I need a good GPI board for a 88 K75. The one I have is causing the neutral light to stay on constantly and there is no LCD indication at all.

Thanks,
Andy

If the neutral light is staying on constantly, that would suggest that the GPI switch on the back of the transmission is your first issue. The seal cracks up with age and lets water and crud in. 

They can often be carefully dismantled, cleaned, re-sealed and refitted. Careful not to lose small bits and springs. 

Bad news is you have to remove the swing arm to get at it. An opportunity to lubricate the drive shaft splines while you’re at it. 

Bill

Bill, thats what I thought too. So I pulled the swing arm to do a spline lube and removed the switch took ot apart and cleaned and checked it out with a ohm meter. Checked out ok. Wiring up to it is good. So I pulled the cluster and found some burnt resistors .

On my K75 the neutral light stays on constantly and there is no indication on the LCD at all. I took the GPI switch off when I lubed the splines and took it apart, cleaned it and checked it with an ohmmeter. It checked out ok. So I took the cluster apart and found this:

I think I can repair this if i knew what the value of the resistors. I was hoping for a little help on this one. 
Thanks,
Andy

Resistors are color coded so you can tell by looking at the stripes on them how many ohms each one is.

If you search either here on K100-forum or over on Motobrick, you'll find that I've posted many of the schematics for the OEM boards found in the instrument cluster including the GPI board:

https://www.k100-forum.com/t13127-reference-bmw-instrument-cluster-schematics
http://www.motobrick.com/index.php/topic,10566.0.html

If you look at the board, each component is marked on the silkscreen layer. The resistor that has overheated on your board is R10, a 20 Ohm, 1/4 Watt 5% resistor.  This is a current limiting resistor for the power supply.  It sits in front of V6, a ITT ZPY15 zener I believe. If R10 overheated, then that's not good news.  It means excess current was drawn from the supply because of a short condition on Vdd.  You've probably you've taken out a few more components on the board, like possibly V6, C2, IC1 and IC2.  It's possible that V6 failed short.  I foresee a great deal of diagnosis in your future.

Thanks for your reply, Robert. I did find your schematic and replaced both resistors and the diode. I had to "borrow" the components from my son's Radio Shack project thing, but so far it works-although I don't know for how long . Before it wouldn't respond even after I unplugged the trans. switch. Now the neutral light will go off when unplugged and the LCD readout is working, but I think the trans switch is bad. It will light the neutral light in 1st and 2nd and the LCD shows something like a figure 8. In 3rd it reads correct. 4th is back to figure 8, but no light. 5th is correct. I took the switch apart prior and cleaned and rang it out. Seemed ok.

Check the springs in the sensor. I had one go bad, which causes it to read the wrong gear.

Right now, your testing in inconclusive. Your best bet at the moment is to bench test the GPI board. You apparently have the board away from the bike and out of the instrument cluster. Good opportunity to try it.

Use an external power supply to feed 12V DC power to the board. Pin 31 is ground and pin 15 is power. Use jumpers on pins A, B and C to simulate the transmission switch. You'll be bringing them to ground potential in various combinations to simulate different gears. Finally put a 12V lamp or use a volt meter to measure the output on pin LEERL. It should be normally 0V but go to 12V when the ABC inputs are all grounded. The display will indicate the gear number.

Apply different combinations of grounds to pins A, B and C in sequential binary fashion (eg. 001, 010, 011, 100, etc.). See what the display shows. Gear 6 and 7 (eg. inputs 110 and 111) will produce a blank display.

Tell us what the results are.