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MS3x + stock tacho, in a car that had no tacho in the first place

kingkong

New member
Joined
Jan 3, 2017
Location
France
Hi all,

I installed a tacho that came from, apparently, a 240 dash, in my '89 244 that came with a B200E.

I have two questions :

1. Is the stock harness already equipped to have +12v and ground ?
2. where do i plug the tacho output cable from the MS ?

Thanks guys.

Here is the thing :









 
Last edited:
The tach on my '85 looks a little different but I expect it's has the same wiring. There are several pins that stick out of the tan circuit board that the tach assembly plugs on to. These pins provide power and ground to the tach. The top 3 spade connectors on the back of the tach are used with an extension cable to connect to a small dashboard clock (since the tach replaced the big clock).

The bottom 2 spade connectors are wired together inside the tach. Connect either one to the MS3x tach output signal - I'm not familiar enough with MS3x, but the tach signal needs to be a 12v output. If this doesn't work, you'll need to add a cube relay with the flapper removed to generate high voltage spikes for the tach -- deeworks has a nice picture of a modified relay, but I don't know if it survived the photobucket issues. http://forums.turbobricks.com/showthread.php?t=311116
 
I have an 82 and I plug into the original tach spade connector directly from MS with no modified relay. I have heard many people say they need to do a modified relay for the higher amplitude signal.
 
I think with MS1 you had to put a pullup and a relay and whatnot but now MS2 et MS3 generates a +12V signal so you can technically plug it right to the tach.

I will try and let you guys know how it goes for MS3x.
 
I'm definitely interested in this result, because I've been putting off making the 'relay circuit' to get my tach working. If I just have to plug the tach-out into the cluster, I'll be very happy :).
 
For reference, I did it straight from MS to the tach for both microsquirt and ms3 pro. It worked the same way for both.
 
One more on the list of people who just hooked it straight up to the tach, no little relay guts needed. I think it's the 700/900 series tachs that needed the relay to juice the signal up some.
 
As I swapped to COPs I found that I didnt have enough I/Os to run a tach directly off the MS2 box, so after some digging, I found that a set of diodes off each of the coil trigger wires daisy chained into one gives just about high enough spikes to drive an aftermarket tach without the relay guts. This way you can leave your ms tack output pin for something else. With ms3 its probably not a problem since you have way more IOs to use, but if you feel like you're running out of IOs its an option.
 
I guess I know what I'm testing when I get home! :)

...if I can get the car started. It's been garaged for months due to -20*C winter. Time to work on the cold starts!

Check the MS Testmodes menu - it might have the option to pulse the TachOut pin fast enough to register on the tachometer without needing to start the engine.
 
It started up just fine, but it looks like I'm going to need the tach adapter circuit. I'm running MS2, with the FIDLE output as my tachout wire...but the pulsing is not enough on it's own. My multimeter shows activity on the FIDLE wire, but it's moving too quickly to register accurately on the meter. I'm running a three-wire Subaru waste spark coil, but the -VE poles are buried deep in the poly casing, otherwise I'd have tried that diode circuit too.

I took the opportunity to do some warmup autotuning too, so it wasn't a wasted trip to the garage, haha.
 
Just checking - do you have a pullup resistor on Fidle? 1Kohms to +12v would be good. Without this, the Fidl pin will stay close to 0volts.
 
And you can build the diode circuit on the board. Just find your spark output pins, attach the diodes and then link them, then another diode, then attach to a wire that runs to the tach.
 
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