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Making the Tachometer work W/ a distributorless ignition system  Rating:  Rating
 Posted: 08-22-2007 01:12 pm
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Rob Rawe

Joined: 08-17-2007
Posts: 19
The '73 J.H.-vin#14120 I have has had a HPV-1 distributorless ignition by Electromotive,Inc. installed in it since June '98.  But the tach has not worked since then.

So recently I have been trying to tie up somethings left unfinished, after ten years of on going restoration projects.  So I contacted Electromotive, Inc. again to see what could be done to get the tach. to work, & they told me they had just started marketing a Tach. amplifier, so altought it was rather expesive I purchased one since they assured me that was what was needed to make the tach work again.

When it arrived their was not any wiring diagram w/ it, just  the color of the (4) wires noted on the Manufacturers label as follows;  white = Input,  black = Ground, green = Output,  pink = +12v.   So after several phone calls to their Technical support staff, & e-mailing a scanned copy of the J. H. wiring diagram, it was decided that the J.H. has a Current Triggered Tach. since the wire from the Tach went to the (+) side of the old coil & they told me it should be wired as follows; white = input to HPV-1 terminal marked tach.,  black = ground to body metal,  green = output to tach. "NOT TO BE USED" cap off so wire will not ground to any metal,  pink = to be connected to the (+) coil wire from the old tach.   I told the technition when I had a mechanic install the HPV sys. he had also used the (+) coil wire for the wire coming from the ignition switch to the high current relay per the HPV wiring diagram, & questioned if that would create a problem since their installation manual stated not to attach anything else to the HPV power supply circuit. He assured me it would work that way to make the tach function.

So last weekend I worked on getting the Tach. Amp. & wiring set up with the HPV, but when I turned on the key the engine started, but no RPM's registered on the tach. .   So after another call to the tech. rep. he told me it should have worked & if it did not I needed to install a new Tachometer since I had some kind of oddball tach. that was not reading the signal from the amplifier.

I told him a clubber had told me on the Message board, many moons ago, he had sent them his tach. & thay had modified it for him so it worked. So then he tells me to send in my tach. along w/ the new tach. amp. & they will look at the tach. to see if it can be modified & what the extra $ would be.

So I am hoping to find a club member that has Electomotive HPV sys. & managed to get the stock tach to work that can pass on some info. about the wiring. I still question the way I was told to set it up, but I don't know enough about automotive wiring to go any further.


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 Posted: 08-22-2007 02:49 pm
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Judson Manning

Joined: 03-14-2005
Location: Atlanta, Georgia USA
Posts: 406

Such are the challenges in adapting 40 y/o instruments to work with modern technology.  What you are describing is the same phenomenon with MSD ignitions.  Check elsewhere for that thread.

The JH tach is an analog device designed to measure the amount of current going through the coil (i.e. higher RPMs = more current).  Along with catalytic converts, and big bumpers, GM introduced their HEI system in 1975 forever changing tachs from analog to digital triggering.  I doubt the tech guys on the phone were even alive when analog was king.

The short answer is that there are adapter devices such as the MSD 8920 that will make the tach register by emulating this analog signal.  In my experience, the 8920 + Smiths Tach combination was not an accurate one.

In the MSD thread there is mention of a company in CA that will retrofit the Smiths tach to a modern triggering mechanism (ala Autometer, VDO, etc.) which will allow you to retain the stock look and achieve better accuracy.

After all my experimentation and frustration, I found it easier to install an aftermarket tach and focus on other areas of the car.


Last edited on 08-22-2007 02:53 pm by Judson Manning

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 Posted: 10-01-2007 04:00 am
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Joined: 04-15-2005
Location: Moorestown, New Jersey USA
Posts: 198

I also have an HPV-1 ignition system, and swear by it !

When I installed it, I had my tach modified to work in the digital world.  If you still have this problem, I can dig through my files to try and find where I had the work done.  Let me know.

Pete Bahr


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