Problem with adding tach/shiftlight to tach wire...

[Ramius83]

Ok, here is the dilemna. I installed a Harlan-shift light on my RB26 when I installed it. I tapped into the tach wire near the ECU. Ran an 18/22 gauge wire to the Harlan shift light. The harlan shift ligth works great.

However, now I have a bouncing tach. My main tach in the cluster bounces, struggling to show RPMs. And, it REALLY bounces and doesn't even move if I turn on the lights, apply the turn signal, turn on the defroster, etc.

Is there any way or any thing that can be used to "boost" the tach wire so I can add a shift light or aftermarket tach without this problem occuring. I thought I remember seeing something about this in the past, but I couldn't remember what it was. Thanks guys.

[Slo_240sx]

Its bouncing because of a bad connection. When you pulled on the wire you probably pulled the pin out al little bit of the ECU. When you tapped the wire did you solder it in? Do it and tape it/shrink wrap it.-Alex

[Ramius83]

Its bouncing because of a bad connection. When you pulled on the wire you probably pulled the pin out al little bit of the ECU. When you tapped the wire did you solder it in? Do it and tape it/shrink wrap it.-Alex

Thanks for the reply.

But, I didn't pull the pin out of the ECU a little. It is still intact.

I tried 2 different ways to tap into the tach line. First, I removed some of the sheething to the tach wire and solderless connected the shiftlight to the tach wire. That produced the formentioned results.

I then tried a second approach by soldering it to the tach wire. That produced the same results as well. But, the second I remove the shiftlight from the tach wire, the tach on the instrument cluster will work just fine. It only does this when the shiftlight is attached to the tach wire.

[FAST-DATSUN]

Most tacks require a MSD/Autometer converter box to work correctly on a DIS system.....

[Joe]

Most tacks require a MSD/Autometer converter box to work correctly on a DIS system.....

ill back this up

the tach has no idea whats going on because its a distributorless ignition system (DIS)

[Ramius83]

The problem is NOT that the tach/shiftlight isn't working.

I am not using an aftermarket tach or anything like that. I am just using an aftermarket shiftlight. I am using the stock S14 tachometer.

When I am using the shiftlight (ie hooked up directly to the tach wire), I have a bouncing tach. The shiftlight works perfectly fine, it just causes my tach to constantly bounce....

Can this be solved by that MSD/Autometer converter box?

[stiergott]

that was their point you cant just tap into the tach signal. if you buy the converter thing it'll work.

[Ramius83]

Would this MSD Tach Converter Box work for what I need?

http://store.summitracing.com/...h.asp

[Wulfgang]

I think you should bug Harlan about this. IMHO no company's aftermarket electronics should ever, EVER interfere with OEM electronics.

Regardless of whether your shift light is reading the tach signal correctly, it should not affect your tach. Especially when it only costs $0.10 to buffer the signal. Sounds like a brain-dead circuit design to me.

[Ramius83]

Wulfgang: Considering it is the shiftlight, anything I can do about this?

Will that converter work for this application? Or should I just go ahead and buy another shiftlight from Autometer or something of that nature?

Harlan has quit selling his products for the past year now, so his customer service will be nada. I am only using this shiftlight at this moment because I have it and don't have to buy another one lol, being cheap here, I know.

Thanks for the help.

[Wulfgang]

You could buffer the signal, but I doubt you would want to go through the hassle. Surely there are other shift lights out there that can be used with DIS.

[Ramius83]

Buffering the signal? What is involved in this?

[Wulfgang]

Nothing more than putting a buffer (an op-amp) in series with the tach signal. The buffer input is high impedance so that the signal is not affected. The buffer output can be low impedance to match the shift light input. If you are not familiar with the concept of a buffer, then as I said before, I doubt you would want to try this. My point was that Harlan should have done better buffering of the tach signal. If he is out of business, then there's not much you can do.

But you've got a 26, right? So you should have the cash to get a decent shift light!

[GTR Shop]

If you remove the s/light from the circuit, does the tach function correctly?Sound slike your install was donewithout a pullup resistor.10k resistor across 12v and tach wire should fix it.