Connecting correct wires for HEI ignition sys. - Pontiac GTO Forum
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post #1 of 10 (permalink) Old 11-15-2017, 09:19 AM Thread Starter
 
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Connecting correct wires for HEI ignition sys.

OK moving on to the HEI distributor ignition system. I have a factory hood tach and also a HEI distributor. Over the past two year while working on this 1967 GTO I have been let to believe that I needed special wires to connect the tach to the power supply to the HEI distributor. So I have purchased all of what I believe to be the correct wiring for this system. Now the new tach I purchased came with a tach wiring harness (see pictures of the harness and the two special wires I purchased from Ame's). My question is how to they all connect. Now I know that the distributor has the Batt and the Tach terminals and I am aware that I can attach the ends of the two wires to these terminals. My question is how or where do I connect the other ends of these wires.

Picture one is the ends of the new tach harness wires
Two is the HEI tach wire and the I turned the package over to show the two electrical ends. One will plug into the tach where does the other end go and should there be a plastic connector end?
Three is the HEI power feed wire and the flip of the package reveals the wiring ends. again the end with the plastic connector goes to the dist. but where and how does the other end connect.
Four is just the dist turned on its side so you can see the tach and batt connectors.

So some how I have to connect the tach harness wires to Hei tach wire and to the hei power feed wire. Some sort of diagram or a hand drawn diagram would be great.

There must be some one who knows the answer to this. Someone must have a hood tach with an HEI distributor who could look at their car and give me the answer.

thank you very much
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post #2 of 10 (permalink) Old 11-15-2017, 06:56 PM
 
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I thought you already asked this question and I answered it. https://www.gtoforum.com/f12/hood-tac...ibutor-123522/

Are you asking something different??
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post #3 of 10 (permalink) Old 11-15-2017, 08:30 PM Thread Starter
 
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Yes I do not have directions on how to hook up the hood tach. Nadda none. Also I am asking if you can just hook the tach directly to the HEI dist.. Wondering if the current from the HEI, which I believe would be higher than the original coil, cause any damage to the tach. At 250.00 per tach I can't afford too many of them. Also I was asking how the wiring pieces that I purchased would connect to the original hood tach plug, for lack of a better word.

I just feel that I bought wires that I will not need for one and second I don't want to toast my tach either.

thanks for you help

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post #4 of 10 (permalink) Old 11-15-2017, 08:54 PM
 
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Understand your frustration, but you might not find your answer here if no one has done what you are looking to do. If you purchased the hood tach from a reputable Pontiac parts seller like Ames, Year One, or OPGI, you can most likely email them and they will get you hooked up with the correct wiring sequence.

Second option would be to purchase an inexpensive tach. Summit has a couple for $31 - $34. Hook up the cheap tach to get all your wiring working and make sure it does work, then hook up your hood tach. If the tach fries, it's only $30 and you will have to come up with another solution.

Third option is to ditch the HEI, get an electronic distributor that uses a coil and hook it up as you normally would. It will also look stock with the coil.
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post #5 of 10 (permalink) Old 01-02-2019, 04:16 PM
 
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Originally Posted by PontiacJim View Post
Third option is to ditch the HEI, get an electronic distributor that uses a coil and hook it up as you normally would. It will also look stock with the coil.
For my '65, I purchased an original-type, in-dash tach (will be mounted in the blank/clock space) from The Parts Place, which I have not installed yet but would like to. I do have my electronic ignition (not HEI) from Summit installed. My ignition has the separate coil and normal diameter distributor, just electronic instead of points (Summit SUM-850400-1). From what you are saying above, it sounds like I can connect the "original equipment" tach, the same way I would if I didn't have electronic ignition, and things should be ok. Is that what you are saying or am I misunderstanding. I've been getting mixed opinions on this, just wondering if anyone has done this and whether there were any issues.

Thanks.
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post #6 of 10 (permalink) Old 01-03-2019, 08:07 PM
 
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Originally Posted by Pacos65&67 View Post
For my '65, I purchased an original-type, in-dash tach (will be mounted in the blank/clock space) from The Parts Place, which I have not installed yet but would like to. I do have my electronic ignition (not HEI) from Summit installed. My ignition has the separate coil and normal diameter distributor, just electronic instead of points (Summit SUM-850400-1). From what you are saying above, it sounds like I can connect the "original equipment" tach, the same way I would if I didn't have electronic ignition, and things should be ok. Is that what you are saying or am I misunderstanding. I've been getting mixed opinions on this, just wondering if anyone has done this and whether there were any issues.

Thanks.
Yes, it should connect right up like any tach with a points type distributor. I did the Pertronix I electronic conversion to my '68 points distributor and hooked up the aftermarket add-on tach to the coil with no issues. I used 12 volts going to the coil versus the 7-8 volts used with the resistor wire.

The factory wiring diagrams seem to show a 1 AMP inline fuse used on the wire going to the coil. I personally have never seen one, but the cars I owned "way back" were beat and good possibility that were long removed. So it may not hurt to protect your tach with the inline fuse.

In doing some more research, it seems to be a mixed bag as to what to expect from the tach with electronic conversion. Most say no problems, others do have accuracy problems. It could be that if you switch to a direct 12volt power source to the coil instead of using the factory resistor wire, you could have too much voltage going through the factory wire coming off your tach and make it act up. You may need to add a resistor to the tachometer lead (not the 12volts going to the coil if you are using 12volts), but being an aftermarket tach, you may be OK.

Just to give you an idea of what may need to be done, this is what Pertronix suggests if your tach gives you problems. You might use it for reference with regards to your set-up. A ballast resistor might also do the job and these are sold at Summit as well. http://support.pertronix.com/file.ph...50ad853083634b

If still uncomfortable, I would email Summit as well as the in-dash tach suppler and confirm what it is you are using and they should be able to give you a definite answer.

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post #7 of 10 (permalink) Old 01-03-2019, 10:04 PM
 
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Thanks for the response. Technical support at both Summit and The Parts Place wasn't real useful, neither wanted to commit with an answer.

From what I understand, the voltage spikes out of the primary will not be any worse with electronic ignition than the points, so I shouldn't damage the tach by trying it out. So that will be my plan - try it and see. Thanks.
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post #8 of 10 (permalink) Old 01-04-2019, 07:56 PM
 
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Originally Posted by Pacos65&67 View Post
Thanks for the response. Technical support at both Summit and The Parts Place wasn't real useful, neither wanted to commit with an answer.

From what I understand, the voltage spikes out of the primary will not be any worse with electronic ignition than the points, so I shouldn't damage the tach by trying it out. So that will be my plan - try it and see. Thanks.

Isn't it great when you have companies out here selling and promoting products to make the sale, then when you hit them up with the nitty-gritty tech questions they can't really pin down an answer or what you should try - and they seem to mumble at that point.

Like you, the tach is a 12volt tach so I can't see it being burned up, but the reading could be off if the tach volts required did not match the coil volt output. So I would give it a try myself and if it got weird on its readings, then I'd be looking to add a ballast resistor of some sort on the tach wire.
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post #9 of 10 (permalink) Old 08-18-2019, 05:22 PM
 
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just to close the loop, I installed the factory-looking tach in the clock space of the '65 dash. It works fine with my electronic ignition. I consulted with a very knowledgeable person before installing it, and he said the issue would be an intermediate voltage causing the problem if there would be a problem. Electronic ignitions don't just switch between open and closed, they also have current limiting, which means the tach will see some voltages between just the high and low. If the tach was not designed to accommodate this, it could have accuracy problems. I assume this tach was designed with that in mind, it seems accurate throughout the rpm range.
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post #10 of 10 (permalink) Old 09-07-2019, 09:19 PM
 
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The factory tachometer for a points type distributor will not be accurate with a HEI distributor. I had my 65 tach converted with VDO components at https://www.nhspeedometer.com/. They are very knowledgeable and can answer all your questions. So even a new tach if designed for a points type distributor will not work accurately.
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