4 tach terminals

[adsm08]

OK, trying to get my gen1.5 cluster wired up to a gen2 dash harness. I have lights, fuel, coolant, oil, and charging. You know, the super important stuff.

Right now I am trying to figure out the tach, since Ford does not seem to have ever written down the schematics for the 86-88 tachs. Looking at the circuit board I have 4 pins, B, G, S, and L2.

From my experience with after market ones I am assuming that B is a 12V reference, G is ground, and S is signal. Does anyone know what L2 and S are?

If I hook power and ground to the B and G terminals respectively I get a constant reading of about 400 RPM. If I tap a grounded wire to the L2 terminal I can make the needle respond and go up matching the frequency of my tapping. The S terminal seems to do nothing.

 

[adsm08]

Ok, got the tach to work. Kinda. It jumps a bit when I plug it in, turn the key on, and tap a pin at the PCM connector.

Still not sure what that L2 pin is for.

 

[RangerSVT]

Lights/illumination?

SVT

 

[SenorNoob]

IDK If you've got this figured out yet or not, but. The L2 pin (BTW, mine wasn't labeled. Process of elimination) is basically the 4cyl vs V6 switch. Ground that pin and the tach signal drops. Mine was ~1300 at idle and ~3000 at 55mph in overdrive with 3:73's. The gear ratio chart showed that to be way off. Now it's ~1000 at idle and ~2000 at 55mph in overdrive.

Edit: Not sure why, but the wire going to that pin had nothing after the swap. IDK about before. I just jumpered across L2 and the ground pin with a short piece of wire under the nuts that hold the tach in.

 

[adsm08]

I got it all figured out for the tach.

Still having temp and fuel gauge issues. Gonna look more into those tomorrow.