Needing help troubleshooting my instrument cluster

[Ben nelson]

Hey everyone, I have a 70 super bee project car and I am trying to get the factory gauges working on it. I have a few questions.

how can I bench test the clock and tachometer? They have never worked in the car as long as I’ve owned it.

what is the small red light that has something to do with the brakes on the lower left corner of the cluster? What’s it for and how does it work? I am trying to make the car as original as possible.


Any help appreciated, thanks.

 

[BeepBeepRR]

You should get the Shop manual for the car if you do not already have it. You also should know you need to be careful throwing 12 volts to the cluster as a few items use 5 volts. There is a little can looking voltage limiter on the back side of the cluster. That is your 5 volt limiter which is for the fuel and temp gauges. Be careful to not hit those with 12 volts or you risk frying the gauges. If once you download the manuals and schematics below you need help post back and ask your questions.

I am not familiar with the Rally dash or its components. I assume you are talking about the clock and tach combo.


Here is the downloadable shop manual. https://www.mymopar.com/downloads/servicemanuals/1970_Charger_Coronet_Service_Manual.zip
Here is the electrical schematics for your car. https://www.mymopar.com/downloads/wiringdiagrams/1970Wiring.zip

Wiring A

Wiring B

 

[BeepBeepRR]

Found this picture of the back of a tick tock tach. The grey wire is your tach lead. And goes to the negative post on your coil under the hood.
Orange is usually a lighting circuit but this one has a red w white tracer on the same terminal. Not sure on that. Looks like the Blue wire may be your 12v side. And as always check your grounds and when you are done check them again. Use a tester and check to see if the Blue wire is in fact 12volts. Pretty sure the red/white and orange will only have power when the lights are on.

 

[Wietse]

The clock should work when it gets 12v, the metal body of the rally dash is used as ground.
I ran an additional ground wire from the back of the body to the car body to ensure proper grounding as it is obviously important for everything to work.
Once that same 12v is present, and as mentioned by BeepBeepRR, the grey wire is secured on the coil negative pole it should read the rpm.
The small red light is an high beam indication, it gets a source from the foot switch for high beam.

Study the wiring diagrams provided above, they are a very good tool to identify and troubleshoot the electrical side of your car.

 

[Wietse]

The gauges for oil press, coolant temp and fuel gauge are provided with max. 5v by the voltage limiter mentioned by BeepBeepRR.
These gauges work on resistance created by its sensor, below is a link to another topic on this matter, do some searching as there is a lot of info on the forum about these rally gauges.

https://www.forbbodiesonly.com/moparforum/threads/bench-test-rallye-gauges.165005/

 

[Sixpactogo]

what is the small red light that has something to do with the brakes on the lower left corner of the cluster? What’s it for and how does it work? I am trying to make the car as original as possible.


Any help appreciated, thanks.[/QUOTE]

That red light on the lower left corner is your brake light.......It serves two purposes.
1. It will light up when your emergency brake is on along with the ignition.
2. It will light up when you have a difference in pressures between your front and rear brakes telling you there is a problem.

Also, If your gas gauge and temp gauge work, your voltage limiter is doing it's job. Clock runs on 12 volts but those clocks seldom worked very long even when they were new. Probably needs a quartz movement update. As for the tach, could be a bad sender, broken wire, bad connection or a few other issues. Need to do some verifying.

 

[Wietse]

Ah you are on about the brake light (you said small red light )
Sixpacktogo already said it all.