1989 240sx: Help wiring aftermarket gauges

[Blackhat]

I got several new gauges and I'm having trouble figuring out a couple of things.

1) The water temp gauge works, but shows the temp higher than it actually is. I assume I need to put a resistor in there to change the signal but I'm not sure what size would be needed... Any ideas on how to figure that one out (I'd rather not do trial and error).

2) The Speedo has been one big nightmare. I can't figure out how the oem speedo got it's signal. I have the yel-blu and yel-blk wires, but not sure which is which. I have been assuming the yel-blu is my signal, but I'm stumped on the yel-blk. Maybe ground? or 12v?

3) Fuel level gauge also is a little confusing. I have a Grn-blu, red-blk, and black. I grounded the black and was thinking the grn-blu was just a signal for if the level got too low it'd signal the fuel low light, but apparantly I'm off somewhere in my thinking.

Well, at least the Tacho is working... of course, that one was easy. I'd do more trial and error on this stuff but I'm a little afraid of burning out sensors if I get it wrong.

[JDMClifford]

might want to look at the FSM for a whiring diagram.

[Blackhat]

I have and that's where I got the wire colors from. But unfortunately they just show two wires going into the speedo but no documentation on what they are. Same goes for the Fuel level sensor.

I was hoping someone else out there knows more about them or has done something like this before... surely I'm not the only one replacing the cluster?

[ApexRK]

for the water temp gauge where is the sensor tapped into the coolant system? and how do you know its reading wrong?

[JDMClifford]

what motor if its for the s13 sr go here
http://www.innovatemotorsports.com/r...Silvia_S13.php

[Max_PSi]

Do yourself a favor and get a test light. Its the best $10 you can spend when trouble shooting like this. It'll tell you what wire has power, and when.

[johngriff]

The speed sensor is a simple magnet based hall effect sensor. It stikes to magnets across each other and sends a pulse out. Both wires are the same. What is your guage asking for?

The Temp sensor is a 0-5volt.
The range is
-40F =5v
260F = 0v

So within that range the sensor will read.
What does your temp guage require?

Gas Gauge? I am stumped, always wanted to get into the workings of the signal wire, never found the time.

[azndoc]

Just curious what brand of gauges did you purchase?

[Blackhat]

ApexRK: It's the stock instrument cluster sensor. I know it's wrong because I have the 2-wire temp sensor hooked up to my MSEFI ECU and it reads correctly. The 1-wire cluster sensor reads way too high.

JDMClifford: Still stock engine. KA24E

johngriff: The Speedo requires a signal wire only. Neither one registers anything on the Speedo. The speedo also takes 12v and ground, but just to power the digi part of the gauge. Are those temp/voltage ratings for the 2-wire or the 1-wire sensor or both? The Fuel Level schematic in the FSM does show more than the other sensors, but I'm not sure if I'm reading it correctly.

azndoc: All the gauges are Autometer Phantom gauges.

I've mainly been working on getting the speedo working so I may not have tried everything I should on the other two. I'm thinking since you mentioned it's a magnetic sensor that maybe I should try grounding the second speedo wire. Does the sensor actually work like a mini generator? basically using magnetic influence on a coil of sorts to send a brief voltage spike? That would make sense...

I'll get my ohmmeter and check the 1-wire against the 2-wire and see if they're putting off about the same signal. That might at least get be starting on figuring out the water temp sensors.

Fuel level gauge is the one I'm a little clueless on. Here's the part of the Wiring diagram that shows the wires coming from the fuel pump. The other side that goes to the instrument panel doesn't tell us anything. Maybe the Red-Black is the only one I need? i'm just guessing.

[johngriff]

The sensor is grounded via the trans. It has two wires that output the same signal. One is to the instrument cluster, and the other to the ECU.

The defined voltages are for the two wire sensor.

As far as the one wire is concerned, I do not know the voltage workings of the single wire, but it is just a thermistor and for all intensive purposes should be COMPLETELY ignored. It basically works as a switch Off/med/high.

Maybe its about time for me to tackle the Fuel Signal. I want to know the min/max so i can calibrate after market sending units (for fuel cells).

[Blackhat]

Well, if the 2nd wire on the speedo eventually goes to the ecu it must just be so that the ground is guarenteed good. Because I grounded out the 2nd wire and the speedo works now.

I looked a little harder at the Fuel pump wiring and it looks like the green-blue should be the wire that shows fuel level. The red-black looks to be the fuel-low lamp signal. The only problem is I can't seem to make it work. IIRC, Nissans used a 80ohm-10ohm for empty-full signal. Those numbers may not be perfect, but they should be close. That's the gauge type I got for it, and the needle will lift off of empty, but even after filling the tank it shows about 1/8 full. The other wires coming off the fuel pump are the ground (black) and the power for the fuel pump... Those are the only two I'm sure on.

The stock Water temp gauge uses the signal from the one wire. It's basically the same theory as the two wire, except since it's just for a gauge they didn't need the precision of a grounding wire. i would think they would have the same resistances but god knows what the Nissan engineers did there. I haven't gotten out my ohmmetter yet... Mainly because this is the least needed gauge (I can pull water temps off my laptop hooked to my MSEFI).