Greetings All,

Long-time forum member here, but in the 80-86 F-series section. This is my first foray here.

I'm trying to help my son with his '99 Mountainer 5.0. He lives about an hour away. Troubleshooting so far is a bit maddening via phone and text. The vehicle is not driven much, maybe a couple thousand miles per year at most. Some critter chewed a little bit of wiring under the hood. The damage was not too extensive, mostly at the coolant temperature sensor, and has since been repaired. He was getting a code related to the coolant temp sensor (Sorry, I do not have the exact code) but that has not returned. He does have a basic scanner and says the ECT signal to the computer appears to be normal now.

The problem is the temperature gauge on the dash is erratic, sometimes showing much hotter than normal. From what I understand, the erratic behavior is too quick to be an actual overheat. He's going to verify this with an IR thermometer but am waiting to hear back. In the meantime, can anybody please direct me to some wiring diagrams? I'm under the impression this engine has two coolant temperature senders. One feeds the computer, and a second sensor feeds the gauge. Is that correct? Or am I in left field? If there are two sensors, can somebody please help confirm which one feeds the gauge?

My son send me this video showing what appears to be the separate sensor for the gauge:



The guy then tears apart his dash and replaces the gauge. From my experience, I'd much rather gamble on the sender first, which is far more likely to act up. Even if the resistance checks fine at certain temperatures, I've had a couple misbehave only in portions of their range.

Thanks for any help you can offer.

 

I have the factory Ford wiring diagrams for the 1999 model year. If you send me a Private Message with the request and an e-mail address to send the PDF (or JPEG, whichever you prefer) diagrams to, I should be able to get those to you this evening.

-Rod

 

Please forgive the slow reply on my part. It may be a while before I can report back with the resolution. This is my son's vehicle so am dealing with it from a distance. He drives it very infrequently so it's on the back back burner for him.

Per the wiring diagrams so graciously supplied above, I was able to confirm the dash gauge is driven by a separate sender than the one feeding the computer. My son was also able to confirm the engine is not running hot, using an infrared thermometer. So now I hurry up and wait for him to replace the appropriate sender and report back.

 

Thank you for the update. I'm glad to hear that the engine has not been running as hot as it's been reporting! That's good news.

-Rod

 

The DATA for the ECT is availably as a PID reporting to a scanner via the DLC