VDO Tach: Pin1,3,4 Labeling

[richemj]

Can anyone tell me the wiring designation for Pin 1,3,&4 for a '73 VDO tach are? I can't seem to find a wiring diagram anywhere in past posts or on the internet.

Option1:
Pin1: Negative
Pin3: Tach source
Pin4: Positive

Option2:
Pin1: Tach
Pin3: Negative
Pin4: Positive

Both the red and blue/yellow wires have 2 leads into a common female end for connecting with the tach. Pin3 was a single black. I made a diagram of what wire went to what plug before disassembling.



I am trying to wire-up a tach I had refurbished and added voltmeter. Below is a pic of the backside with thick red-pos, black-neg, green-tach, thin red-highbeam.



No highbeam going back in so that line will be dead. Get no reading from either voltmeter or tach from Options 1 or 2 from above.

Car is a 3.2 conversion thus assumes the signal comes from Motronic versus CDI. The wiring in the diagram above worked fine on the '73 gauge before pulling it out for refurbishing. Perhaps the new guts with 4-6-8cy options can't read the motronic signal? Strange, volmeter doesn't work regardless if pin1/3 (blue/yellow-black) interchanged. Signals and bulbs work on the gauge, thus think it is a power issue with the tach internals with volmeter hardwired to them (tach doesn't work thus volmeter wouldn't work)

Maybe related...ignition off, tach lights come on (as other gauges) when main light knob pulled. With ignition on, tach light on by default, turns off when main lights turn on (all other gauges on).

Thoughts?
Many thanks!

[manu72S]

Hello from Le Mans

It is

Pin1: Positive

Pin3: Tach source
Pin4: Negative

[caproader]

From the obscure trivia and general comments department:

It is my understanding that any terminal labeled 'G' on the instrument is not Ground/Grund. It is 'Gabe' from the german 'give', as in: "this is where the electrical signal from the sensor (oil level or whatever) 'gives' in to the instrument.

Don't ask me how long it took me to figure that one out.

John

73 S with sporto and 69 912 now out of rehab

[richemj]

Thanks guys. Figured out the 37yr old wiring Gremlins. Runs great!