Sounds like your PCB is fried.
Here is some info on "matching" the PCB to the GPC.
The spares procurement for EESS has led to another change which I will commonly refer to as the One Piece Design. Because of the different configurations, we have established a generic NSN for EESS procurement purposes. The NSN is 6110-01-491-2158.
There will be three NSNs related to this generic NSN. They are as follows:
A. 6110-01-463-9260 - 2 piece design manufactured by KDS. This configuration contains a black control box with yellow label and a temperature sensor with a yellow band. The temp sensor gets installed in the water crossover pipe.
B. 6110-01-491-2142 - 1 piece design manufactured by KDS. This configuration contains a black control box with a bright green label. There is no longer a separate temperature sensor required with this configuration. It will not make a difference whether the glow plug controller (2920-01-175-7214) or the temp sensor (2920-01-469-6903) is installed in the water cross over pipe. The pin to this lead is dead.
C. 6110-01-491-2152 - 1 piece design manufactured by Signal and Systems, Inc. (SSI). This configuration contains a black control box and there is no separate controller or temp sensor. It will not make a difference whether the glow plug controller (2920-01-175-7214) or the temp sensor (2920-01-469-6903) is installed in the water cross over pipe. The pin to this lead is dead.
* Any of the above NSNs can be ordered, you will get which ever is in stock.
* There are NO Safety Issues related to these boxes/NSNs.
* You should no longer get a blinking/flashing wait to start light when using the one piece design. The box should no longer go into default mode.
* You no longer will need to troubleshoot the temp sensor/controller if you have the one piece design installed. However, be sure to keep the temp sensor/controller installed and connected.
* Still need to make sure glow plugs are in good working condition - no need to automatically replace them, just check them.
* Ensure that your connections to the body and engine side a good and tight.
* The voltmeter will still fluctuate during after-glow activity.
Bottom line - the one-piece design is the same as two piece design except for the temperature sensor.
If you suspect a problem with the starting system (control box):
1. Check batteries
2. Check all 8 glow plugs
3. If Wait to Start Light does not come on, but you had voltage gauge activity - attempt to start vehicle. If no start, check fuel system.
4. If Wait To Start Light comes on and you have voltage gauge activity, and still get a no start - your control box should be functioning, problem may be fuel related - check fuel system.
5. If no Wait to Start Light, no glow plug activity and no vehicle start; and all 8 glow plugs are good, wait to start light is good and connections at the body and engine side are good and tight, batteries are good - replace control box.