could still use help with tach

[rb250sx]

So im still having tach problems. I have a S13 with sII rb25. Ive tested voltage at the plug of my cluster and at idle the signal wire is around 6.some volts. checked the ign wire on the plugs and the grd and all are good. ive used 4 tachs so far, the digital one that came out of the s13, an analog one from another s13, the RB tach and a tach that i took out of another digital s13.when i plug the s13 cluster in, the needle wont move at all. The RB tach was out of the cluster, when i hard wire 12 volts to ign and signal it wants to peg to 0 rpms. This tach is out of the cluster howevever and may not be operable. The tach out of the digital s13 cluster has 2 grnds on it, however there is only one connection for ground on the back of the cluster itself. when i hard wire this tach it does the same thing i saw with the RB tach (moves counter clockwise toward 0). Anyway, i know people have been driving around with the stock 240 tachs and just were getting inaccurate readings, but they were at least getting movement out of the needle, am i correct? If someone can help me or give me some kind of technical explanation for what im seeing it would be appreciated.

[Dramier]

On my RB25's ECU, there is a specific wire coming out that is dedicated to giving the tachometer signal to the cluster. It is the number 7 wire, sky blue in color.

Now, on an aftermarket cheapie Sunpro tach, you set the tach to six cylinder, and hook up the sky blue wire to the tach's signal wire, and you also hook up a 1k resistor inline with the wire. This will give you a read-out that is accurate to around 5500RPM and starts getting sluggish after that.

I know this doesn't address your specific tachometer problem, but it is at least a solution that will get you a working tach.

Good luck.

[kevsster]

I just put my RB tach into my S13 cluster (took a bit of cutting with an exacto knife but only took about 10 minutes) its not a perfect fit but it works. Then I hard wired the neccessary connections to the back of the s13 cluster. Then, I took the red/yellow tach signal wire from the s13 tach plug and hardwired that to the RB tach signal wire. Tach works perfect. Also, I pulled the orange needle off the RB speedo so that my speedo and tach both have orange needles. Feels like your gonna break it, but it should pop off. Oh and before I did this, my S13 tach didnt move at all either.

[rb250sx]

ok, ive been doing some more reading, and it appears that no one who has an 89-90 has gotten the tach to read due to it being SOHC. please correct me if im wrong. I would like to mod the cluster and put the rb tach in, but i had it out of the cluster when the car went through the fire, so i think it is damaged, because when i hard wired it up to the signal wire, it wasnt moving. Im thinking about just going with the LS auto tach now.