I know I posted about this about September 2018 but I can't find it.

Back then I replaced #4 glow plug but still kept getting SEL with new plug. After changing the glow plug twice I still got P0674. So I determined it was probably the GP Controller. Changed it still same problem. Not so bad when its warm enough they don't cycle so now SEL.

Now recently I started getting P0678. Today I decided to fix it once and for all. Did some research and figured I could figure things out. Pulled #4 get 0.6 ohms on it. Same on #8. Well lets try #2 its working and its the same.

Key off I have 0.9 volts going to all 3 leads when disconnected. Key on 2.4 volts. Start and when plugs cycle 11.4 volts then drops back to 2.4 volts.

Started it with #2 disconnected and got P0672, P0674, and P0678. Cleared again P0672 is gone but P0674 and P0678 keep coming back and setting SEL.
Tomorrow I plan on disconnecting both batteries and grounding positive leads for an hour. Did that after I replaced the GP Controller just hoping it will work this time.

Any other suggestions?