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JH TACHOMETER VS PERTRONIX IGNITION  Rating:  Rating
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 Posted: 08-08-2010 05:30 pm
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timeforwalkies
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Anybody had this problem?
I have the Pertronix ignition system installed and the car runs great.  But now the tachometer show zero rpms.  Even went to the trouble of installing a second one that I knew worked from my donor car.  Still zero.
So what the heck is wrong here?
Thanks
Clif
Found it and it looks like mine.  Didn't remember what the answer was and couldn't find it through search.
If anybody has more to add that would be great.  Sometimes new solution come up.

Last edited on 08-09-2010 05:50 am by timeforwalkies

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 Posted: 08-08-2010 07:21 pm
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Art DeKneef
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Search the board here. I believe this has been discussed here a couple of times before.

From my fuzzy memory on this it has something to do with the tach needing to be rebuilt or swapped for a different type due to the different electronics of the Pertronix. Or it has something to do with the ballast resistor.

If I remember correctly this is something I think Pertronox is aware of and calling them may help resolve the issue.

I'm sure someone else will have the correct reason and will pipe in.

Art

 

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 Posted: 08-10-2010 05:31 am
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timeforwalkies
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OK.  So I finally figured out what to do via the Pertronix website, but not how to do it.
They say "...relocate the tachometer trigger wire to the white wire from the Second Strike box".
Very clear if you know which wire on the tachometer is the trigger wire, that is where that wire is located under the hood.
Anybody know which one is which?
Thanks,
Clif

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 Posted: 08-10-2010 02:56 pm
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Jensen Healey
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It's a white wire (on some cars white/ slate) connected to the ballast resistor on the firewall.

Kurt

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 Posted: 08-10-2010 04:56 pm
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timeforwalkies
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Thanks Kurt.
However, I don't see anything on the firewall that has a wire connected to it.  Several wire flitting around the coil.  I hear there may be a difference on 74 1/2 cars, but still that doesn't help if you don't know what the difference is.
Thanks again,
Clif

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 Posted: 08-10-2010 11:00 pm
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Gary Martin JH 15371
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OK, the Pertronix has two wires, a red and a black. The wire coming from the tach (usually the white/slate wire) is the same wire that provides power to the ballast resistor next to the coil, or if your car does not have the ballast the wire will go directly to the + or positive side of the coil. If your car has the ballast, the white/slate wire will connect to one side of the ballast, the other side of the ballast goes to the +/positive side of the coil. The tach wire is also the ignition wire from the key. Some cars use two wires for Ign and Tach, but the JH it is just one wire.

Hook the red wire from the Pertronix to the same location on the ballast resistor that the white/slate wire from tach/ign connects to. If no ballast, then connect to the + positive side of the coil. The black wire from Pertronix connects to - negative side of the coil.

This is how my 74 is hooked up (I have the ballast resistor). Tach works on my car, but it jumps around at times. Most of the time it reads correctly.

Gary  

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 Posted: 08-11-2010 01:37 am
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timeforwalkies
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Thanks Gary.
Just one thing, well maybe two.
The Second Strike Pertronix has six wires.  Black, Red, Yellow, White, Orange, and Green.
Their diagram shows:
Black to battery negative.
Red to battery positive.
Yellow is not used.
White to tach output.
Orange to original tach wire
Green to original ignition switch wire

At present the white wire is not hooked up.
Pertronix:  http://www.pertronix.com/support/manuals/pdf/second_strike%20.pdf
Pertronix says "...relocate the tachometer trigger wire to the white wire from the Second Strike box"

Do you have the second strike unit, Pertronix 500?

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 Posted: 08-11-2010 06:17 pm
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Gary Martin JH 15371
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My Pertronix only has two wires. I don't have the second strike unit. I think you need to find someone that has installed the second strike unit on a JH. On a JH the ingition wire goes through the tach and on to the ballast resistor. There is no separate tach signal wire. Sorry I'm not more help.

Gary

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 Posted: 08-11-2010 07:45 pm
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Greg Fletcher
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There was an interesting tidbit in the newsletter a while ago-

The cure is simple- you need to procure (2) 400V 3A diodes and place them in series (with the bands pointing in the correct direction). The diodes are fairly common and can be found at most electronic stores, or at Radio Slack stores under part# 276-1144.

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 Posted: 08-11-2010 08:06 pm
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timeforwalkies
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Thanks Greg.
Place them in series where?
Clif

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 Posted: 08-17-2010 01:49 am
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jdenglish
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Several years ago there was a shop in North Hollywood that would convert  tachometers.  It was featured in an article in the JHPS mag.  I currently use a Pertronix and MSD unit to the converted tach.  A long way around the problem but it works.

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 Posted: 08-17-2010 02:49 am
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Jensen Healey
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I use a 3 1/8" VDO tach that plugs in to the MSD. Accurate tach? What a concept!

Kurt

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 Posted: 09-09-2015 03:22 am
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wtberks
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Greg, I installed the Pertronix distributor and would like to get my tachometer working. So, this information regarding diodes, could you elaborate. For example, where do I place them?

Thanks,
Bill

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 Posted: 09-09-2015 01:57 pm
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NigelK
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Hi Bill

The fundamental issue here is that the original Jensen-Healey Smiths tachometer is designed to be wired in series with the coil ("current triggered" or "RVI"). Compared to points, electronic ignition systems do not always generate sufficient current to trigger this style of tachometer.

I say "not always", because current triggered tachometers are reported to work with some electronic ignition systems, but not all. For example, when I switched my GT from points to Accuspark electronic ignition, the tachometer continued to work (albeit not very accurately). But when I changed to Lucas Constant Energy ignition, the tachometer stopped working.

More modern tachometers are designed to be wired in parallel with the coil ("voltage triggered" or RVC) and will always work with electronic ignition systems.

So while there may be several ways of getting your RVI tachometer to work with the Pertronix, the only guaranteed fix is to convert your tachometer to voltage triggered operation (Google "RVI to RVC conversion") and switch a couple of wires between the tachometer and the coil so they are wired in parallel. This is not as big a job as it sounds.

I used Spiyda Design in the UK to convert my original RVI tachometer to RVC operation, LotusBits fitted it and changed the wiring, and the tachometer now works fine while looking stock.

Hope this helps.

Best wishes,
Nigel

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 Posted: 09-09-2015 05:21 pm
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wtberks
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Thanks Nigel. Yes, the information does help. I am in Southern California and a bit of research has led me to North Hollywood Speedometer http://www.nhspeedometer.com. I am going to call them today to determine if it is worth the drive. I am trying to get a number of small items, such as my non working tach, fixed before I take my GT to the 2015 Jensen Western Region.

Bill
GT 30450

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 Posted: 10-06-2015 01:53 am
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wtberks
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I just installed my tach after modifying it using the board that I bought from Spiyda http://www.spiyda.com. Installing the board was really easy and wiring it back into the car was fast and simple. This was a fraction of the cost of having it modified locally.

The part that I purchased was Smiths Tachometer RVI to RVC conversion board #SP-RVI-RVC.

There are four videos showing how to take it apart, swap in the new board, power it up and calibrate it once done.

https://www.youtube.com/watch?v=ME_KKCpyJqE
https://www.youtube.com/watch?v=syQltmmU2W0
https://www.youtube.com/watch?v=Xeh_WB688VM
https://www.youtube.com/watch?v=dthIQ-1Cyuo

Last edited on 10-06-2015 11:13 pm by wtberks

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 Posted: 10-12-2016 07:43 pm
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Rick in Miami
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I am running my stock RVI JH tach with a Pertronix II. I still power my coil + terminal from the circuit that passes through the tach (including the pink/white resistor wire). I ran a separate 12v (white) circuit from my ignition switch to power the Pertronix. The tach works fine.

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 Posted: 10-13-2016 02:56 am
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Jensen Healey
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Rick, that is brilliant!

I haven't gotten around to installing my Spiyda Buffer due to other projects and obligations but hope to post a full report soon.

Kurt
JH 13148 and 19753

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 Posted: 04-15-2017 09:11 pm
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Rich W
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Rick,

Thanks so much! I've been driving without a tach (a couple years) since I installed the Pertronix II. What an easy fix!

Thanks again!

Rich

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