Decided to add digital speedo/tack anyone do it?

[RG68RG]

I guess what I need to know from people who may have done it is this.. Can I just connect the wires on the new digital unit directly to the old ones coming out of the tach etc? Meaning.. The ones that correspond to the things they power like (tach) Oil, battery indicators etc ..could i just cut these, and connect them directly to the new unit? If this is the case I'm fairly sure even the electrical idiot like myself could do it. Any info would be greatly appreciated as an unlit and non functional tach and speedo that's way off, are driving me nuts.   

[Justin B.]

It depends on the unit.

[RG68RG]

It depends on the unit.

I was hoping someone that had put one in could give me some insight actually..

[wilcom]

It depends on the unit.

I was hoping someone that had put one in could give me some insight actually..

If you search our forum for "acewell" you will get back a ton of information on the subject.

[Adrian]

Hi - I have successfully fitted an Acewell 2835 speedo/rancho unit. I have all the info for fitting it at home which includes the wire colour conversion . I would be happy to share everything I have.
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I used small connector pins to fit tonthe original plug that fits into the back of the tacho o. Everything works fine including the tacho by connecting directly to the black wire in the plug.
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So if you PM me your email I will send it all to you [ch128077][ch128521]
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This is before I tidied everything up to cover the gap.

[tiggum]

Installed into an R65LS at that!  Nice job; please show us the finalized version.

[RG68RG]

Hi - I have successfully fitted an Acewell 2835 speedo/rancho unit. I have all the info for fitting it at home which includes the wire colour conversion . I would be happy to share everything I have.
.
I used small connector pins to fit tonthe original plug that fits into the back of the tacho o. Everything works fine including the tacho by connecting directly to the black wire in the plug.
.
So if you PM me your email I will send it all to you [ch128077][ch128521]
.
This is before I tidied everything up to cover the gap.

If I go with that unit I will for sure!!   I'm still sifting through all the different digital speedometers out there right now. BTW..Is the red bulb in the center of the old console for the generator? I keep reading that the micro electric warning lights on these digital speedo's won't complete the circuit to allow the battery to charge..

[Adrian]

Yep that's correct - I instAlled a resistor in circuit to produce the sAme resistance effect as the original lAmp - otherwise the system won't charge the battery. I put the red LED there just cos I like to see a red light go out when started - the LED doesn't actually help with the charging circuit. I have the info for fitting the resistor as well. A very simple process.

[Adrian]

Installed into an R65LS at that!  Nice job; please show us the finalized version.

Here is the finished item - I used two wooden lids from storage jars to fill the empty holes - I have a digital volt meter for the left hand side - I'll be drillin a hole in this one with my circular cutters, Pictures below

[Tony Smith]

I recently bought a dead speedo and sent it and my recently purchased Chinese GPS speedo to an instrument shop to have the two married.

I'll let you know how it works out.

[Adrian]

I recently bought a dead speedo and sent it and my recently purchased Chinese GPS speedo to an instrument shop to have the two married.

I'll let you know how it works out.

I checked the GPS speed app on my phone against my car speedo a while ago - the App was readin as much as 10 kph below the car speed at less than 70 kph - I was told that it's due to the time lag between satellites - any thoughts about that mate

[Tony Smith]

I checked the GPS speed app on my phone against my car speedo a while ago - the App was readin as much as 10 kph below the car speed at less than 70 kph - I was told that it's due to the time lag between satellites - any thoughts about that mate

Sure have, but you are not going to like it - simply put your speedo is wrong. First of all, manufacturers deliberately make speedos optimistic, this is to give them wriggle room to avoid being sued after you get booked by the Police.

Second of all, your car speedo is dependant on the tyres you have fitted being an exact match in rolling diameter for the ones fitted as OEM.

Third of all, whilst radio signals only travel at 186,000 miles per second the GPS satellites are a mere (approximate) 12,500 miles away. all GPS satellites operate on a common clock so that the GPS system automatically compensates for signal propagation delays, when you think about it, it has to be that way as the military users of the non degraded signal can stuff a cruise missile into your letterbox and surveyors using differential GPS (a clever commercial way of getting around military "selective availability" degradation achieve 5mm accuracy.

Frankly I am not at all surprised at a 10kph error in your speedo, many are far worse than that.

[wilcom]

I recently bought a dead speedo and sent it and my recently purchased Chinese GPS speedo to an instrument shop to have the two married.

I'll let you know how it works out.

I'm getting ready to change the 85mph speedo on my 84LS and will be on the edge of my seat waiting for that report!

Cost is a factor and since you are having them "married"..... we all know how much that costs!

[georgesgiralt]

Hello,
First, as far as I know, the US Gov has allowed every one to use the full precision on GPS satellites. i bet they have a tenfold acurrate replacement or worse ;-)
Next, your GPS using application is not perfect because it calculate your position at intervals. And devise speed using a right line between positions fix. So if you are on a straight line of travel, the GPS using app will give a speed which can be checked against your speedo which measure the number of rotation your tires made...
Last but not least, here in Europe car makers are legally bound to have speedo indicating a speed which will never be less  than the actual speed. So they err on the safe side and provide way less tolerance they can do....
I've checked my speedo when new at being exact at 115 km/h (because I got a speed ticket ...) and recently after more than 30 years on the speedo with a GPS app on a 50 km straight road at less than 5% error... I think Motometer did quite a good job at accuracy if not at longevity ... 
There are, of course, specialized devices using GPS to calculate accurate speed by making GPS fixes at very rapid interval in order to reduce the strait line interpolation error.

[Tony Smith]

First, as far as I know, the US Gov has allowed every one to use the full precision on GPS satellites. i bet they have a tenfold acurrate replacement or worse ;-)


I was wrong by 18 years.....Which show how much interest I've had in the "mechanics" of GPS since I stopped flying.

https://www.gps.gov/systems/gps/modernization/sa/

Next, your GPS using application is not perfect because it calculate your position at intervals. And devise speed using a right line between positions fix. So if you are on a straight line of travel, the GPS using app will give a speed which can be checked against your speedo which measure the number of rotation your tires made...

Actually, most mobile phones have solid state accelerometers built in, as do all GPS speedos of any quality. During loss of signal events the accelerometers are used to provide more or less continuous speed update.

To the extent that geometric error is a problem it is greatly reduced, and in fact reduced to insignificance, as soon as the GPS device has fixes with three or more satellites - preferably not ones low on the horizon. If you have an Android phone, download and install the the app "GPS Toolbox" which aside from confirming the existence of accelerometers and roll/yaw axis sensors in your phone (and even a flux gate compass on the fancier ones) will show you how many GPS satellites it is receivign signal from. I went to my back deck and even with the metal roof occluding a significant part of the sky withing a couple of minutes my phone had a lock on 7 GPS satellites. Even my very cheap Chinese GPS speedo has accelerometers fitted and claims to be able to lock to a maximum of 12 satellites and to achieve lock on at least 3 satellites (to provide a reasonably accurate speed indication) within 20 seconds.

Last but not least, here in Europe car makers are legally bound to have speedo indicating a speed which will never be less  than the actual speed. So they err on the safe side and provide way less tolerance they can do....
I've checked my speedo when new at being exact at 115 km/h (because I got a speed ticket ...) and recently after more than 30 years on the speedo with a GPS app on a 50 km straight road at less than 5% error... I think Motometer did quite a good job at accuracy if not at longevity ... 
There are, of course, specialized devices using GPS to calculate accurate speed by making GPS fixes at very rapid interval in order to reduce the strait line interpolation error.

I didn't bother hunting the exact Australian Design Rules, however here is an interesting page from one of the larger motoring organizations here. My understanding is that the ADRs were changed in 2006 too align with the European rules, if that is correct then your understanding of those rules is not quite correct.

https://www.racq.com.au/cars-and-driving/safety-on-the-road/driving-safely/speedo-accuracy


Lastly, apparently there are many ongoing arguments on the accuracy of vehicle speedo as opposed to GPS devices. Here is a reasonably authoritative  article on the topic

https://www.geotab.com/blog/the-need-for-speed/