Hi all

I'm trying o get my smiths tacho to run correctly by taking the signal going from the mega jolt to the coil pack ( going through the diode arrangement) but I'm only getting half the revs reading. So I replaced the diodes thinking maybe there a faulty on but I'm still experiencing the same problem. Any one got any ideas ?

Ryan

Try the feed from the EDIS or the feed from the Megajolt
Have you wired your diods correctly? One should be a zenner diode



[Edited on 15/4/13 by snapper]

Hi I tried coming from from both the edis unit pin and the tacho out pin from the mega jolt and neither of them work.
This is the only way I get any kind of result. I'm currently having to use shift lights for a rough guess were my rpm is.
I'm pretty confident iv used the right diodes as iv wired in diodes to another car and that one is working fine although its running a standard ford clock pod.
Seems strange that I only get half the revs showing

I think I would start looking at the gauge now
It's probably internal wiring not compatible
Try wiring gauge to one side of the coil pack, then the other
If still half revs I suspect the gauge may sense a different wave form
Do check your diodes if one is the wrong way round you'll only get half the pulses

Ok sounds sensible to me . I'm off to get some more diodes today and double check it all over.
I have heard that some of the old smiths gauges don't like being used in this way.
Thanks for the advice

Easiest, but not the cheapest thing to do is get John Ostich at JDO Instruments to mod your tach to take the megajolt signal. He's done 2 for me now, one for the MGB the other the E Type.

Like I said not the cheapest, but the best solution.

Ok guys its sorted.
I was barking up the wrong tree the whole time.
It's a smiths RVC type tach so it connects into the tacho out put from the mega jolt
Then you have to set the dip switches on the back of the clock as follows

1 off
2 off
3 on
4 on
5 on
6 on

Finally sorted thanks for all the help guys

( got some spare diodes now too )

Glad it's sorted
I was unaware it was That type of Smiths
I have similar made by Caerbont and have run that off the diode pack and the Megajolt on different occations

I wasn't aware either until I popped a grommet off the back and saw them.