14 replies to this topic

[TehMarchant]

Okay so I won this tacho on eBay for £9 including postage and it wont work in my mini as it is positive earth. After some researching I have come to find I can just take it apart and switch it around.

 

 

 

 

Now the problem is that I have a 78 and these were ruled out in 72, will this still work for my mini as I still have points and condenser.

 

And how will I wire this bad boy up?

 

 

And if I just tried this without switching the earths around (may already have been done) what is the worst that can happen?

[cal844]

if you dont change the earths it will destroy various parts in the guage

[TehMarchant]

if you dont change the earths it will destroy various parts in the guage

It doesn't seem like the internals can be removed, can I just wire it up backwards?

[cal844]

i have no idea how to change the earths unfortunately! sorry

[TehMarchant]

i have no idea how to change the earths unfortunately! sorry

Okay no worries, anyone else able to give me some help please.

[KernowCooper]

No mate not suitable for your mini if its negative earth and it wont work wiring up in reverse, speedy cable can overhaul it for you but with conversions about £100, polish it up and use it for a paperweight.

 

I have one a negative earth one I took out of mine as its like all the rest of the 40yr old ones decay of the electrical components which make the tacho jump about over a 2000rpm band when changing gear.

[TehMarchant]

No mate not suitable for your mini if its negative earth and it wont work wiring up in reverse, speedy cable can overhaul it for you but with conversions about £100, polish it up and use it for a paperweight.

 

I have one a negative earth one I took out of mine as its like all the rest of the 40yr old ones decay of the electrical components which make the tacho jump about over a 2000rpm band when changing gear.

After reading this I was lead to believe that if i just wired the negatives into the positives it would work? http://mk1-performan...ths_tacho_2.jpg

 

Or have I just completely misunderstood this gibberish?

[Vipernoir]

It is possible to use the wrong polarity gauge in a car - I've done it.

 

You need to ensure that the body of the rev-counter is COMPLETELY electrically insulated from the car, without any part of it touching anything metal at all (I mounted mine in a wooden dashboard), and then carefully wire it up the wrong way round with the rev-counter earth going to live, and live going to the car body.

 

Worst thing that can happen ?
You've spent £9 on something that doesn't work anymore...

[TehMarchant]

It is possible to use the wrong polarity gauge in a car - I've done it.

 

You need to ensure that the body of the rev-counter is COMPLETELY electrically insulated from the car, without any part of it touching anything metal at all (I mounted mine in a wooden dashboard), and then carefully wire it up the wrong way round with the rev-counter earth going to live, and live going to the car body.

 

Worst thing that can happen ?
You've spent £9 on something that doesn't work anymore...

That was kinda my plan I just wanted to know if it may work on paper and a way to make it a safer option.

 

So I guess the spade would become the negative earth but then where would I attach the positive to?

[Tamworthbay]

Wherever it would normally positive earth - most likely the casing if there is no terminal marked up

[KernowCooper]

Ok I Just dug out the data I have on the 4inch O.E Smiths Tacho and the one in the picture is a O.E Most likely from a MGB.

 

The 4" RVI Rev Counter for positive earth vehicles came in 2 O.E styles

 

1. The (64-67yr)  RVI Positive Earth with a White Inductive Loop through a plastic clip on the rear which can be modified to work on a Negative Earth Car as per the after market Instructions above and also by opening the case and swapping the connections

 

The (68-72yr) RVI Positive Earth had no external White inductive loop and was designed with a inductive pickup inside and is not designed to read with the wires swapped around, they may show some indication of revs but can be +/- 2000rpm.

 

Not being rude when I say this but the rev counter in the OP picture needs a total refurb and no one would put it in there car surely even if it worked?

 

Mine I took out is immaculate compared to the one in the picture above but even RVCs are 40yrs old and read all over the place like mine when going through the gears (Bouncing needle ) stabilizes when constant revs, Speedy Cables can referb them but it £100ish with a new circuit board

[TehMarchant]

Ok I Just dug out the data I have on the 4inch O.E Smiths Tacho and the one in the picture is a O.E Most likely from a MGB.

 

The 4" RVI Rev Counter for positive earth vehicles came in 2 O.E styles

 

1. The (64-67yr)  RVI Positive Earth with a White Inductive Loop through a plastic clip on the rear which can be modified to work on a Negative Earth Car as per the after market Instructions above and also by opening the case and swapping the connections

 

The (68-72yr) RVI Positive Earth had no external White inductive loop and was designed with a inductive pickup inside and is not designed to read with the wires swapped around, they may show some indication of revs but can be +/- 2000rpm.

 

Not being rude when I say this but the rev counter in the OP picture needs a total refurb and no one would put it in there car surely even if it worked?

 

Mine I took out is immaculate compared to the one in the picture above but even RVCs are 40yrs old and read all over the place like mine when going through the gears (Bouncing needle ) stabilizes when constant revs, Speedy Cables can referb them but it £100ish with a new circuit board

Sheet thanks for that, I think by the description I have the 68-72 one. I love the look of this tacho, any idea if this board would be able to fix it? http://www.ebay.co.uk/itm/Smiths-RVI-to-RVC-Tachometer-conversion-board-includes-calibration-cable-/380578001095?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item589c3770c7  I was planning a refurb anyway

[spaulwill]

Depending on the circuit wiring backwards could permanently damage the gauge as its DC it is polarised. But if you do try it you do need to ensure there is no contact between the shell and car body, I think it's a bad idea better get the correct gauge for your car.

[KernowCooper]

Your number Tacho is not listed but email the guy and ask if it works 100% before you part with any money

[TehMarchant]

Okay thanks guys, I will email the Ebay seller, and I have also emailed speedycables to see about getting a RVC board put in and that will set me up for if i ever get electric ignition.

 

I really like the look of this gauge so I don't really want to get a different one if I can help it.

 

Thank you so much for the help from all of you! Top notch!