The Stovebolt Site Forums The Shop Area The Electrical Bay 1966 electro-tac 4 wire wireing

hello - i have a electro-voice electro-tac
RPM 1000 tac in the insturment guage display.
it has not worked as far back as i can remember.
it has 4 wires.
black
white
and 2 wires together - like small gage speaker wire with webbing between them to together.
the way it looks under the dash is-
the black is hot
the white is ground
and the 2 wire speaker wire go into the engine bay.
the 2 wire affair has one silver and one copper wire.
i tryed the one of them on the neg/coil and the tac bounces around 6,000 (max) when starting but once started it rests at zero.
then tryed the other and it wont start at all. with motor running and touching the neg/coil with this wire it actually kills motor.
so that is where i am at -
has anyone seen these 4 wire tacs ?
and know how to wire it correctly - or have any thoughts.
thanks
paul

Don't the early tachs require a sending unit? What make/model is your tach?

SimS

hello sims
thanks for reserecting my question. i thought it was going to fade away.

this tach fits perfectly into the spot on the rt. side of the instrument cluster.
on its face it says
electro-voice electro-tac
rpm 1000
it goes from 1-6
it looks factory in its install but i dont think it is- though not sure on that.
i have done some searching but cant find any info on it.
this tach has been in this c-10 since at least 68.
the best i can do with it is hook it up...start it... but the pointer just spikes to its max and just bounces there.
i keep scratchin my head ... onit.
hopein i eventually will figureitout.

Some tachometers connect to both primary terminals of the ignition coil, but I don't know specifically about your tach. What did you do with the other tach wire in the twisted pair? The older Sun tachometers used a transmitter under the hood, with two wires going to the tach head, but I don't remember if those were twisted. My first thought is that they were not twisted. The fact that you have a twisted pair going to your instrument leads me to think the pair connects to both sides of the ignition coil. But that is a guess at this point.

Which wire did you have connected to the coil, and which one stopped the engine when you touched it to the coil? And to which terminal did you touch it?

If the tach head, the instrument part, has no electronic circuity inside, it probably needs a transmitter to connect to the igition coil. If you find electronic parts inside the device, those most likely replace the external transmitter, and the two wires in question would connect to the ignition coil. Silver and gold colors might indicate negative and positive- but also a guess.

Harvester

hello mr. harvestor
thanks for the input
well the blk is going to the fuse box
the white is a short lead with a donut connector.
the other two wires come off the tac terminals. its speaker wire. thin gage. one copper one silverlike in composition. these pass into the engine bay.
with one wire on the neg coil it just bounces at its hilt (6K).
and if i put the other wire on the neg coil - it wont start.

in googleing this type old style v8 tach -i have seen 4 leads .
one hot, one for a light bulb (or a ground if the tach itself is not grounded)
then like i said 2 threaded into the engine bay one to neg coil one to batt ground.
but you are right i have also seen a type where one goes to the pos coil as well !

its educated guess with out a diagram.
guess i should try the one wire to the batt and/or pos coil.