Oil Pressure & Water temperature Gauge

[Bartman]

I've removed my dash to install a Vintage Air System and I'm currently in the process of reinstalling it. While I was at it, I took apart my gauges and installed Speed hut Electro-Luminescent gauge faces. The good part is that I actually got my clock to work now (using info from another thread), the bad part is the Oil Pressure and Water Temperature gauge doesn't.

 

I tried grounding the wires that connect to the sending units with no response from the gauge needles (I read that this should cause the needles to move). I used a test light and it lights up when I do this with the key turned on. Either there's a connection that I missed when I reinstalled or there's a problem with the gauge. How can I test the gauge or the wires that connect to the gauge (can I just provide a power and ground and expect to see the needle move)?

[Bartman]

I disconnected the wire at the sender and grounded it with my test light while suppying power to the corresponding wire at the gauge. This made the light on the test light turn on. So I figured the gauge is wired up correctly and the gauge itself was bad. I found another gauge on eBay for $15 including shipping and hooked it up right away (tried to buy one from a fellow HybridZ member but he wanted $100 plus shipping ). Both water temperature and oil pressure are working perfectly now.

 

I guess the morale is be careful if you take your gauges apart.

[Guest 73LT1Z]

Hey Bart-

I'm running into a similar issue. I finally fired my LT1 this week & all gauges work EXCEPT the oil pressure (you'll be glad to know the fan belt system seems to work). I checked the sender to block for continuity and it was loose- tightened it & now the OP gauge goes all the way to the right with the key on and stays there while the motor is running, then back to the left with the key off. If I pull the sender wire, the needle does not move at all. The sender is a new Datsun item, so I'm thinking this is not the problem. I also took the wiring apart & it has no shorts back to the dash connector. I have the sender wired to the LT1 brown oil pressure sender wire & then this wire goes directly to the Datsun yellow/black oil pressure sender wire via a 3 terminal connector (water temp on there the same way & it works OK).

 

As far as I can tell, I may have damaged the gauge when I first powered it up since the sender was not connected tightly, but I'd think it would recover from this once properly connected. I'd be interested in seeing if there is any way to repair the gauge- I'm not looking forward to pulling the dash (again) so I want to get my ducks in a row before doing so. I do have another one from a 280 (wrong needle color) & will wire it up in the engine bay to see if the gauge is the problem.

[Guest 73LT1Z]

I Googled the topic 280Z oil pressure gauge repair and found this semi-related article dealing with Datsun 510s:

 

Temperature and Fuel Gauge Servicing

 

Article by Nestor Moya

 

 

Do your temperature and fuel gauge not work? Or do the readings fluctuate? A faulty (dirty and/or worn contact points) voltage regulator in the gauge may be the cause of erratic readings or none at all. The voltage regulator is located in the instrument cluster, specifically in the temp/fuel gauge sub-assembly, and directs power to both gauges. So if it malfunctions, it will affect both gauges at once (see Figure 3). The same source from the ignition switch provides power to the voltage regulator and the idiot lights. So if the idiot lights work but both gauges don’t, it’s a sure bet that the culprit is the voltage regulator.

 

Finding and repairing the Voltage Regulator

 

 

Remove the wiper and light-switch knobs (push in and turn 1/4 counter-clockwise).

Disconnect the speedometer cable.

Remove the instrument cluster panel (7 screws).

Remove the four screws that secure the instrument cluster and tip it forward to gain access to its backside.

Disconnect the main electrical plug and any other electrical connections for tachometer, etc.

Pull out the complete instrument cluster.

Remove the temp/fuel gauge assembly by removing the three outermost screws (Figure 1).

Carefully clean the contact points on the assembly and the main circuit board. (I used 600 grit wet/dry sandpaper).

Test Operation of Both Gauges

 

There are three circuit board contacts on the temp/fuel gauge assembly. One is the power supply to the voltage regulator, while the other two are grounds for each gauge. (See figure 2) With a 12 volt positive lead connected to the voltage regulator and a negative lead connected alternately to the temperature and the fuel gauge grounds, each gauge should read full scale. Assemble in reverse order of removal.

 

(There were no figures available as mentioned in the article).

[Guest 73LT1Z]

Hooked up the other gauge & got the same result. Hooked OP gauge to temp sender in head & it didn't move. Looked at the OP sender- it looks a lot like the GM OP sender on my Corvair (small & has a funky wrench fitting)! All of the Datsun senders I've seen are large & round. I figure 1 of 3 things happened:

1) Received wrong sender

2) Ordered wrong sender (too many things going on at once)

3) Failed to change LT1 sender (unlikely, as sender looks new)

 

At any rate, from the looks of things, if I get a genuine/proper OP sender, this should fix my gauge problems & let me keep the dash in place .

 

EDIT

It was both 1 & 2! Went to http://www.rockauto.com and saw the sender they sell for the 1975 280Z is this one:

 

which is what I ordered & received. I think I needed this one:

 

It was listed in the same section (1975 280Z electrical- switch & relay- oil pressure switch). 280 gurus, perhaps the small one is for an idiot light or fuel pump cutoff & the large round one is for the gauge? I don't think my car had an idiot light for OP, so the fuel pump cutoff makes sense since this was the first year of FI for the 280.

[Bartman]

Looks like you worked out your problem, sorry I wasn't of any help. Hopefully the correct sender will resolve everything.

[Guest 73LT1Z]

You've been plenty of help in the AC arena alone. Hope to complete/win that battle soon, a few other bugs to work out but it was nice to have the motor start when I turned the key.