67 Impala Tach Dash - Impala Tech
Electrical & Wiring Troubleshooting electrical problems

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post #1 of 5 (permalink) Old 11-19-2016, 12:00 AM Thread Starter
Join Date: Jul 2013
Location: Australia
Posts: 13
67 Impala Tach Dash

Having a few issues with my dash that I can't seem to figure out. I just had my factory tach dash completely gone through and restored and have installed back in the car with a few issues.

1. Can't get the park brake light in the dash to work at all. All the wiring is factory wiring and I have checked everything is installed correctly. FYI everything else in the dash is working 100% all lights, gauges etc and switch on the pedal assembly is good. Is it possible it is not getting power somehow?

2. The mechanical oil gauge pegs past 'H' on the gauge. I know the engine, oil pressure etc are all ok. I have simply run a copper line from the block to the back of the gauge. The engine is a 350 SB which is not the original engine. Is this a normal reading?

3. The tach is only intermittently working. When it does work it reads correct, however will just stop at any random time, usually while cruising. Have MSD electronic distributor and blaster coil with tach wire hooked up to grey tach wire coming from distributor as per MSD instructions.

Any help with these issues much appreciated.
dsikkema is offline  
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post #2 of 5 (permalink) Old 11-19-2016, 08:13 AM
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Join Date: Jul 2006
Location: Estero, FL
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1. Unless the under dash wiring harness and the printed circuit overlay on the back of the cluster is new, you could have a break in either one of those.
2. The engine could have had a high pressure pump installed (which is not needed) or the gauge is bad. Check it with an aftermarket gauge.
3. The tach will not work with an aftermarket distributor. It will have to be recalibrated.


1965 Impala SS 396
1967 SS427
Michael9040 is offline  
post #3 of 5 (permalink) Old 11-19-2016, 10:01 AM
Join Date: Jan 2006
Posts: 12,362
Quoting the instruction sheet, "

The MSD Ignition features a Gray Tach Output wire that provides a trigger signal for tachometers, a shift light or other add-on rpm activated devices. The Tach Output wire produces a 12 volt square wave signal with a 22.5° duty cycle.

Some vehicles with factory tachometers may require a Tach Adapter to operate with the MSD. For more information on Tachometers and MSD Tach Adapters, see the Tachometer Section on page 6.
If your GM vehicle has an in-line filter it may cause the tach to drop to zero on acceleration. If this occurs, bypass the filter."

Your tach probably needs the Tach Adapter.

Copper tubing will work harden from the engines' vibration and crack. This is why gauges ship with white nylon plastic tubing, not because the plastic is cheaper. An aftermarket mechanical gauge will tell you the pressure in psi, not low or high.

You need twenty or more psi at idle, and a ten psi increase for each thousand RPM above idle up until the by pass spring opens at sixty psi. Sixty psi is all the oil pressure that your engine will need to provide oil flow to the front main bearing of the engine. A higher pressure is just accelerating the wear on your timing chain and the gear on your distributor.

A High Volume oil pump (different from a high pressure pump which is made by stretching the stock oil pressure by-pass spring) is used on an engine built for high RPM operation by using a crank that has a chamfered cheek on the crank throw. The chamfer is used to keep the rods straight on the throw but has the result of narrowing the bearing and creating a internal oil leak. The high volume pump which has longer gears to increase the volume of oil displaced also puts a strain on the cam's timing chain and the distributor gear (which wears even faster if using a bronze drive gear) is used to compensate for this internal oil leak.

I use Autometer gauges, made in the USA and is a quality gauge.

Big Dave
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post #4 of 5 (permalink) Old 11-19-2016, 06:16 PM Thread Starter
Join Date: Jul 2013
Location: Australia
Posts: 13
Thanks for the replies. What are some tests I could do to find out why the brake light is not getting illuminated? Printed circuit looks good, which is why I'm stumped as I though it ran on the same circuit as all the other lights which are all working?
dsikkema is offline  
post #5 of 5 (permalink) Old 11-19-2016, 10:34 PM
Join Date: Jan 2006
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Turn ignition on and off. All idiot lights are supposed to illuminate momentarily so you can check to see if the bulbs are good. If it doesn't light up and all of the others do then pull bulb to see if it is good, or if the socket the bulb sits in is still good. There are two spring clips that contact the thick film that is your printed circuit behind the dash. If the tangs are bent or have cut through the film they will not work without repair. You can carefully, with a low wattage soldering iron, melt a glob of solder to bridge any breaks in the thick film.

Big Dave
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