Can’t get codes.

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Mar 4, 2025 | 12:04 PM

Slow50

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2nd Gear

Joined: Mar 2025

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Can’t get codes.

Hello, thank you for any help. I just purchased a 1990 F150 5.0. The top end of the motor was taken apart. I put it back together and got it running. The truck was blowing terrible black smoke. I pulled the computer and wound up having to have it rebuilt. So the truck is running very good, but it has a slight tremble. The check engine light does not work. I tried to pull the codes through the test port using a multimeter, but I can’t get anything. I cut back on the harness and I did a continuity test on all the lines and it’s not showing any brakes in the lines. I checked the grounds to the harness and they’re good as well. The multifunction switch has to be replaced, the brake lights were not working so right now it’s disconnected, but I was having this problem prior to me taking the column apart. Does the test port wires also run through the multifunction switch. Thank you for any help. Sorry for the long story.

Mar 4, 2025 | 02:27 PM

jas88

Lead Driver

Joined: Feb 2002

Posts: 7,966

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From: Greater Austin, Texas

I recommend you get the CEL working and then take it from there.

Mar 5, 2025 | 08:18 AM

manicmechanic007

Hotshot

Joined: Jul 2020

Posts: 10,533

Likes: 2,661

From: Near Salt Lake City

+1 for that
and
There is a diagnostic flowchart with procedures for "no codes outputted" and bulb diagnosis in the service manual and the PCED
On your multi function switch, make sure the emergency flasher button is off and switch the flashers from the emergency to T/S and see what happens
Plan on replacing it and search all over for a Ford one