Heres the dilema. To get more out of my igntion system I decided to wire in a relay so that when you hit the ignition it activates the relay giving the balast resistor the full voltage. Checked it on a voltmeter and it gains a full volt straight away from about 12.5 -13.5 and on the other side of the resistor from 9.2 to 9.9 (note: measured at idle). So it works. Runs fine and dont know whether or not its in my head or not felt like it started even quicker and felt like abit more mid range response. Now the problem, NO TACHO which is obvious because it gets its signal from the same igniton wire that goes to the resistor.

How can i get the standard tacho to work with the relay directly connecting the battery to the coil?

I have tried a couple of things but ill see what people say first before i comment more.

Thanks

If you understand how the tacho works, you shold be able to put 2 and 2 together and realise what you need to do to make it work again.
Once you work it out, make note;
If you use ####ty skinny wire, be prepaired for more voltage drop.

The best way to Beef up your spark is to make sure the coil negative has a good earth

I can make the tacho work fine by putting it to + coil. The thing that concerns me is that in a 1200 the tacho is getting the reading from the ignition wire is it not. Well thats the way read the wirring diagram and the way it seems to work in practice.

Is putting the ignition wire to positive coil cutting out the resistor.

Im not attempting this for miracles just the same principal as putting a relay to the headlights. Just an attemt to cut out voltage drop through the lines.

The tacho picks up its signal from a loop of the coils ignition supply.
You have now put a relay.
Whats the ignition supply wire for the coil now? Put 2 and 2 together

if or tacho is a original one ,this setup that you made dont work very easy.
the original 1200 tachometer is conected in serial whit the power that goes from the ignicion key to the resistor and to the coil.
since you put one relay ,i presumed that you take the original wire from the ignicion key the atack the relay.because of that the tacho measures the relay and not the ignicion coil.
you got to put the tacho in serial whit the relay and the coil to measure the rpm,s
conected the relay to the batery.the output off the relay must pass to the tachometer and then conected to the resistor and to the coil.
this is valid to the original tachometer from 1200 and 120y models.

maybe it's me, but what did does the realy do? Why not get a newer coil with a higher output?

If it's bypassing the old wire that helped, maybe it's time to freshen the electrical wiring?

Its all worked out now but just to answer b120sleepers questions. A is relay connects is used to connect a wire when activated by another. A common use for a relay is to connect the battery straight to what ever it is you want to power to cut out loss across the system (wire=resistance) The closer the connection the more power. All i wanted to use the relay for was to instead of having the power go from the battery to the ignition switch then back to the coil was to have it activate the realy giving the coil power straight from the battery.(about 30cm of wiring compared to 1.5meters and without having to go through the ignition switch. Saves a fari bit of power.

Just like headlights. No matter how good your wiring if you dont have a relay directly joining them to the battery you will notice the are dull due to power/voltage drop across the board.

oh now i understand why you were doing that. It's important if you have a big voltage drop from the wire. I'm amazed how the datsuns seem to not have relays for all the things ( headlamps, ignition ) that you'd just expect to include when wiring a car.

hi all.
my knowledge very limited

a stupid question here.. hope someone can help

may i know where is the coil?
is it the round thing 'before' the distributor?
(which have wire connects to the center of distributor)?

thanks

yep