Tach Not Working

[thejobrien]

Been trying to tackle some of my gauge issues that have popped up recently - with most being solved now I'm shifting my attention to the tach. Ever since I got the car, the tach hasnt worked. The car is a 77, and the engine was swapped to a 79 3.0. The PO said ever since the 3.0 went in, the tach stopped worked. Have been doing some research on here and I've come to some conclusions (with the help of some of you on here) but I have some questions before I start on the wiring!

So from what I've seen on here, the 77 chassis harness and the SC engine hardness have some connection issues that might be plaguing the tach. Took a look at the 14 pin connector, and there is no pin connecting anything at the #12 pin where the SC engine harness has the black and purple wire going to. The 77 chassis harness upon further inspection has the black/purple wire coming out of the loom right by the CDI going to a 2 prong T connector (I understand the 77 and 2.7 read the tach right off the distributor?)

So my question is this..if my chassis tach wire is is going to this white connector and the engine harness/CDI black/purple wire is running between the 14pin and the CDI..do I need to splice in the chassis wire either into the 14 pin connector where the black/purple wire is? Or maybe at the white T connector? At the end of the day the CDI TD terminal needs to connect to the TD terminal on the tach..right?

If thats the case, what happens with the brown/red wire connected to the white T connector show in the picture? I have seen that it is the Air Flow sensor? If its plugged into the white T connector with the tach wire on the other side is the brown/red wire even functioning at the moment?

[timmy2]

Run purple/black to 2 pole T2 connector. Run brown/red to the single brown/black connector normally below the male 14 pin connector.
Purple/black and brown/red are in the 6 pin CDI wiring branch coming out by the 14 pin female connector, so fairly easy to get it out after removing the tape in between.
You can pull the brown/red out at the same time and run it over to the single plug.
Tape it back up, Done.

[thejobrien]

Originally Posted by timmy2

Run purple/black to 2 pole T2 connector. Run brown/red to the single brown/black connector normally below the male 14 pin connector.
Purple/black and brown/red are in the 6 pin CDI wiring branch coming out by the 14 pin female connector, so fairly easy to get it out after removing the tape in between.
You can pull the brown/red out at the same time and run it over to the single plug.
Tape it back up, Done.

Thanks Timmy, for the purple/black 2 pole are you saying just unplug the red/brown currently in the connector, remove the purple/black from the 14pin connector and unwind the tape then simply put a spade on it and connect where the red/brown wire currently is?

And for the red/brown wire hookup, is this the black/brown you're referring to right behind the relay?



-Jordan

[timmy2]

You got it.
It will all become clear once you remove the tape.

[thejobrien]

Originally Posted by timmy2

You got it.
It will all become clear once you remove the tape.

\

gotcha, thank you Timmy! Will give this a go this weekend

[PeteKz]

Thanks Timmy and thejobrien. I'm watching this thread so keep posting.

I have a 1973.5 car and a 1980 RoW CS engine. When I did the swap many years ago, I got some advice and got it wired up so that everything works reliably between the 1980 CDI box, the wiring harnesses, and the original tach.

Then a couple years ago, I had some alternator issues, so I used that as an opportunity to install a WOSP 175 amp alternator. Because it has an internal regulator, I subsequently removed the VR and the module that sits below it. So I now have some leftover connectors related to the voltage regulator and a couple other 1 or 2 pin connectors hanging out in the breeze, plus some wires/pins in the 14-pin connector that don't connect to anything. I'm thinking of cleaning up the wiring harness by removing the wires that went from the alternator to the regulator and other needed stuff, but I need to be careful not to "oversimplify" it and lose the alternator/battery light or some such.

Anyway, at some point I may start a thread on that project, but for now I'm watching this thread.

BTW, the module that sits just below the VR on the electrical panel--what does it do?

[timmy2]

Noise suppression

[thejobrien]

Originally Posted by PeteKz

Thanks Timmy and thejobrien. I'm watching this thread so keep posting.

I have a 1973.5 car and a 1980 RoW CS engine. When I did the swap many years ago, I got some advice and got it wired up so that everything works reliably between the 1980 CDI box, the wiring harnesses, and the original tach.

Then a couple years ago, I had some alternator issues, so I used that as an opportunity to install a WOSP 175 amp alternator. Because it has an internal regulator, I subsequently removed the VR and the module that sits below it. So I now have some leftover connectors related to the voltage regulator and a couple other 1 or 2 pin connectors hanging out in the breeze, plus some wires/pins in the 14-pin connector that don't connect to anything. I'm thinking of cleaning up the wiring harness by removing the wires that went from the alternator to the regulator and other needed stuff, but I need to be careful not to "oversimplify" it and lose the alternator/battery light or some such.

Anyway, at some point I may start a thread on that project, but for now I'm watching this thread.

BTW, the module that sits just below the VR on the electrical panel--what does it do?

Thats my idea too, not to oversimplify and if I do any corrections they need to be reversible haha. Hopefully, this is the last of any "major" (not really major, its just a tach to me..) electrical or wiring things but thats just me being hopeful haha.

As for the module under the VR, it seems to be the radio suppressor? A search on here shows that it is supposed to suppress radio frequencies from the ignition system so they dont get funneled into the car from the radio...I believe? Thats about as much as I know haha.

-Jordan

[thejobrien]

Does anyone know how to release this wire from inside the white T connector? It’s hung up on something and for the life of me I cannot find the tab to release it. I have it disconnected from each other, but I need to remove the brown and red wire from the white connector

-Jordan

[spuggy]

Originally Posted by thejobrien

Does anyone know how to release this wire from inside the white T connector? It’s hung up on something and for the life of me I cannot find the tab to release it

Never tried, but almost certainly it has a tang that springs out from the side of the terminal and holds it inside the plastic block.

If you can, it helps a lot to figure out exactly what terminal it is, and to look at one. Here, for example, is a TE/AMP "Junior Timer" female terminal - used on a lot of CIS connectors.




Sometimes, you can use a small pick (or jeweler's screwdriver) to release it from the back - but more often, these are intended to be released from the front, or mating side. Sometimes by a very thin pick, sometimes (round connectors) by a tube with an ID slightly larger than the terminal pushed over the terminal and into the mating side of the connector block. Sometimes the thing holding it in is part of the terminal block, but more usually it's on the connector itself.

Like these generic release tools:



The generics tend to be cheap/flimsy - and may or may not work well (or at all) with specific, proprietary, connector systems. But they might work well enough, once or twice...

The "real" tools are orders of magnitude more expensive, and don't fold up the first time you try to use them... I own a fairly wide selection of crimping and terminal release/de-pinning tools (Deutsch, AMP, Weather Pack, SuperSeal etc) - and I don't even work with wiring at all if I can help it.

If you're intending to re-make the connection, please do ensure that the terminal tang is pushed back out as far as it should be, locking the terminal into the connector block properly... Or you could spend considerable time chasing a connection that beeps out 100% for continuity on a DMM, but doesn't deliver a "real" signal "sometimes" - so your ECU, now and again, "sees" no crank reference, for example. Ask me how I know...

To use, all the ones I've seen are some variation of "push the wire end deeper into the plastic block so there's some play and release the tang from the other side". Something like this:

[timmy2]

Look at the white connector at the end that goes into the mating connector.
See how it looks like a T with a short leg?
Insert a small jewelers screwdriver in the short leg slot with the blade parallel to the longer slot.
Turn and twist to release the locking tab. Push and Pull on the wire and the terminal will release.
May take a few tries.
This is a link to what the terminal looks like so you can visualize the tab you are trying to depress.
Baomain Female Spade Quick Splice Crimp Terminals 6.3mm Crimp Connector Non Insulated Pack of 100 https://a.co/d/aDhrVIT

[thejobrien]

Thank you Timmy, Spuggs with the tips, did some searching around and found a pretty good generic took from O'Reillys that did the trick

https://www.oreillyauto.com/detail/c/lisle/lisle-wire-terminal-tool/lis0/56500/v/a/61/automotive-car-1977-porsche-911?q=lisle+terminal&pos=0

Once that came out, it was smooth sailing. Peeled back some tape, routed the purple and black wire from the 14pin connector to the white 2 prong T connector, rerouted the black/red wire from the T connector to the brown/black wire by the 14 pin and presto.....the tach was working! First time seeing it work in the car, and its nice to have it right there when banging through the gears. Is there supposed to be a slight tick from behind the dash, presumably where the tach is? (only happened once the tach started working) Other than that, it was a breeze.

Just want to say thank you to everyone with the help. Appreciate it.

-Jordan

[spuggy]

Originally Posted by thejobrien

the tach was working! First time seeing it work in the car, and its nice to have it right there when banging through the gears.

Woo-hoo! Noice!

Originally Posted by thejobrien

Is there supposed to be a slight tick from behind the dash, presumably where the tach is? (only happened once the tach started working)

LOL. The infamous click behind the dash that's driven many an owner crazy....

My car does it sometimes; I notice it most in cold weather with the heat/air going to try to keep the screen de-fogged. I think it's the instrument glass expanding/contracting..

On some cars, supposedly the O2 sensor box. I don't have one of those.

On some cars, supposedly the clock. I've don't have one..

On some cars (potentially including yours), it could be the OXS counter located behind the speedo in the dash. It's driven off terminal A on the speedo (also used as cruise control input); you know the OXS light on the top of the dash that lights up when you turn the key to On? The counter will turn it on solid every 30,000 miles, until you press the reset button on the counter box itself. It's an indication that the smog equipment (smog pump/catalytic convertor/O2 sensor) should be inspected/serviced.

If you don't have that smog equipment or cruise control, you can just disconnect it and it won't make a sound ever again. Multiple ways to do it; I'd just pull the piggyback and the power feed from terminal A.

OXS Counter
Solved: OXS related ticking sound from the dashboard of 911 SC

[timmy2]

Good job.