Last night I got my Harlan Rpm switch in for my MEVI. I wanted to play with it so I went to Radio Shack and bought a LED to use as a shift light in the meantime. I took out the gauge cluster and looked for the "red and yellow" striped wire to tap into. There were two so I checked them and neither was the Tach signal. According to Maximadriver.com there should be a TAM screw (there isn't on my '99).
Finally I went to the 5th Gen forum and found their tach line is green and white. I checked the green and white wire and that's what the 1999s use for the tach.
After hooking up the rest of the wires for the Rpm switch and LED I hit another snag. After grounding the wire the Tach goes to 0!! The shift light works fine, but the tach continually sits dead on 0. So now for some reason I can use either my tach or my shift light
Does anyone have any ideas why this might be?
-hype

 

Someone has to have done some shift light work and had a similiar problem. I just don't understand why the tach signal doesn't reach the tach when the Harlan is hooked up. The Harlan is wired in parallel, but the signal should still get to the tach.
-hype

 

Try wiring it directly to the #1 coil wire. Strange, the rpm switch should only have 3 wires (assuming its like the shift light), red for power, green for signal and black for ground. Are you saying that after you found the 12v for the red, then used the green/white wire for the signal, that whenever you ground the black wire either the tach or rpm switch works? If you haven't already done so ground the black wire to one of the 10mm bolts under the dash and tap the green wire into the #1 coil. This should fix the problem.

 

The rpm switch has 4 wires, the 3 you mentioned plus a fourth switched ground (ie signal) output to trigger a device (in our case, the VIAS solenoid). That output wire is "hidden" inside the shift light to trigger the light, so you don't see it.

 

For my wiring the Harlan has 4 wires total. Red is connected to power, Green is connected to the tach signal, Black is ground, and white runs to the ground on my LED. I hook up the red, green, and white wires first and my tach still reads. As soon as I ground the black wire for the Harlan the Tach drops to 0, but when I rev to 2000 (what I set the Harlan at) the LED switches on. I definitely have the Tach signal wire, but I can't figure out why the tach and Rpm switch don't share the signal. For some reason the Harlan steals the signal totally even though it's wired in parallel
-hype

 

That's strange. So the harlan works but the tach needle becomes inoperative?

All I can think of is maybe there is a grounding problem. Where are you taking the ground for the Harlan? I splice the 12V and grnd into the lighter. I just don't know...

 

Correct. When the Harlan becomes powered the signal no longer reaches the tach.

Quote:

All I can think of is maybe there is a grounding problem. Where are you taking the ground for the Harlan? I splice the 12V and grnd into the lighter. I just don't know...

I took power from the fuse box, and I grounded to a screw near the fuses. The way I see it a 12v is a 12v and a ground is a ground. I tried changing sources, but it didn't change anything.

Mishmosh, did you wire your Harlan in parallel from the tach wire? I was going to tap from the ECU, but my colors were different. That's why I went to the cluster where I could test the wires before tapping. My green/white wire is on the far right connector when looking at the gauge cluster right side up from behind. The connector is closer to the speedometer than the tach, but it definitely gets a tach signal because the Harlan works when wired to it. I just can't figure out why the Harlan works, but the tach stops getting the signal when the Harlan has power.
-hype

 

I have a 95 so there is just the simple matter of looping wire around the TAM screw. Definitely in parallel, both cluster and Harlan are seeing the same voltages, but the only way I see the Harlan "stealing" signal is if the input impedances were GROSSLY mismatched in favor of the Harlan. I am going to assume that the Harlan is working properly (though this is not 100%). If the voltage drop to your ground and power read 12V then those are correct. That really leaves the green tach wire... Damn, it's kind of frustrating that the 99's are so different but I think that if you find another suitable tach/coil input, you will get it working...

 

tap the tach signal from the ECU.

 

Thomas that's basically what I did. I tapped the wire behind the gauge cluster, but it's the same wire that comes out of the ECU. I guess I can try going straight from the ECU, but I don't think that'll change anything.
-hype

 

mine's a 99 and tapping the ecu works fine.

 

Ok after more help from Thomas I decided to tap the tach signal coming directly from the ECU. The pin on a '99 is actually pin #5 and it is a green/white wire. I tapped off of the ECU connector harness and ran the tach signal to the green on the Harlan. I then grounded the Harlan and I have the same problem As soon as the Harlan is grounded the tach goes to 0, but the Harlan works when I hit the specified Rpm. The ground is obviously good because the Harlan works, but for some reason the Harlan interferes with the tach's ability to get a signal.
I've never had such a strange problem when wiring before
-hype