UKC

I don’t understand how the Apple USB cables work as there are 8 or 16 connections at one end but only 4 at the other. I have to connect my phone by its USB cable to the connector in the car to use the Apple car play with certain apps. This works fine until I try to use a cable splitter to give me another outlet. The splitter is just 4 pins to 4 pins as far as I can see but won’t let the Car Play work. Does anyone know what’s going on please? Normal phone workings work fine on Bluetooth. 

Is the splitter Apple MFi certified? You might have to pay Apple tax for it to work. 

Besides the above comment about being an Apple certified splitter/cable etc, check if your splitter is made to work in the direction you are trying to use it (assuming it’s not a dual direction one).

Just a thought to check as I discovered last year some (most?) splitters sold for certain purposes are made to work in one direction only for full functionality and if you are trying to use it in reverse will not properly work if it works at all.

As far as I know carplay requires a direct connection - some sort of safety control. 

Using the splitter doesnt give a direct connection.

Never bought into Apple as a brand, but Android auto only works with certain leads - they need to be (usually branded) syncing not just cheap charging leads. 

Thanks for the replies. I understand that the phone needs to talk to the display and this works ok on the normal Apple charge cable. What puzzles me is that the splitter cable is a straight through 4 pin connector as is the usb end of the Apple cable and also the car socket.

Android would work via Mirrorcast but this is another can of worms.

I’m confused a bit by your terminology. One end is (presumably) USB-A, and the phone end is Lightning (an Apple proprietary plug, looks a bit like USB-C).  Splitters usually struggle to transmit data (as you need) but are generally ok for power (albeit at low wattage). I think it’s a USB issue, USB standards are still pretty Wild West for something that’s meant to be a universal standard. See also HDMI. 

b

Yes the phone cable is USB-A to Apple lightening. The first confusion (to me) is that it is 16 pins at the phone end to 4 pins at the USB-A end. Therefor I would have thought that continuing the 4 pins, as the splitter cable does would make no difference.

I can understand your logic with counting the number of pins but I don't think it actually indicates very much. The connectors at each end of the cable will be standard but you can't see which pins are actually connected inside the cable. From a quick Google, most Lightning splitters will be power only, a few will do power and audio, but it's not clear that what you're looking for actually exists at all. I'd be surprised if it did. It's a fairly niche use case and would be complicated to make (probably requiring signing up to Apple's hardware developer program and paying expensive testing fees), if it's actually feasible at all.

You probably need to consider a different option for whatever you need the other half of the splitter to do. Power the other device from a charger in the cigarette lighter socket? Check whether your car has another USB socket hidden away somewhere?

Thanks for the reply. I’m not stressing over this and can see that I’m not going to get what I want. Unfortunately my car only has one USB port and it is in place of the cigarette lighter socket. There is a cigarette lighter socket hidden inside a centre console but with no way without modification to bring the wires out.

What annoys me slightly is I recently hired a small cheap car in Spain that ran Apple car play via Bluetooth.

I don’t think you will ever get data up and down a cigarette lighter socket. Did someone do an aftermarket wired replacement of your existing fag lighter so it is a USB-A socket wired to the head unit? That’s really handy if so.
Standard fag lighter holes just do power - I just have a fag to usb converter in the arm rest and run a spare power only iPhone cable out the door so other people can charge. 
I think your hire car experience shows the difference between wireless CarPlay and wired CarPlay. This is a limitation of the cars system rather than the phone, my 2017 Skoda for instance does wired but not wireless; this last month I have driven four different hire cars and only one had wireless CarPlay. More recent vehicles may have wireless on their units but not always. 
There are wireless CarPlay adapter units out there that you can plug in to the USB socket but they won’t charge your phone at the same time, unlike plugging it in. I think there is some detail about the adapters on the Macworld website but they are very model specific and tbh I haven’t summoned up the strength to bother trying! 
hope that helps

cheers

b
 

Ok I have finally understood your original question - am slow on the uptake!

Your car only has wired CarPlay, the hire car had wireless CarPlay. You can get an adapter to make wired wireless - but it still connects to the usb, only now your phone doesn’t charge. There is no way to have two data connections in your setup, but you can always charge from a usb dongle plugged in to your fag lighter in the arm rest. 
Retrofitting an extra usb connector would need an auto electrical bod and the head unit on your car may not be able to reliably decide which phone to connect to. 
Hope that makes sense

b