Factory Tach with Electronic Ignition

[am3rican]

I feel like I've researched this one to death but can't find answers to several questions.

I have a 68 Roadrunner that was converted to electronic ignition (with Orange box). When I received the car, the tach did not operate at all. It is pegged at '0'. I am guessing it is due to the electronic ignition. I would like to get the factory tach working again. I have not done any diagnosis other than checking voltage to the fuses in the fuse box. I am not sure where to start given my setup. All advice I have seen is based on a points ignition setup.

I have read that there is a device or switch I can purchase that will get the tach working again. Can someone tell me what it's called and where to source it? To those who have gone this route: is the tach accurate and does it bounce?

I have called Redline gauge works. They want $200 to convert it. Plus cost to ship the gauge there. Not sure If I want to spend that much until I explore all other options.

Also - All other gauges are in good working order. Only other complaint is that the dash light does not come on. Again, I have not diagnosed but I am convinced the previous owner tried to solve the issue as the dimmer wheel looks new, and I have a box of parts with dimmer switch / wheel with corroded connectors.

 

[am3rican]

Done some more research. I know for sure I have a Mopar performance electronic ignition. I've been told that this type of ignition system should not affect my Tachometer function.

I am now back to square one. I have ordered a multimeter and will be checking continuity and such.

 

[red 69 runner]

I put a factory tach in mine with electronic ignition and it works fine,maybe you just have a bad tach?

 

[71charger_fan]

The tach should take its signal from the neg side of he coil. It shouldn't matter if you're running points or electronic. I've got a factory tach and MP electronic ignition in my '71 and it works just fine.

 

[66Satellite_in_NC]

Should have 3 wires. 1 to fuseable link in fuse panel (+), 1 to ground (-) and last one to coil on the negative side. If you have a way of testing the tach on a friends car, go that route to verify that the tach actually works.

 

[Lazarus]

I'm glad you asked this question, because I have the same issue. When I bought my car, the tach worked, but after the rebuild we put in an electronic ignition and it stopped working when all put back together. The engine installer to,d me it was because of the electronic switch too. I also called redline and they offered to fix for big $ too. It sounds like it may just be wired wrong.

 

[am3rican]

The tach should take its signal from the neg side of he coil. It shouldn't matter if you're running points or electronic. I've got a factory tach and MP electronic ignition in my '71 and it works just fine.

I would have thought the same thing. But from what i've read, the Mopar Performance ignition should work fine. However, an MSD e-ignition will require an additional adapter.

 

[AMX364]

MSD demands its adapter or one like it, MSD only not HEI or regular electronic ignition. Check wiring to tach, most likely under hood.

 

[Lazarus]

Ok, I guess the water is a little muddier now than before, since some electronic ignitions do require a change and others don't. I hope to not hijack this thread, but anybody know if a petronix electronic ignition hooks straight up or requires something more. Thanks

 

[AMX364]

Lazarus--start a new thread so you can get the headline and maybe a answer. I do not know your answer, but someone does!

 

[kiwigtx]

A factory tach definitely works with a factory electronic ignition upgrade. Other brands of electronic ignition may demand the use of an intermediary tach adaptor unit.

Also I can tell you that the Rev-n-nator unit works perfect with the factory setup - true plug and play alternative to the Mopar ECU.

 

[am3rican]

Ordered a multimeter off Amazon. Only was $20 for a digital version. Will be testing sometime next week.

 

[moparmarks]

Most tachs work with the Chrysler factory electronic ignition. Sun, Autometer, VDO, ect.
Green Negative of coil
Red Ignition switch hot
Black Ground
Blue or yellow Dash lights.

 

[SwedCharger67]

It's a slightly tricky subject.

My 67 factory tach relies on the dirty voltage generated at the negative side of the coil. The factory tach needs to see the switching on/off voltage overshoots/overvoltage spikes to work correctly.
Any beautiful voltage curves will not work. Electronic boxes not having distinct switching characteristics, but more "rounded" curves may not work either, since those curve forms generate less voltage spikes, and the tach may not see it.

Also boxes with multi-spark will make the tach see a different type of curve, and that may not work either.

A pretty digital 0-12V output will not work either, since the factory tach needs the ugly wave forms to function properly.

My MegaSquirt system is outputting a pretty square wave for the tach, and the original factory tach will not work. I've bought an interface that will (hopefully) generate the dirty voltage spikes needed for the factory. I haven't tested it yet so don't know if/how the box works.
I believe it's this one that I bought for interfacing MegaSquirt to the factory tach:
http://www.summitracing.com/int/parts/msd-8920/media/instructions

I'm afraid a simple multimeter is not of much help in this case, only an oscilloscope can show exactly what's going on.

 

[am3rican]

It's a slightly tricky subject.

My 67 factory tach relies on the dirty voltage generated at the negative side of the coil. The factory tach needs to see the switching on/off voltage overshoots/overvoltage spikes to work correctly.
Any beautiful voltage curves will not work. Electronic boxes not having distinct switching characteristics, but more "rounded" curves may not work either, since those curve forms generate less voltage spikes, and the tach may not see it.

Also boxes with multi-spark will make the tach see a different type of curve, and that may not work either.

A pretty digital 0-12V output will not work either, since the factory tach needs the ugly wave forms to function properly.

My MegaSquirt system is outputting a pretty square wave for the tach, and the original factory tach will not work. I've bought an interface that will (hopefully) generate the dirty voltage spikes needed for the factory. I haven't tested it yet so don't know if/how the box works.
I believe it's this one that I bought for interfacing MegaSquirt to the factory tach:
http://www.summitracing.com/int/parts/msd-8920/media/instructions

I'm afraid a simple multimeter is not of much help in this case, only an oscilloscope can show exactly what's going on.

Thanks for the info. If the wiring checks out, I'll look into the oscilloscope. Can you tell me where I can get one

 

[SwedCharger67]

Thanks for the info. If the wiring checks out, I'll look into the oscilloscope. Can you tell me where I can get one

You could have a look at these ones:
http://www.picotech.com/oscilloscope.html
You should be ok with a very simple version.

I have a similar unit, but a German make.

 

[am3rican]

You could have a look at these ones:
http://www.picotech.com/oscilloscope.html
You should be ok with a very simple version.

I have a similar unit, but a German make.

Dang...$200 for the oscilloscope. I'm impressed with your dedication .