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Hi,

Had my TomTom hardwired into my 2019 mk8 Vignale today. It was wired in so power only in to TomTom when ignition is on.

I already have a dashcam fitted  a while back by the same firm.

As soon as I drove off, my Fiesta started to show weird behaviour, never witnessed before.

It was like someone had filled the tank up with Kangaroo juice, and the power of the engine seemed to be reduced.  So I pulled into sideroad powered off ignition and it seemed much better when I restarted, then I noticed the warning light yellow car with swerving lines under it, my Ford app messaged me to say it had a Powertrain fault.

Took my car back to the fitter, and left it with them for 40 minutes, when I got back they told me they had wrongly piggybacked off a fuse they shouldn't have, and now they have connected it to a fuse which makes the wire to the TomTom live all the time.  So I now just have to make sure the display is off if ignition is on, so as not to drain the battery.

Can anyone shed any light on the technical  viability of this whole event, and the methods the fitter has employed to rectify the problem.

It behaved OK when I drove back, and I asked if they had disconnected the battery at all as I know this can cause errors, they hadn't disconnected the battery, or even lifted the Bonnet.

Cheers

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Luke is right, so long as the piggyback fuse holder is in the correct way then the circuits remain seperate. If its in the wrong way the the current draw for both circuits will go through one fuse first and then the added device will also then draw its current through the second fuse - in effect the fuses are in serries. Its not a big issue if its wrong so long as the fuse supplying both circuits is of a high enough value, but its not good practice and not recommended.

There are plenty of ignition controlled circuits/fuses in the fuse box of the fiesta, it is normal to piggyback off the fuse for the radio.

Switching off the screen on your dashcam is probably doing just that, your dashcam will still be live and draining your battery.

I would say you need to get it sorted.

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Hi CSC, no real change. For the small amout of current the dashcam uses and the small amout of current the TomTom uses they could both share the same switched ingnition live circuit.

Use the one piggyback fuse that is suppling your dashcam if that is ignition controlled and just connect the supply for the TomTom to that. The two items together will be less than 3 Amp and I bet the fuse in the piggyback is higher than that.

Remove the piggyback fuse holder for the TomTom its not needed. Remember to replace the original fuse back in the fuse box

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Many Thanks unofix, will do

Thanks for your quick help, much appreciated 🙂

PS do you think that powertrain fault was related to this and are there any potential problems here?

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I can guess what they did. There is a fuse in the Fiesta that controls the Powertrain (7.5 Amp) might be fuse 22.  If you remove that fuse when the ignition is switched on then all hell breaks loose. It's not an ideal fuse to mess about with. If it does get removed then to clear the many problems that 'Pop-Up' the ignition needs to be switched off and then sometimes the car left for 30 minutes before restarting. That will normally clear the faults (provided the fuse was put back).

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Thanks Luke, when you say remove bottom fuse, not sure which one..sorry

Or do you mean the fuse under the piggyback? I just pulled out the right hand spur, and noticed 2 fuses one had a 20 on the back, the other didn't really have a number.  Do I take out 1 or both? To perform the test

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Each piggyback has 2 fuses; the original one for the circuit you tapped off, and the new one for whatever you're adding on. Remove this fuse on each piggyback. piggy-back-fuse-holder_1_1.thumb.jpg.621e988dfef3bcc064784ace15f14982.jpg

Ive attached a wiring diagram to explain the reasons. Imagine you swap points A and C, the current then flows through both fuses to get where it needs to go, meaning you could potentially blow the lower fuse if you pull too much current on both circuits at the same time.

Hence why I said the easiest way to test it is by removing the lower fuse, therefore you know whether the current is passing through fuse 1 to get to fuse 2.

hbocj5iglal21.thumb.png.2a381da507b596194dd33202d3b1f8b8.png

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1 hour ago, Chainsawcharlie said:

20210414_184232.thumb.jpg.cb7cb82a5abcdfcf02ef5f39962cfee5.jpgJust taken this photo of the fuse box, both fitted by Halfords.

Piggyback on left is dashcam

Piggy back on right is TomTom.

Unfortunately this is beyond my scope

20210414_184221.jpg

Without looking, I can’t remember which fuse I used for my dashcam, but it looks like the Tomtom is using a spare fuse location, but like Luke said fuse looks to be upside down. There’s no reason why your dashcam and Tomtom can’t share the same supply, as the current draw will be small, even with both on together. However this needs checking, as it doesn’t look like your Tomtom feed is protected by a fuse.

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8 minutes ago, Jollyandy said:

Looks like the Tomtom is using a spare fuse location, but like Luke said fuse looks to be upside down. This needs checking!

Cheers Andy, its looking that way, yes you're right after looking on various sites it does appear to be a spare unused 20ampwill check it out tomorrow

Cheers

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14 minutes ago, Luke4efc said:

Each piggyback has 2 fuses; the original one for the circuit you tapped off, and the new one for whatever you're adding on. Remove this fuse on each piggyback. piggy-back-fuse-holder_1_1.thumb.jpg.621e988dfef3bcc064784ace15f14982.jpg

Ive attached a wiring diagram to explain the reasons. Imagine you swap points A and C, the current then flows through both fuses to get where it needs to go, meaning you could potentially blow the lower fuse if you pull too much current on both circuits at the same time.

Hence why I said the easiest way to test it is by removing the lower fuse, therefore you know whether the current is passing through fuse 1 to get to fuse 2.

hbocj5iglal21.thumb.png.2a381da507b596194dd33202d3b1f8b8.png

Having looked at the diagram, I get it now thanks Luke.

True what they say a picture is worth 1000 words.....especially in my case 🙂

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The problem is that you went to Halfords who did not disconnect the battery while working on a customer's electrical system. That is professional negligence and not unexpected from Halfords, unfortunately.  A proper auto electrician would have done a proper job. (or you could have used Cyanlabs for free...)

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3 hours ago, unofix said:

Hi CSC, no real change. For the small amout of current the dashcam uses and the small amout of current the TomTom uses they could both share the same switched ingnition live circuit.

Use the one piggyback fuse that is suppling your dashcam if that is ignition controlled and just connect the supply for the TomTom to that. The two items together will be less than 3 Amp and I bet the fuse in the piggyback is higher than that

So I would be able to add the piggyback connector of the tomtom to one of the empty fuse sockets of the dashcam?

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Hello CSC, first I would just like to say Luke has done an excellent job of explaining the situation. Many years ago when I first came across these piggyback fuse holders I realised then the potential problems with using them. First unless you can test which side of the exsisting fuse is the supply side and which side is the load side you can't know which way round to fit the piggyback fuse holder.

In answer to your question, not all of the empty spaces will have a supply. Next if you find an empty space with a supply you will need to establish if the supply is on all the time (not what you want) or if it is switched via the ignition.

(1) What I would suggest is remove the piggyback adapta for the TomTom. Put the original fuse back in the fuse box.

(2) Next remove the piggyback fuse adapta from the end of the TomTom wire and get rid of it.

(3) Now pull the piggyback adapta for the dashcam from the fuse box. The piggyback adapta is joined to the dashcam wire by a blue crimp. Cut the crimp off both the piggyback adapta and the dashcam wire.

(4) Next strip the end of the dashcam wire and the TomTom wire and twist together. Now strip the end of the piggyback wire. Get a new Blue crimp (Halfords sell them 🤣) and put the dashcam/TomTom wires in one end and squeeze the crimp closed. now in the other end of the crimp put the wire from the piggyback adapta and squeeze the crimp closed.

All done. You now have one piggyback fuse adapta ready to supply both devices. Put the piggyback fuse adapta back in the fuse box where it was for the dashcam.

Thats you finished. The dashcam and TomTom will share one of the fuses in the piggyback adapta, and the original circuit will have its own fuse. Sorted !!

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1 hour ago, anon said:

The problem is that you went to Halfords who did not disconnect the battery while working on a customer's electrical system. That is professional negligence and not unexpected from Halfords, unfortunately.  A proper auto electrician would have done a proper job. (or you could have used Cyanlabs for free...)

Thanks, next time I will use Cyanlabs to fit my TomTom satnav 🙂

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Thanks Unofix  for taking the time to explain, armed with what both you and Luke have supplied I should have no excuse now.  Thats my job for tomorrow 🙂

cheers mate

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1 hour ago, unofix said:

Hello CSC, first I would just like to say Luke has done an excellent job of explaining the situation. Many years ago when I first came across these piggyback fuse holders I realised then the potential problems with using them. First unless you can test which side of the exsisting fuse is the supply side and which side is the load side you can't know which way round to fit the piggyback fuse holder.

In answer to your question, not all of the empty spaces will have a supply. Next if you find an empty space with a supply you will need to establish if the supply is on all the time (not what you want) or if it is switched via the ignition.

(1) What I would suggest is remove the piggyback adapta for the TomTom. Put the original fuse back in the fuse box.

(2) Next remove the piggyback fuse adapta from the end of the TomTom wire and get rid of it.

(3) Now pull the piggyback adapta for the Dashcam from the fuse box. The piggyback adapta is joined to the dashcam wire by a blue crimp. Cut the crimp off both the piggyback adapta and the dashcam wire.

(4) Next strip the end of the dashcam wire and the TomTom wire and twist together. Now strip the end of the piggyback wire. Get a new Blue crimp (Halfords sell them 🤣) and put the dashcam/TomTom wires in one end and squeeze the crimp closed. now in the other end of the crimp put the wire from the piggyback adapta and squeeze the crimp closed.

 

Thanks mate, when I do this will I still need to establish if the fuse for the dashcam is in the correct way round?

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It would be best to establish the correct way.

When you are ready to put the piggyback adapta back in to the fuse box do not fit both the fuses. Only fit the top fuse (3 or 4 Amp), that is the fuse that is lined up with the red wire. Plug the piggyback adapta back it to the fuse box - turn on the ignition and see if the dashcam and TomTom work.

It is fair to say that something or things will not be working on your car because the second (bottom) fuse is not yet fitted. If the devices are not working take out the piggyback adapta anrd rotate it 180 degrees and plug it back in and try again.

Once you have established the correct way it needs to be fitted in order to get the dashcam/TomTom to work then take out the piggyback adapta one last time and fit the second fuse (bottom) then plug it back in. All should be well with the world 😀

If after all this you have some random warning lights don't panic. Switch off the ignition, go and make some coffee and try the car again in half an hour, it should have reset.

 

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2 hours ago, anon said:

The problem is that you went to Halfords who did not disconnect the battery while working on a customer's electrical system. That is professional negligence and not unexpected from Halfords, unfortunately.  A proper auto electrician would have done a proper job. (or you could have used Cyanlabs for free...)

Disconnecting the battery isn't really necessary. As useless as Halfords is, calling it "professional negligence" is a bit extreme.

The circuit is dead until you plug in the fuse tap (which is the last thing you do). You wouldn't disconnect the battery when plugging in the micro-usb which is no different to plugging in the piggyback. Sure, you disconnect it when unplugging the radio for example, but not for putting fuses in and out.

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