Tach Pick-up/Connection for Megasquirt

jschrauwen · Post by **jschrauwen** » June 12th, 2006, 9:14 pm

The only connection I'm concerned with for the install of my V3 Coilpack Plug n Play Megasquirt is the the yellow wire to the tach. The explanations I get from Probetalk deal with the wiring for the PGT and I don't think our wiring systems are that identical. Those of you that needed to tap into the tach signal, where did you get it from? I hope somewhere in one of the other connectors that are co-located near the ECU ... *fingers crossed*.

XxantwawnxX · Post by **XxantwawnxX** » June 12th, 2006, 9:42 pm

I used the instructions what came on the disk for the 2.5 lr probe. everything runs fine.

jschrauwen · Post by **jschrauwen** » June 12th, 2006, 10:15 pm

XxantwawnxX wrote:I used the instructions what came on the disk for the 2.5 lr probe. everything runs fine.

I got roughly the same thing on the CD that Ryan sent with the MS. Again I get the distinct impression that they are talking about the PGT when they make references to this colour and that colour connector here and above there and beside this or that. I could be chasing my tail looking for their specific connector while all of the time not knowing that the MX3's connectors and the like are not the same colour coding or located in the same gographical spot as they describe. Again, I'm looking to tap into the tach signal from a connector that is hopefully near the same location as our ECU.

BTW, nice video of your MS layout. Talk about one stripped down MX3 !!

XxantwawnxX · Post by **XxantwawnxX** » June 12th, 2006, 10:34 pm

hmm maybe if u have aim or sumthing can send ya whats on my CD...but it might be a lil diff i dont have coilpacks.

the color coing on mine was correct.

Rick Johnson · Post by **Rick Johnson** » June 12th, 2006, 11:15 pm

Just go off the ne1 wire. All the wires are in the exact same spots <of course, otherwise our ECU's wouldn't interchange> but the colors are pretty much all different <on my 92 anyways>. After the first 3 wrong colored wires I just quit looking at color all together and make sure your pinout is correct.

jschrauwen · Post by **jschrauwen** » June 12th, 2006, 11:51 pm

Rick Johnson wrote:Just go off the ne1 wire. All the wires are in the exact same spots <of course, otherwise our ECU's wouldn't interchange> but the colors are pretty much all different <on my 92 anyways>. After the first 3 wrong colored wires I just quit looking at color all together and make sure your pinout is correct.

That's the whole point Rick. With the Plug n Play there's no pin-out's to contend with. The KL31 ECU has already been tapped into with a multitude of wires going to that large 37pin connector that plugs directly to the MS. Coming out separately from the MS is another group of loose wires - Green, White, Red, Black, Yellow. The Red, White and Green serve as the triggers for the tripple coilpack (to be installed at a later date), the Black is Ground for the coilpack and the Yellow is to be connected to a Tach feed. Aside from hooking up the vaccum tube from the MS to a viable vaccum source, I can plug in my MS right now and not connect the any of those 5 wires previously mentioned and everything should be good to go.
I just like to find a Tach source that's located close to the ECU location. I'm hoping that someone may know which connector to go directly to for my 92 GS.

ariesdude · Post by **ariesdude** » June 13th, 2006, 2:40 pm

If you are still going to be using your old disty for the ignition - then you may not need the tach feed from MS - once you go coil pack you can probably splice into the Yellow/Blue wire in the disty connector - i think it goes directly to the tachometer -so if you can find it under the dash you can splice it in there - but before that it would be wise to make sure the tach feed from MS is compatible with the stock tach.

Rick Johnson · Post by **Rick Johnson** » June 14th, 2006, 12:23 am

Oh I didn't realize you had this plug'n'play unit, I thought you were buying Marlons BP megasquirt a while back?? I find it odd that it would require you to tap the tach wire, seeing as how it's plug and play and the info it needs is right there.

jschrauwen · Post by **jschrauwen** » June 15th, 2006, 4:02 pm

Rick Johnson wrote:Oh I didn't realize you had this plug'n'play unit, I thought you were buying Marlons BP megasquirt a while back?? I find it odd that it would require you to tap the tach wire, seeing as how it's plug and play and the info it needs is right there.

Actually, you're right on both counts Rick. I do have Marlons old MS that I should be selling soon and I also have the latest version Plug n Play from the Probetalk Bulk Buy. The Plug n Play as I just found out is truly a Plug n Play the way in comes shipped. The 5 wires that I queried about earlier were all designated to be hooked up when I decide to make the transition to the coilpacks (not sure as to that event yet). Apparently, MX6's and MX3's cannot tap into the tach from under the dash because there is an inline resistor somewhare and tapping in at that point would lead to the tach bouncing erratically. I've later been advised to tap into the tach signal at the disty itself and would like to confirm ariesdude suggestion of the yellow/blue wire on the disty. It's a 92 disty btw. Confirming this should tidy everything up nicely and should be looking at installing the new MS this weekend ...... *fingers crossed*.

ariesdude · Post by **ariesdude** » June 15th, 2006, 4:50 pm

The inline resistor is built into the internal coil in the disty i think - YEL/BLU was from grant's wiring diagrams....

jschrauwen · Post by **jschrauwen** » June 15th, 2006, 10:43 pm

ariesdude wrote:The inline resistor is built into the internal coil in the disty i think - YEL/BLU was from grant's wiring diagrams....

Ryan from probetalk has referred to a possible inline resistance that may be located somewhere within the wiring harness system and that by going to a lead from the disty I can prevent from creating havoc with the tach. Apparently, this isn't an issues with the PGT but only with the Mazda's. That's why I was hoping to track down another MX'r that had also got the Plug n Play version that included the coilpack option. I haven't looked at Grants wiring schematic for the disty as of yet and at times am a bit reluctant since there are a few subtle differences between the Eunos and MX3. I have shop manuals but at times it's not always specific as to it's termination as far as the disty may be concerned. Is the yellow/blue wire the only one known to provide tach info from the '92 disty?

ariesdude · Post by **ariesdude** » June 16th, 2006, 12:13 am

jschrauwen wrote: Is the yellow/blue wire the only one known to provide tach info from the '92 disty?

As far as i know - yes - and its the same for most internal coil disty models - infact i tapped into that wire when i did the HEI mod with external coil.
The inline resistor is almost certainly built into the coil i think - because i had to use an extra one kilo ohm resistor for the tach feed from the external coil - its been working fine till now.

If the MS tach output is too strong - you an use the resistor to tame it down - if not you can probably connect it directly to the tach. I would suggest using the resistor method first just to be safe.