Modern Tach won't work with points?

[markdtn]

I have a Ford 8N tractor with an 8BA V8. It was in a 2N in my Avatar but I have since swapped it to an 8N over last Winter. the 2N did not have a place for a tach but the 8N had a "proofmeter" that was like a mechanical tach. Since I can't do that, I wanted a tach with an hourmeter that kind of looked like the proofmeter. So I bought one on Ebay that was a marine style. It was an open box, old shelf stock. I hooked it up and the hourmeter worked but the tach never went over 1000 rpm. Chalked it up to bad tach. Then I bought a cheap offshore tach on Amazon. Same thing, never over 1000 rpm so I sent it back. Finally, I bought a VDO marine tach. Brand new. I have verified the settings, 4 stroke, 8 cylinder, and correct pulses (it actually came out of the box set up like that). The instructions from VDO show hooking to a coil (- of course) but don't exactly address points type ignition. Just FYI I am running a stock Loadmatic distributor with some NOS 1990s Ford points and condenser. I am running 12V negative ground with an alternator. It has a 4-post Motorcraft starter solenoid so it gets 12V for starting to the coil and has a ballast resistor for normal running. The engine runs fine and has since 2017 with no changes to the distributor. Starts instantly when it's warm. Last I checked-but it's been a while-I was getting a reasonable value for RPM with an old Sears tach/dwellmeter.

Anybody else have trouble with modern tachs not reading with points? Any suggestions on what I should be checking? Thanks!

[Bob C]

Maybe go here and select your tach then go to downloads and it shows all the wiring and other info.
https://vdo-instruments.com/vdo_seri...ies=tachometer

[markdtn]

I have the instructions. It's a 3331106. It shows up on page 71 of this catalog. So it's older but was brand new in a sealed box.

https://www.vdomarinegauges.com/wp-c...-Catalog_1.pdf

If you hold a button down while turning the ignition on it toggles between programming modes. You can set it to 4 stroke and 8 cylinder in 1 menu and then set the pulses in a second menu (both of these were set correctly for me out of the box).

I'm just perplexed at why 3 different tachs all act the same and will not show over 1000 rpm? I'm going to dig out the Sears dwellmeter and make sure it still reads reasonable numbers for RPM. Just wondered if anybody else had seen this issue and what fixed it.

Thanks!

[big job]

could be you answered your question >modern tack< nobody know what points are but thats how they work simple hook up, wire ground , wire ign feed plus & one wire to the distributor side of coil worked for me. The holy grail to me is the Sun with its transmitter but take a loan to buy one & I do have those beauty's . for yours just 2500 rpms maybe correct for tractor duty. dont feel bad all I do is a problem. So proud I bought a sweet proofmeter & cable for my 8N dum me did-dent look at governor No drive and then ebay governors with tack all are around $350 I just looked at my dump truck V8 391 points and its called a football sun 3500 rpm they are on ebay same wiring . oh not a foot ball but has its shape just logo sam

[JayChicago]

Just a wild guess:
You are feeding through a ballast resistor, which limits current and drops the voltage. Maybe voltage is too low for these tachs? You could try by-passing the resistor one time to see if it makes a difference.

[markdtn]

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I played with it a little last night. Points are gapped at .015 which is between the .014-.016 that my Motor Manual calls for. The '80s Sears Tach/Dwellmeter I have does seem to read more accurately. It did show 1500 or so RPM at times revving it. I am getting 12V to the coil cranking and 6v (roughly, I was reading with the Tach/Dwellmeter not a multimeter) running. I flipped over to dwell from RPM and then it quit working. But all the timing stuff seems to be OK. I guess I need to reach out to VDO and see if they have any suggestions.

[markdtn]

Originally Posted by JayChicago

Just a wild guess:
You are feeding through a ballast resistor, which limits current and drops the voltage. Maybe voltage is too low for these tachs? You could try by-passing the resistor one time to see if it makes a difference.

Interesting! Maybe it has to have a 12V coil to function with these modern tachs. If so, I wasted a lot of time and effort on my wiring. I did several things to keep the ballast resistor and 4 pole starter solenoid-even though I have a mini starter (to avoid cutting the tractor bellhousing this time).

[tubman]

When we built our 6 to 12 volt tachometer converter box, we found we not only had to boost the tach logic (red wire) to 12 volts, but also had to raise the signal voltage (green wire) to 12 volts. (This is in addition to changing the polarity on both.) It would not work reading the 6 volt signal. That's part of what turned a seemingly simple project into a complicated one. You get varying results from different tachometers; some don't work at all, while others are inconsistent. If you keep looking, you may find one that works correctly, but that will probably involve a bunch of time and money.

Cleaning up the "dirty"power inherent to 6 volt systems was the other part of the complication of the project. You think you have it, and then pffft! your tach is toast.

[hueyhoolihan]

modern electronic devices are simple computers and so need to be powered. and the power requirements are very restrictive; not enough or too much and, IME, they may not work right or may not work at all.

[markdtn]

I have a Delco 10Si alternator hooked up as a 3-wire. So I am powering it with 12V to the tach. But the coil is 6V when running and 12V when starting using a 4-pole starter relay like many Fords with coils. I think if I am hearing correctly that I must use a 12V coil and get rid of the ballast resistor to make this work? If this is true, then modern tachs don't work on Fords or GM into the mid 1970s? (Pre Duraspark and HEI)

What is the latest and greatest on a good 12V coil? Bosch blue 00012?

[40cpe]

Maybe you just need to take the 12v power for the tach ahead of the ballast resistor. I don't think the signal wire on the distributor side of the coil matters.

[markdtn]

The only 6V thing that goes through the ballast resistor is the coil. Everything else is 12V (lights, voltmeter, tach, electric fans). I didn't think the coil negative side/tach signal would care about voltage but perhaps it does.

Here is a wiring diagram in case anyone is interested. It does not show the tach but it gets 12V ignition power from the junction block as a yellow wire, ground from the dash next to it (with a star washer), and signal from the - side of the coil.

[Jack E/NJ]

>>Maybe you just need to take the 12v power for the tach ahead of the ballast resistor. I don't think the signal wire on the distributor side of the coil matters.>>
> > I didn't think the negative side would care about voltage but perhaps it does.> >


Correct. Points 'open' should be 12volts with or without ballast. 'Closed' should be ground 0.

[hueyhoolihan]

for diagnostic purposes, you might be able to experiment using different batteries with different voltages to power the tach independently of the car's electrical system. i've got a few sets of small and large types of jumper cables that i've used to good effect over the years to diagnose electrical problems.

i also several batteries of various voltages. 6v, 8v, 9v, 12v, etc. that have been put to good use. just the other day i was installing a new cigarette lighter in my '41 and used my spare 9v multimeter battery to test it out, as i didn't have any wire under the dash at the time to plug it into. it got hot alright!

[tubman]

I think switching to a 12 volt coil (and changing the wiring accordingly) will work. There are 2 electrical feeds needed by the tach. The tach logic itself is designed to use 12 volts. But the signal coming from the distributor (green wire) has to be 12 volts as well. I have been there and done that. We at first thought that the voltage of the ignition signal "just had to be there", but soon found out that it also has to be the proper voltage and polarity.

[markdtn]

Originally Posted by tubman

I think switching to a 12 volt coil (and changing the wiring accordingly) will work. There are 2 electrical feeds needed by the tach. The tach logic itself is designed to use 12 volts. But the signal coming from the distributor (green wire) has to be 12 volts as well. I have been there and done that. We at first thought that the voltage of the ignition signal "just had to be there", but soon found out that it also has to be the proper voltage and polarity.

After reading your post I believe you are probably on the right track. All 3 tachs I have had acted the same way. I-and probably many of you-think of the mid '70s as not that long ago but it was 50 years. And my 1950 8BA was 75 years ago now. Lots of water has flowed under bridges since then. So maybe it's not so crazy that modern tachs won't work with pre-electronic ignition, ballasted 6V coils of the '70s and prior.

I am going to buy a 12V coil even if it messes up my beautiful wiring job.

So, best recommendation on a 12V coil still a Bosch blue 00012?

[tubman]

For you folks that doubt my credentials : https://www.youtube.com/watch?v=TaxpuDkWAqc.

[Don W/Norfolk]

Westach has an assortment of 6v & 12v tachs that work with points.
https://www.westach.com/tachometers

[markdtn]

Originally Posted by Don W/Norfolk

Westach has an assortment of 6v & 12v tachs that work with points.
https://www.westach.com/tachometers

Those do look nice. But not exactly what I need.

I am trying to create a "look". I want to as close as possible re-create the proofmeter. So in a perfect world it would be white face with black letters and a black needle with an analog hourmeter. It would have a black bezel, not chrome. That is a pretty easy gauge to find in a Stewart Warner mechanical type, but short of converting a Corvette tach drive distributor there is no way to get a mechanical tach signal on an 8BA that I know of.

The first electric one I got was a Teleflex. It had black face with white letters, white needle, chrome bezel, and analog hourmeter.

The VDO is black face with white letters, white needle, black bezel, and digital hourmeter.

So neither is "perfect" but either would have been "good enough". I think I try a 12V coil next. It is not too hard to convert my wiring to eliminate the ballast resistor.

[Bob C]

This is what you need to run your proofmeter.
Here's one on epay. https://www.ebay.com/itm/17643238310...PF1EHWD96BV82B