3SGE in AE101 - Rev counter

[JT]

Bought an ae101 with a 3rd gen 3SGE, link ecu

How much work to get the factory rev counter wired up? Links to any diagrams would be great.

I've got an ok understanding of electronics and engines, but no experience in this particular area

Thanks

[GDII]

You would need to find the correct wire off the igniter and run it to the rev counter wiring in the gauge cluster.

[matt dunn]

Depends on what Igniter it is using?

I would guess that it is not using the Toyota igniter,
as they have a dedicated tach terminal output to run it.

[Stu-]

Which link are you using? If G3 or above you can run it direct from the link (if you have a spare aux output) and you only need to change the resistor in the tacho which is easy

[JT]

It's an older link, haven't worked out which yet but I don't think its a G3

Found a Mallory Hyfire 6A Ignition system wired in. Reading through the manual it says it produces a 12 volt square wave, 20% duty cycle.
Are there any cheap available tachometers that can run off this?

Alternatively I can buy a Mallory adaptor to hook up the standard ae101 gauge. From what I've been able to find, this originally saw a negative feed off the coil?
About $100 for the adaptor shipped to NZ.

[Stu-]

Pretty sure those systems still run a single coil? Try running a wire from the coil negative and see what happens

[Grrrrrrr!]

Don't run a wire from the CDI coil to the dash.. much badness could happen when 400V hits your tacho

Look for a yellow wire coming from the mallory box.

[Stu-]

That mallory wiring schematic is quite different to the one I saw so yes don't do that.

Most Toyota single coil setups run their tacho signal direct from the coil negative and most run in the vicinity of 200-400v standard ie a high level drive - that is why there is usually a ~38k-44kohm resistor inside the tach circuit board. Its this resistor that you swap out if you run the tacho from a 0-12v low level drive ie Link output. You use ohms law to work out the new resistor required and swap out accordingly. Its more likely the amperage at which that 400v is driven that would kill the circuit being as the Mallory is an upraded system.

So, to run your tacho, use the tacho output from the Mallory unit then use ohms law to work out how much smaller the resistor in your tacho needs to be. Find out the original resistor size by measuring it/checking the coloured bands and go from there. Can explain the calcs if you need them. Have done this many many times making Toyota tachos work from aftermarket ecus with low level drives.

EDIT: Didn't consider the 20% duty cycle mentioned in an earlier post - is that adjustable? You may need to fiddle with this to make it read correctly. Maybe just run it from the Link instead. Use IG3 on the LEM units and select tachometer in the configuration. It will drive one output pulse per spark event ie 100% duty.