Fixed One Electrical Issue and Got Another

[divemaster5734]

I recently posted about the engine wiring harness in my C350.
The cold start high idle didn't work.
After some investigation I discovered severely corroded wires and connectors.
I took the engine harness out, eliminated the glow plug wiring at the back, and relocated it to the front crossmember next to the radiator.
I also discovered other damaged wires, and spliced in fresh sections.
The cold start system worked when reinstalled, but the tach stopped, and the check engine light stayed on.
I know there's some issues with the dash, but don't think those issues caused the new ones.
There's two engine harnesses, one that serves the charging system, tags the tach at the timing gear, and ends at the AC connector.
I never touched it. Just realized I may have accidentally dislodged it while playing around with the other harness, and will check tomorrow.
I'm not sure where the engine light comes from though, and that was the reason for my post.

 

[franklin2]

What year are you working on. I know on my 89, the "brake" light will come on when the vacuum switch triggers on low vacuum. And my "engine" light comes on when the temp gauge pegs and it thinks the engine is hot.

 

[franklin2]

Here's a diagram for a 86. It looks much the same as my 89.

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[divemaster5734]

What year are you working on. I know on my 89, the "brake" light will come on when the vacuum switch triggers on low vacuum. And my "engine" light comes on when the temp gauge pegs and it thinks the engine is hot.

'89 F350 Lariat crew cab short box.
Was so focused on the electrical I didn't even think to check the vacuum lines.
I believe I know the exact culprit.