OER, Pertronix lll and M&H - Chevelle Tech
Electrical & Wiring Troubleshooting electrical problems.

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post #1 of 62 (permalink) Old Oct 7th, 18, 11:52 AM Thread Starter
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OER, Pertronix lll and M&H

I know there have been a lot of discussions about Pertronix ignitions failing or having erratic Tach movement. I have a 68 Chevelle L79 and I changed to all new M&H wiring (highly recommend) and had them remove the resister wire and run a 12 volt lead with stock connections. I also installed a Pertronix lll Igniter with Flamethrower lll coil and a replacement OER roller tachometer. The OER was dead at first fire, dead meaning sitting at 1000 RPM with no movement so I contacted M&H because schematics for gauges are not in the assembly manual. I checked the brown wire from the coil to the gauge with an ohm meter, 12 volts (pink wire) to the gauge and ground from the gauge to chassis ground and all were good. I called Pertronix and they said I may have to add a resister or capacitor in line on the point lead wire but that wouldn't kill the tach and usually is erratic or inaccurate on some cars. After contacting OER they said to perform the checks that I already had performed but also mentioned a filter is needed with ANY high output ignition system. Personally I think I just received a DOA tach but I am looking for other members input running my configuration. I believe OER's statement stating any HEI type ignition will kill or burn up their tach maybe a stretch and I will hate to cut and splice my new harnesses for a maybe fix!. I ran igniter l and ll on my 69 Camaro SS and Buick GS and had no issues but these were factory tachs. I do have my factory tach that I can send out for a reface and repair but for now Jegs has gracefully replaced the The OER Tach and it is in route. So my question is what or who can I believe. Please refer only to my current configuration for replies. Thanks
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post #2 of 62 (permalink) Old Oct 7th, 18, 1:15 PM
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Refer to your current configuration with the exact same harness, Pertronix III and specific OER tach? Good luck!

I installed Pertronix III with the same coil as yours about 4K miles ago and a Bosh tach.

No issues, no filter cr**p required, tach is dead on.

So, don’t believe OER.
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post #3 of 62 (permalink) Old Oct 7th, 18, 2:43 PM
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Re: OER, Pertronix lll and M&H

I have a 67 with the same Pertronix III and coil as you with the original tach. The tach works just as it did before. I still have original wiring so I ran a 12 volt wire to coil. I would think your tach is bad.
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post #4 of 62 (permalink) Old Oct 8th, 18, 4:27 AM
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Re: OER, Pertronix lll and M&H

You cannot compare how different brand tachs work. Because a Bosch tach works with Pert does not mean that all other tachs will work with Pert.

You may indeed need a filter. Some tachs require a filter with HEI, some don't..
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post #5 of 62 (permalink) Old Oct 9th, 18, 3:24 PM
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Re: OER, Pertronix lll and M&H

The OEM tach will work fine on an HEI as long as certain circuit components are in good shape. The tach circuit has a zener diode with resistor and inductor to form a simple voltage regulator and filter circuit to manage the tach signal voltage input. Using an HEI instead of points will put a *little* more stress on that circuit (namely the zener) but should be ok, unless age has taken its toll. HEI dwell is a little different than points but will not make a significant error in tach accuracy.

The OER tach, which *may* have an almost exact duplicate of one of 2 GM circuits, could also have a very similar filter circuit. I have seen many repro tachs that will use the GM circuit (with a minor component value change), it is very common. But, it should also be fine with an HEI.

The Pertronix may or may not ouput a tach signal that is similar to points or HEI so can't speak to how accurate an OER or OEM tach will react

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post #6 of 62 (permalink) Old Oct 13th, 18, 8:02 AM Thread Starter
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Re: OER, Pertronix lll and M&H

Thank you for responses. I did change the OER roller tach with a new one and it still doesn't work. My old dwell/point/tach tester works fine when connected directly to the coil. I did verify that my wiring is correct from the coil to tach, 12V to tach and ground of the tach case to chassis ground is good. I have seen many complaints about erratic tach readings but I get absolutely no action regardless of RPM. I am at a loss. I would expect someone would have had a issue using a Pertronix lll and no tach function. Could a resister or capacitor correct this? Thanks again.
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post #7 of 62 (permalink) Old Oct 14th, 18, 3:17 AM
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Re: OER, Pertronix lll and M&H

You need a filter, as I mentioned in post #4. I believe a circuit diagram of one was posted on this forum just recently.

I have seen more than one type of filter design; the filter I use has more components [ seven ] than the one above.
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post #8 of 62 (permalink) Old Oct 14th, 18, 7:00 PM
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Wink Re: OER, Pertronix lll and M&H

Quote:
Originally Posted by Billdini View Post
I did verify that my wiring is correct from the coil to tach
Is the brown (signal) wire from the tach attached to the - side of the coil? Does your dwell meter work when attached to the tach wire at the tach in the dash?
Try running a wire from the - coil terminal to the tach, bypassing the factory wiring. If the tach works with this set up, then you have an open in the wiring, probably in the bulkhead connector.
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post #9 of 62 (permalink) Old Oct 15th, 18, 4:30 AM
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Re: OER, Pertronix lll and M&H

Well if OER said you need a filter, as the supplier they might just know what they are talking about....
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post #10 of 62 (permalink) Old Oct 15th, 18, 10:52 AM Thread Starter
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Re: OER, Pertronix lll and M&H

Hi, I did verify with a ohm meter that I had 12V at the tach and that I had continuity from the negative brown coil wire to the tach as well. My harness is all brand new but I called M&H to see how it was wired double checking how the wires run. Because this car has ac pulling the dash is a real PITA and i regret that I didn't run the new tach directly off the coil, battery and ground before installing. I did verify with my meter that the first new OER tach had resistance that varied for some reason between the coil and power input on the back of the tach where the new one and my old original tach is wide open which I can only assume is correct. I'm gonna try and see if my original tach that came with the car works wiring it directly although its pretty tough looking being exposed with a bad convertible top for years. I bought this car not running needing quite a bit of work so there are a lot of new parts.

Responding to Gtogeoff's comment, I agree they should know but they didn't say it wouldn't work at all but that it will be burned up. OER's statement was very broad in respect to all electronic ignition systems and since they didn't even know what type of ignition I was using even though I told them in my email made me question their response. However, I need to figure out how to best install this filter minimizing hacking my new harnesses just to be on the safe side. Pertronix does say some tachs need a resister and or a capacitor. I was just hoping for a definitive answer from one of the companies and besides M&H none really have. Thanks for all your comments.
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post #11 of 62 (permalink) Old Oct 16th, 18, 4:37 AM
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Re: OER, Pertronix lll and M&H

The filter can go under the dash, out of sight. I made my filter from components that I bought from an electronics store. I fitted them inside an old medicinal plastic pill bottle & brought out the three wires. I then pumped the bottle full of neutral cure silicon to lock it solid.
The bottle is tie-wrapped to the harness under the dash.
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post #12 of 62 (permalink) Old Oct 16th, 18, 12:09 PM Thread Starter
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Re: OER, Pertronix lll and M&H

Gtogeoff, I went off to U Do it up here and purchased all the components that Pertronix says I may need. Basically they say install a 10k 1/2 watt resister and if that doesn't do it then try 15k and 20k. If all those don't work then install a .01 1000v mf capacitor. None worked but I did discover something interesting though. if I turn on my running lights and with any resister in line the tach will go to 500 rpm and sit there regardless of engine rpm but that's a start. I also have another issue with a intermittent buzzing regulator so I checked my voltage at the battery with my Fluke as follows. Engine off=12.6v, engine idling 14.4v but then it will buzz and shoot up into the 16.5v range for a few second and come back down. As mentioned earlier I have replaced almost everything through this restoration although the term resurrection might be more fitting. The M&H harness looks and to date has tested perfectly. During the restore i changed the tach, gauge cluster, entire stem to stern wiring harnesses, horn relay, voltage regulator and the alternator. I know never change that many things at a time but in my case I had no choice.. I used my dvm checking resistance from the gauge cluster to chassis, chassis to frame, frame to motor and the radiator support. All came in good... Its acting like a ground issue but I installed all new grounds cleaning the surface completely. I should mention I am only using the two engine compartment harnesses and the main cluster harness connected to everything minus the intermediate harness, AC harness and steering column harness. To make things worse I do have a decent understanding of electronics being in computers throughout the years. I will stay on it but its making me crazy

Last edited by Billdini; Oct 16th, 18 at 12:25 PM.
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post #13 of 62 (permalink) Old Oct 16th, 18, 3:17 PM
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Re: OER, Pertronix lll and M&H

Quote:
Originally Posted by Billdini View Post
Gtogeoff, I went off to U Do it up here and purchased all the components that Pertronix says I may need. Basically they say install a 10k 1/2 watt resister and if that doesn't do it then try 15k and 20k. If all those don't work then install a .01 1000v mf capacitor. None worked but I did discover something interesting though. if I turn on my running lights and with any resister in line the tach will go to 500 rpm and sit there regardless of engine rpm but that's a start. I also have another issue with a intermittent buzzing regulator so I checked my voltage at the battery with my Fluke as follows. Engine off=12.6v, engine idling 14.4v but then it will buzz and shoot up into the 16.5v range for a few second and come back down. As mentioned earlier I have replaced almost everything through this restoration although the term resurrection might be more fitting. The M&H harness looks and to date has tested perfectly. During the restore i changed the tach, gauge cluster, entire stem to stern wiring harnesses, horn relay, voltage regulator and the alternator. I know never change that many things at a time but in my case I had no choice.. I used my dvm checking resistance from the gauge cluster to chassis, chassis to frame, frame to motor and the radiator support. All came in good... Its acting like a ground issue but I installed all new grounds cleaning the surface completely. I should mention I am only using the two engine compartment harnesses and the main cluster harness connected to everything minus the intermediate harness, AC harness and steering column harness. To make things worse I do have a decent understanding of electronics being in computers throughout the years. I will stay on it but its making me crazy
Do you have acess to an oscilloscope? It would be helpful to determine the tach signal waveform to find out if it is compatible with the tach circuit. You can get the cheap little add on board that turns a lap top or tablet into a oscilloscope. You wont need very much bandwidth, under 500 hz

Sent from my SM-T817V using Tapatalk
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post #14 of 62 (permalink) Old Oct 16th, 18, 3:32 PM
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Re: OER, Pertronix lll and M&H

FWIW,I race with a few guys (myself included) that run the former Crane now FAST XRi ignition module in our points style distributors and never had a problem with the factory tachometers working.
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post #15 of 62 (permalink) Old Oct 16th, 18, 4:11 PM
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Re: OER, Pertronix lll and M&H

I had a similar situation with my Autogage tach...it worked fine with the HEI and Pertronix setups....went to the MSD Pro Billet and 6530 programmable box...tach wouldn't work. They supplied a chart telling which ones would work and which ones required their tach adapter....of course mine required the adapter. Works fine now.....
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