Factory Tach Wiring

[rklein383]

Ok,
I am working on my dash for my 69 383-s. I have always had an aftermarket tach (25 years) placed in front of the factory tach.

I don't even know if the factory tach works. I have located the two wires that connect to it. One is a dark blue with tracer that supplies power from the fuse box. The other is a gray wire with tracer that goes through a grommet in the firewall by itself and should go to the negative side of the coil.

The question I want to know is. What terminal does each wire go to. I took the tach apart and I am not 100% sure the spade end went to the right terminal and I don't want to fry a perfectly good tach if I hook up the wires incorrectly. One lug is brass and one is steel.

Does anyone know for sure which wire goes where?

 

[rklein383]

Found this after I posted the question. The longer stud going to positive switched makes sense as the connector pushes on to a bare stud and needs to be longer.

03-09-2010, 10:57 AM
The Spade terminal on the back of the tach goes to the negative side of the coil (signal) gray wire.

The longer stud goes to 12v switched power. (blue harness,goes to fuse block for acc.)

The case is ground.

My experience with the "Real Time Egineering" circuit board, is that all it does is make the pointer "move",so most people "think" they fixed it, I've checked probably 50 tachs using those, and "All" of them were inaccurate,
and if you have a bad Meter,it won't work at all!

I used to work at Redline Gauge Works www.redlinegaugeworks.com feel free to contact me regarding gauges/tachs/clocks.

 

[rklein383]

Well, the original tach doesnt' work, at least with electronic ignition. Some people say that it wont' work with electronic and same say it will.

Who really knows?

I re-installed my old tach and it works, so I guess I will keep it.

On the brighter side, all my light bulbs work now!

 

[mitch340Duster]

My '70 340 factory tach works. I have the RTE circuit board and I converted the car to electronic ignition (Chrysler orange box).

 

[RedFish]

The factory tachs do work with Chryslers electronic ignition. They may not work right or for very long with some aftermarket systems like MSD.
The factory tach has a small board inside with both contacts on it. It will pass through the housing in either position so the housing wasn't marked which is which.
My personal method of remembering is short = sender. Both start with S which is the sender marking on most other instruments.
When I add a chassis ground wire to a rally panel it is attached to the lower 1 of the 3 screws at that center pod whether there is a tach, or clock, or just a blank in there.

 

[rklein383]

I don't want to spend the money to get my tach repaired or replaced. Heck, the thing is too small for my liking anyway.

I have always liked a bigger tach hose clamped to the steering column.