Wikid79Sa

iTrader: (3)

Well, my 79 SA has a new motor in it and the only thing keeping me grounded is the tachometer. I will try to be as descriptive as possible. I have beenn trying various things for several days now and have become quite familiar with the wiring diagram. Here goes:

Points distributor was swapped out for electronic one and worked fine before engine bay teardown and cleaning.

Now-
Tach reads voltage until engine starts, then it sits at zero.
While running, there are no warning lights.
Voltmeter/tach read 13 volts, while voltage at battery is at 12.40 volts.
Leading and trailing ignition is firing. (engine runs, but has what sounds like a slight miss.
Voltage regulator is brand new.
Coils each have 2 wires running to + side and 1 wire on the - side. This has been verified by the conversion writeup on this site. (+ to + side of igniter, - to - side of igniter. )

If I can think of anymore details, I will update.

Does anyone have any suggestions? I did some harness trimming to eliminate rats nest components, but was very meticulous and used the wiring diagram to verify.


Thanks,
Rick

Wikid79Sa

iTrader: (3)

I also measured the voltage drop from the battery to the coils and ignitors and it was less than .2 volts.

mazdaverx713b

iTrader: (91)

have you considered the tachometer itself to be faulty? if you have a spare it might be worth installing it to rule out the possibility of a faulty unit. my guess would be something is not completely correct with the installation of the electronic ignition swap.

where in OH are you located? if you are relatively close i may be able to swing by and lend a hand.

2GSLSE

iTrader: (6)

I saw the same thing on an all original SA recently try cleaning the contacts in the fuse panel (I think it was the one on the far right) the one I saw was actually hot on the ends due to resistance as soon as I wiggled it the tach came alive again.

Wikid79Sa

iTrader: (3)

I'm located in Akron and would gladly accept any help. Name the compensation (beer, gas money, spare parts)

mazdaverx713b

iTrader: (91)

no compensation needed. you are about an hour from me.

j9fd3s

iTrader: (3)

on mine the connector on the back of the gauge cluster is a little flaky, every time i pull it off the trailer the tach doesn't work right away, but then once its working, its fine.

basically the tach is driven directly from the coil, so there is a wire on the coil (i wanna say the leading + side on an SA), and it goes right to the tach, no connectors or anything, so its really simple

Wikid79Sa

iTrader: (3)

I will try the connector on the gauge cluster when I get home. The simplicity of the tach connection is why it is so annoying.

And mazdaverx713b, I'll let you know what happens after I tinker with it tonight.

13x

just an idea ... it happened to me once ... the tach gets the input from the trailing coil ... there is a wire with a females spade connector that had back off (or I somehow pulled off) ... once I reconnected to the coil the tach began working again and has worked since

DivinDriver

iTrader: (15)

Leading coil on an SA (due to the ignition control system on US SA's)

13x

DD even the 79 with points setup?? (perhaps was the S3 I had the issue on but thought they were the same)

wiked79 check em both lol

Wikid79Sa

iTrader: (3)

Tach is back! I swear I had seen that the tach signal comes from the + of the leading coil. So, I decided to put the YG (tach)wire on the - side and the GR wire on the + and voila. Just goes to show ya......

Thanks for all the feedback, this board is a wonderful resource.

Who wants to grab some beers and wings to celebrate??

DivinDriver

iTrader: (15)

Yep; per the 79 wiring diagram, neg side lead coil.

Tach has to go to the neg side because that's the side the points (or ignitor) switches in order to make spark. The Pos side is constant voltage when the ignition is on.

On SA's some builds (all but Canada, I believe, but Cali for certain) disable the trailing ignition under certain engine conditions for smog purposes. If you hook the tach to the trailing coil, it will switch on and off too. Very maddening thing to deal with if you plug it wrong.

mazdaverx713b

iTrader: (91)

i'm down for grabbing wings and beers! also, i'm having a meet at my place on june 9th and any 7 owner is invited. here's a link with the details: http://www.ohio-rotaries.com/viewtopic.php?f=5&t=594