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Wiring an old single-seater

Practical Motorsport Wiring - Club Level

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Hi, I’m planning to re-wire an old single seater race car. As you can see from the diagram, there aren’t too many components, but this will be my first loom, so could anyone sense check this for me?

Can anyone also advise whether it’s better to join the wires from the Coil and the Fuel Pump into a single wire to go to the Ignition Switch? And similarly, if it’s better to splice the 3 Ground wires and run a single wire to the Engine Ground.

Thanks in advance

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The master switch should be between the ignition switch and battery, preferably between the battery and starter so ALL power is cut.

You don't have any fuses, fit a simple fuse block near the battery +ve terminal and, at a minimum, run one fused link to the ignition and, preferably, the relay you're using for the fuel pump, as mentioned below.

Back in the day, it was common practice to ground the fuel pump through an oil pressure switch, so if the engine stops the fuel pumps shut off because there's no oil pressure. This may need a relay to minimise the current through the switch. If you look at old racecar films and videos, you should see something like "Pumps On",s or "Pumps Off", written on the dash with a toggle switch or two above or below it - this/these are a separate ground for the fumps used when priming/starting the engine when there's no oil pressure and it's to remind the driver to turn the switch(es) OFF when the engine starts - certainly before leaving the pits, so the pump(s) don't keep pumping fuel into a potential fire.

Thank you for the comments. That's really helpful and I'll have a bit of a think about how to ground the fuel pump.

It's been a while, so forgot to mention it's a pressure operated (closed) switch, rather than the common warning light switch that is opened by pressure.

Some pressure switches are fitted with two terminals, one normally open, one normally closed. These should allow you to use it as a relay ground and also have a warning light - if you're using a mechanical gauge, you need to look at it, but with a light you will be more likely to catch a flash if the engine loses oil pressure mid-corner, or under heavy braking.

However, if you use a 5 pin relay you could use the common type if you take the power to the pump from the 87A terminal.

May I ask what the project car is? Sounds like something cool :-)

Thanks for asking… the car is a 1958 Cooper-Climax. I’ve attached a couple of photos.

At the moment I’m leaning towards wiring without the pressure switch on the fuel pump. I’ve been racing for a long time and never had this set up before. I can see it’s safer, but if I can’t switch the Master off, that implies a big impact and in that case I’d probably be in trouble with or without the switch.

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Not just cool, but very cool!

Well, if you're knocked out, or stunned, and can't turn it off manually, if the engine stalls it'll shut the pumps off - I'd say that was the reason they were used.

Your call, though - just check with the scruiteneers, they can be funny sometimes.

Thank you. As you say, it's a cool car and such a joy to play with. Following on from previous posts. Is the attached looking ok?

For context, I have a nice, professionally made loom in the car. However, when it was made, I wanted the option to run replica electronic gauges an external fire button etc. The problem with this is I’ve got lots of redundant wires and so I want to make something simpler and neater, keeping the current loom as a spare. The current loom doesn't have the oil pressure switch and I've never had a car that does. The scrutineers have been happy so far...

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Yes, I would expect the period instruments to be mechanical, they should still be available but the capilliary tubes are a ****ing PITA and electical are much easier to fit.

It always amuses me that that engine was first developed for a fire engine pump - a real 'Cinderella' engine. For those unaware of the engine, and it's history - https://en.wikipedia.org/wiki/Coventry_Climax

The fuse and master switch need to be swapped, if the master has the current rating to take it, you can put it between the battery and starter power, with the rest of the circuit fused from the switch, if you have the battery to the starter and the master off the starter, the fuse can be placed between them - as a general rule the fuse is places as close tot he power source as practical, because it protects more of the circuit.

Convention has secondary wires that come of a main wire coming off as a "T", or when the same terminal is used the two (or more) wires are shown coming off the same point as you have with the battery - when you dont, like the starter switch, it looks like you're using 3 different terminals, rather than the two.

On that, the way you have the starter switch between the', corrected, 'master' switch and ignition switch it will be possible to crank the engine with 'master' on and 'ignition'off - this can be useful if the engine has a tendency to 'kick back' when initially cranking - you can spin the engine before tuning on the ignition and the inertia can more easily overcome the resistance of the ignited gasses. A friend used this for a high compression engine with a lot of initial timing and it made a BIG difference.

More conventionally, take the feed for the starter button from the ignition out, this means you can't accidentally crank the engine by hitting the switch with ignition off.

Thank you so much for the comments. It’s really helping me piece things together.

The period instruments are available, but some items are more available than others and so it’s taken me a bit of time so sort these out. It’s all part of the process though and just lovely to share a passion for old racing cars and learn some interesting stuff.

As you say, the Coventry Climax engines were pretty special and even though ours is in early 1958 (2-litre) spec, in a 500kg car with skinny tyres, it feels quick.

With regard to the wiring, I’ve got the battery to the starter and the master off the starter, so I’ve now put the fuse between them on my diagram. I’ve also shown the wires coming off the battery as a ‘T’.

I did want the starter button to bypass the ignition switch. I like to crank the engine for a couple of seconds to build oil pressure before flicking on the ignition and starting it. It strikes me as a bit kinder to the engine and it may help me spot a problem early if I have one.

Thanks again for your help – it’s really appreciated

Hi, apart from some ring terminals, my planned wiring loom has only 3 connectors to consider... and on the existing loom, 2 of them are the same 1-way, plastic things in the photos. As the female end on the starter motor looks to be integrated, I'd prefer to use that and so need to find a male end that fits. It looks like my fuel pump uses the same connector, so for simplicity I'd planned to go with what's there too.

Can anyone help me identify what they are and where I can buy them? I’ve spent a fair bit of time Googling, but must be using the wrong search terms.

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I think what you're looking for is an insulated spade terminal cover. Looks like you need one that latches or locks.

Thank you, much appreciated


take a scroll through this, most likely they have replacement terminals and housings.

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