Speedo Gauge Wiring Question

[bonhamsurf]

I'm still attempting to finish the conversion of my dash to LED's and different colors. I've read all the threads and also studied the manual, but can't figure out how to test the dash lights while the entire unit is out. Some of my LED's are upside down, and I want to put a12v battery on the unit while it is outside of the car to do some testing. Does anyone know where on the instrument cluster unit I can put a 12v battery on to test the lights with the unit out? Thanks!

 

[Old Guy]

You have not specified your vehicle year. For the '91 cars, if you go to page 23-123 of the service manual, you will find the numbering designation for the two 30 pin connectors on the back of the instrument cluster. The connector pin numbers are A1-30 and B1-30. If you go to the gauge wiring diagram (starting at page 23-124), you will see that each wire on the periphery of the section of the diagram marked gauge assembly has a designation such as A21. This refers to the pin number on the respective connector. It looks like the gauge illumination is connected between pins B9 and B10.

The cluster changes slightly from year to year so these may not be correct page references for your model year. However, you should be able to find similar diagrams in the service manual for your model year which would give you the appropriate pin numbers.

If the terminations on the back of the cluster are male, be careful applying voltage to the pins as it would be super easy to zap something else if you brush up against one of the other pins

 

[bonhamsurf]

You have not specified your vehicle year. For the '91 cars, if you go to page 23-123 of the service manual, you will find the numbering designation for the two 30 pin connectors on the back of the instrument cluster. The connector pin numbers are A1-30 and B1-30. If you go to the gauge wiring diagram (starting at page 23-124), you will see that each wire on the periphery of the section of the diagram marked gauge assembly has a designation such as A21. This refers to the pin number on the respective connector. It looks like the gauge illumination is connected between pins B9 and B10.

The cluster changes slightly from year to year so these may not be correct page references for your model year. However, you should be able to find similar diagrams in the service manual for your model year which would give you the appropriate pin numbers.

If the terminations on the back of the cluster are male, be careful applying voltage to the pins as it would be super easy to zap something else if you brush up against one of the other pins

THanks for the input. My car is a 1991.
Looking at the diagram per your instructions, I see that on page 23-125 "B9" goes to "FUSE" and "B10" goes to "Dash List brightness Controller" . To make sure I give it power correctly, do I need to hook the positive side of my 12v battery source to BOTH B9 and B10 and ground my negative side?

 

[Old Guy]

THanks for the input. My car is a 1991.
Looking at the diagram per your instructions, I see that on page 23-125 "B9" goes to "FUSE" and "B10" goes to "Dash List brightness Controller" . To make sure I give it power correctly, do I need to hook the positive side of my 12v battery source to BOTH B9 and B10 and ground my negative side?

I just noticed that there is a second set of gauge lights between pins A25 and A24. Pins A25 and B9 got to 'fuse' and as such would normally be connected to +12 volts. Pins A24 and B10 go to the dash light brightness controller. If your LEDs are rated for full 12v, you should be able to connect pins A25 and B9 to the test battery +12v and pins A24 and B10 to the negative terminal (ground) of the battery. This will test the gauge lights only. If you have converted other lights in the cluster to LEDs, then you will have to figure out which pins are connected to those lights.

Just a heads up. In older simpler systems brightness control would be via a simple rheostat. In such a system, the lights are connected to ground through the rheostat. However, nothing is simple on an NSX. I had a quick look at the brightness controller wiring on the NSX and it is not a simple rheostat, so I am not sure exactly how it works. If it uses a pass transistor type regulating device, it may not work very well, or at all with LEDs. Then again, it might work just fine. Just don't be surprised that if you test the lights on the bench with a battery, it works; but, doesn't work in the car, or that the brightness control does not work very well. It will be interesting to hear how this works out.

 

[bonhamsurf]

I just noticed that there is a second set of gauge lights between pins A25 and A24. Pins A25 and B9 got to 'fuse' and as such would normally be connected to +12 volts. Pins A24 and B10 go to the dash light brightness controller. If your LEDs are rated for full 12v, you should be able to connect pins A25 and B9 to the test battery +12v and pins A24 and B10 to the negative terminal (ground) of the battery. This will test the gauge lights only. If you have converted other lights in the cluster to LEDs, then you will have to figure out which pins are connected to those lights.

Just a heads up. In older simpler systems brightness control would be via a simple rheostat. In such a system, the lights are connected to ground through the rheostat. However, nothing is simple on an NSX. I had a quick look at the brightness controller wiring on the NSX and it is not a simple rheostat, so I am not sure exactly how it works. If it uses a pass transistor type regulating device, it may not work very well, or at all with LEDs. Then again, it might work just fine. Just don't be surprised that if you test the lights on the bench with a battery, it works; but, doesn't work in the car, or that the brightness control does not work very well. It will be interesting to hear how this works out.

Thanks again for your continued input on this. Your reference to A25 is a little confusing. You say A25 and B9 go to fuse, but then you say A25 and B10 go to the brightness controller. You then suggest I connect A25 to both the positive and the negative on the test battery, while connecting B9 to the positive and B10 to the negative all the same time?

 

[Old Guy]

Thanks again for your continued input on this. Your reference to A25 is a little confusing. You say A25 and B9 go to fuse, but then you say A25 and B10 go to the brightness controller. You then suggest I connect A25 to both the positive and the negative on the test battery, while connecting B9 to the positive and B10 to the negative all the same time?

I was a little confused by your question, particularly when your quote refers to A24 and B10, not A25 and B10. There were problems with saving edits to the post last night and it took a while before I got the final post corrected. You must have read and responded to the post 'mid correction'. The forum server must have updated the quote after you posted. If you check the final version of the post above, done at 22:18, you will see that I corrected the reference to A24 and B10 as the terminals that connect to the controller. In the original uncorrected post I had typed A25 so I can understand your confusion. So, to be brief, A25 and B9 go to battery +12v, A24 and B10 go to Battery -12v. Again, before you do the test make sure your LEDs are rated for a full 12v.

- - - Updated - - -

One more quick note. LEDs devices are polarity sensitive (it matters which terminal is connected to + and -). A lot of the LEDs for automotive applications (i.e. festoon style bulbs in the NSX ceiling light) will have internal circuitry so that the LED light can be inserted without regard to polarity. If your LEDs are polarity sensitive, you need to make sure that the + terminal is connecting to A25 or B9. If they are not polarity sensitive, then you are good to go.

 

[bonhamsurf]

I was a little confused by your question, particularly when your quote refers to A24 and B10, not A25 and B10. There were problems with saving edits to the post last night and it took a while before I got the final post corrected. You must have read and responded to the post 'mid correction'. The forum server must have updated the quote after you posted. If you check the final version of the post above, done at 22:18, you will see that I corrected the reference to A24 and B10 as the terminals that connect to the controller. In the original uncorrected post I had typed A25 so I can understand your confusion. So, to be brief, A25 and B9 go to battery +12v, A24 and B10 go to Battery -12v. Again, before you do the test make sure your LEDs are rated for a full 12v.

- - - Updated - - -

One more quick note. LEDs devices are polarity sensitive (it matters which terminal is connected to + and -). A lot of the LEDs for automotive applications (i.e. festoon style bulbs in the NSX ceiling light) will have internal circuitry so that the LED light can be inserted without regard to polarity. If your LEDs are polarity sensitive, you need to make sure that the + terminal is connecting to A25 or B9. If they are not polarity sensitive, then you are good to go.

THanks again for your input. I plan to pull my dash out later this week and test per your instructions. I'll keep this thread updated with the results.

 

[bonhamsurf]

I was a little confused by your question, particularly when your quote refers to A24 and B10, not A25 and B10. There were problems with saving edits to the post last night and it took a while before I got the final post corrected. You must have read and responded to the post 'mid correction'. The forum server must have updated the quote after you posted. If you check the final version of the post above, done at 22:18, you will see that I corrected the reference to A24 and B10 as the terminals that connect to the controller. In the original uncorrected post I had typed A25 so I can understand your confusion. So, to be brief, A25 and B9 go to battery +12v, A24 and B10 go to Battery -12v. Again, before you do the test make sure your LEDs are rated for a full 12v.

- - - Updated - - -

One more quick note. LEDs devices are polarity sensitive (it matters which terminal is connected to + and -). A lot of the LEDs for automotive applications (i.e. festoon style bulbs in the NSX ceiling light) will have internal circuitry so that the LED light can be inserted without regard to polarity. If your LEDs are polarity sensitive, you need to make sure that the + terminal is connecting to A25 or B9. If they are not polarity sensitive, then you are good to go.

Ok, so I finally got around to trying this out.
Putting a 12+ to A25 and a 12- to A25 only lights up the 2 overhead, the 2 bulbs that site behind the orange lens at top of the cluster.
Then, putting 12+ to B9 and 12- to B10 only light up light up the odometer.

So, how would you suggest I test all the other lights to ensure they're working before I put it all back to gether. thanks

 

[bonhamsurf]

So I tried various combos of plugs today.
Here's what I found
A25 to 12v+ and A24 to 12v- = Overhead 2 bulbs behind orange plastic film.

B9 to12v- and b10 to 12+ = Tach light one
Reverse this to B9 to 12+ and B10 to12- = Temp light on.

At this point, I decided to plug it back into my car,
in whcih case nothing workied except the TCS, the Right Turn Signal and the Anti-Lock brake light.

Nothing else woud turn on. Very frustrated