Tachometer wiring harness help. Brown wire?

[jmillsUT28]

Hey guys, I bought this blazer a few months ago. Doing a full restore on it. It did not come with a tach from the factory but the last owner switched out the gauges to one that had a tach. He did not wire up the tach but had the tach wiring harness.

Here's a picture of what I have. Is this all I need to hook up the original tach? I would think the pink wire would hook up to the distributor. Where does the brown wire go? It has the original distributor in it I think.

[IMG][/IMG]

[GMCPaul]

Pink wire to ignition unfused terminal on fuse block, brown wire to negative post on ignition coil.
Paul Jr. @ GMCPauls

[jmillsUT28]

Well just looked. I have a HEI distributor on this one. From what I have read is that there is a battery and a tach plug on the HEI. Just don't know where this brown wire goes.

[GMCPaul]

Then you'll need to cut the terminal end off the current coil wire and get a connector for the HEL distributor tach connection. Be aware

In regards to HEI use a stock style replacement tachometers they are already compatible UNLESS you are using some of the cheaper made Chinese HEI control modules. The real underlying problem with the tachometer not working in these trucks with HEI ignition is the output of the module from the HEI. The tachometer signal can be distorted either by peak size (causing "bouncing readings at idle and then smooth's out around 3000rpms) or funky square waves of various sizes- signals that do all kinds of things to your tach readings, to very low fat rectangle waves that don't do hardly anything. It's the modules design and output that is the problem.

Many of the inexpensive HEIs and/or replacement modules will cause these problems to happen, as well as these modules are NOT designed for performance use period. In our experiments with several modules the cheaply made and older type will severely reduce voltage output at around 4500rpms too! So, it's not only the distributor...it's the module and coil too that play a part in total performance and certainly tachometer compatibility.

Most "performance" HEIs have it all....great coil/module output to 6500 rpms and complete tach compatibility. Plus, if you have a performance coil, don't just put a standard module in...you can burn it up quickly.
Some have great luck using different available tachometer filters to clean up the signal sent to the tachometer. We have not experimented with these so we have no recommendations in that regard.
Best HEI for compatibility we've found is the Actual GM HEI with GM internal parts all being OEM.
Paul Jr @ GMCPauls

[jmillsUT28]

Thank you very much for that info Paul!

[WorkinLonghorn]

I realize this thread is ancient but I just tried to hook up my OEM tach to the Skip White ($49) HEI distrib I've had in there for some time and there was no needle movement. When I tested the tach signal (brown wire attached to "tach" terminal on the distrib) with a digital handheld multimeter/tachometer, the readings were crazy- just random numbers very quickly changing. So this seems to be in line with what GMCPaul found while testing. -Brian

[tdangle]

I just did the tach upgrade. I have a JMR HEI and works perfect. Highly recommended as it fills up the blank hole and I got rid of the tach mounted under the dash.

[WorkinLonghorn]

Originally Posted by tdangle

I just did the tach upgrade. I have a JMR HEI and works perfect. Highly recommended as it fills up the blank hole and I got rid of the tach mounted under the dash.

I'll look into that. I have an original tach but even when it was hooked up to the old-style coil it was way off. Maybe I need new both (Distrib+tach).