EFI + Electric Speedo?

[johntennyson]

I'm looking at going to an electronic speedometer on my MkII. I've got the engine running the Mustang EEC IV EFI using the RM aftermarket engine wiring harness. I'd like to use an electronic speedometer, such as:

Vision Chrome 120MPH 4" Electronic Speedometer with Autocalibration, 12V | Speedometer | By Type | Instruments | VDO Instruments and Accessories

or

Auto Meter

(the VDO gauge costs $100 less!)

Am I correct in assuming that I can use the VSS for a '95 Mustang in my T-5 and just splice into the wires leading to it for the signal to the speedo?

I've heard that if the EFI CPU is not plugged into to VSS that the car won't run properly.

Also, the VSS is a Hall Effect unit, right?

Thanks!

[cobrathegreat]

There are 2 wires out from the VSS. It does not mater which one you splice into.
The car will run fine if not plugged to the the ECU.

[johntennyson]

Help- I got the Autometer 'cobra' electric speedo and a VSS for a '95 Mustang and wired it as per instructions, red to switched 12v, black to ground and violet tapped into one of the VSS leads (I've now tried both)...

... and no signal to the speedo. On my calibration runs, the odo just sat there doing nothing when it should have been running numbers and after the end of the run, the needle did nothing on the way home.

What gives? This is pretty frustrating 'cos between the reversing gearbox, the original mechanical speedo and this new unit, I'm into this for over $300 and still have no idea how far or fast I'm going.

I'm really close to doing this:

[AC Bill]

Is there no black box with your unit that needs to be wired in as well?

My Classic Instruments speedo had one that is used for the speedo adjustments. It has +/- buttons on it, to adjust the needle reading.

What is the violet wire from, your ECM?

[33ratrod]

I spiced both wires from VSS and ran to the speedo one + one - can't remember color but speedo works fine. They are still hooked up to the ECM

Rick

[Dan Babb]

Just asking the obvious question - do you have a plastic gear attached to the end of the VSS that goes inside the transmission?

[johntennyson]

Dan: Yep, the pink one. When I was fooling around trying to make the mechanical speedo go (forward!), I had the top end of the cable visible as I drove around the block and could see the core turning. I put that gear on the '95 VSS, so I gotta figure it's going around in there.

I just got back from driving the car around with the VSS disconnected and yeah, it ran fine, no MIL signal, despite the admonition here

Fuel Injection Technical Library » Vehicle Speed Sensor (VSS)

which said it might cut out on deceleration, which I took to mean overrun, as in going downhill. We have lots of hills here, and it ran fine. Hmmm. I'm waiting for the next round of email tag from Autometer's tech guy, but it looks like I can run the engine without the VSS and put Autometer's sending unit in there.

[Art Cuesta]

Through the years WIREDIET.com has received many questions about gauge hook up
and I can tell you that for the most part each gauge maker has their own design for the gauge circuits and hook up. Some require the makers sending units and even sending wires to be used. Some require auxliary parts kits or recalibration to make them perform correctly with a specfic engine or set up.

If a vendor recommends a particular gauge for your engine and setup that they say will work for you - they should be able to tell you what it's going to take to make it work right and how to hook it up correctly.

In my experience I've found Autometer and FFR (Speedhut, contact Speedhut not FFR) gauges to have good tech support but you've got to contact them and explain what difficulty your having with what engine and setup.

Art