problems

Post by Ian Slade »

Doesn't matter on the solenoid, if the engine spins OK check the chassis earth, obviously the battery to engine earth is OK, seems as though the battery chassis earth is poor.
Owner since the 70's, Genghis is slightly to my left.

gc0700
Posts: 82
Joined: Wed Sep 21, 2016 8:29 pm
Location: Bury St Edmunds

Re: SP New wiring loom problems

Post by gc0700 »

Ian,

Adding a link between one of the loom earth terminals (on coil or solenoid) and the engine or chassis earth points, seems to have solved my issues. Exactly as you were indicating.

Not everything is yet connected to the loom, but what is connected, is working as expected. Engine now starts on the key and runs OK.

Many thanks for your guidance.
Tim

Zbigmak
Posts: 63
Joined: Sun Nov 19, 2017 10:45 pm
Location: Warsaw Poland

Re: SP New wiring loom problems

Post by Zbigmak »

Gentlemen
Continuing the discussion. I am also in the process of rewiring my Dart. I am finding it difficult to figure out how and where all the earth connections go. I am running positive earth. The + battery terminal is connected to the top of the engine block. There is also a large spade connector on the block connection which at present has no wires connected to it. The gearbox has a earthing strap to the chassis.
The instrument panel seems to be missing a suitable earth connection.
Can anyone assist me in trying to master the art of earthing all the individual components.

gc0700
Posts: 82
Joined: Wed Sep 21, 2016 8:29 pm
Location: Bury St Edmunds

Re: SP New wiring loom problems

Post by gc0700 »

My positive battery terminal is connected to the engine bellhousing. And there is a further connection from the bellhousing to the chassis. So all much the same as yours.

The new loom has many earth connections (all Black wires on my loom). For the instrument panel section, there is a small sub loom for the instrument illumination, that has bulb holders and earth wires with small eye connections for the mounting bolts of each of the 6 instruments.
Although looking at my old loom, I don't see all the corresponding earth connections. So mybe the new loom has this as an enhancement?

And as mentioned on my previous post, the are also earth eye connections to earth the coil and solenoid. And as I've now found out, one of these needs to be connected to the chassis or engine.
Tim

Sydsmith
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Location: Aberystwyth Wales

Re: SP New wiring loom problems

Post by Sydsmith »

In DC electrics there always has to be a positive and negative feed to what ever you are intending to operate.

In a conventional metal bodied vehicle that is fairly easy to achieve. The metal body is used as either the positive or negative lead and is commonly called earth. The other feed is provided by individual cables to each item that requires 12 volts, the item say the fuel pump has another lead connecting it to the body or chassis. We won't go into the reason why there have been changes between positive and negative earth vehicles over the years, suffice it to say either will do.

The SP has a special problem in that it has a glass fibre body which as it is a good insulator will not of course conduct electricity, so cannot be used as the second lead. To provide the necessary second lead or earth, there needs to be special arrangements in the wiring loom to ensure an earth is available throughout the wiring system where it is needed. If you don't understand electrics and are fitting a new loom for the first time, it does not get much more difficult than a glass fibre vehicle.

In the case of a positive earth vehicle, the positive battery terminal is connected directly to the chassis and the engine block and drive train are also connected either directly to the positive battery terminal or via a thick lead to the chassis.

So in an SP250 wiring loom as you have discovered bigmak you are going to find lots of earth leads to make up for the lack of a metal body. On the SP there are common points for the earth connection and they are and several can be bunched together on one point and an earth return taken back to a central earth or to the chassis.

I don't have my SP wiring diagram to hand but from memory you will see there are several leads the connect to the chassis at the front and back end of the vehicle. Hope that helps. Syd

Ozzsp250
Posts: 284
Joined: Tue Feb 16, 2016 12:35 am
Location: Arizona, USA

Re: SP New wiring loom problems

Post by Ozzsp250 »

On my car 2 large brown wires with spade connectors are on the starter solenoid [probably 10 gage wiring in USA speak]. On the wiring diagram attached, one shows going direct to the ammeter. The wiring diagram shows from the ammeter another large brown goes to the horn circuit, however I believe on my car the second large brown connection at the starter solenoid goes directly to the horn circuit.

I'm not able to follow the wires today but will do tomorrow if it would help.
Attachments
Daimler_SP250_WiringDiagram_v2.pdf
(1 MiB) Downloaded 102 times

Sydsmith
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Location: Aberystwyth Wales

Re: SP New wiring loom problems

Post by Sydsmith »

Thanks Denis, the diagram shows the large number of connections that need to find their way to earth for the different units on the car. As I said earlier, on a metal body car that is very simple jusst bolt it onto the body or chassis, on a "plastic" car body alternative arrangements have been made during manufacture and with the wiring loom. Syd

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