Temp gauge, AC/Heat fan, Speedometer

[Seuss]

I have a few more issues I'm trying to figure out on my '89 SC, since I got it back on the road. Hopefully someone can point me in the right direction to diagnose and repair these:

1. Temp gauge doesn't seem to work at all. The needle is buried on the left side. It doesn't seem to run hot though.

2. The AC/Heater switch only works in the 4th (highest) position. The other 3 do nothing.

3. The speedometer is erratic. It shows anywhere from about 15MPH slow to about 15 MPH fast and seems to vary between those.

I think these are all I have left to address to have the car fully functioning again. The shocks really need to be replaced, but not sure if we have a direct replacement alternative available now? I replaced the moonroof motor, fixed a leak in the wiper fluid reservoir, rebuilt both window motors, and reglued the moonroof gasket. Making progress!

 

[DOUG H]

Sounds like you have made a lot of progress! Congrat's.

So temp gauge is stuck on cold (left side)? that indicates a open circuit- sender is located at t/stat housing-single term, push on.
Could just be a bad connection there or bad sender. If you ground that wire for a few seconds while someone watchs gauge, it should start to rise.
If it does, is a bad sender or connection. If not, broken wire between there & gauge.

Blower motor only on high is a bad resister 90% of the time. 4 or 5 wire connector in blower housing above pass feet.

Not sure about speedo issue? I know on some other cars I've had (not S/C/ XR-7) if the trans output seal leaked dirt/debries built up on sensor &/or the signal wheel on output shaft & made it erratic. See what others on here think.

 

[Seuss]

Thanks! Hopefully I can dig into it again this weekend. If the blower issue is the resister, does the whole module need to be replaced, or can I just replace the resister?

 

[DOUG H]

Just the resistor, I don't think auto temp was offered in 89? They're not very expensive if my memory serves me correctly.

 

[KMT]

...does the whole module need to be replaced, or can I just replace the resister?

The resistor _pack_ is the service component:

https://www.amazon.com/Dorman-973-404-Blower-Resistor-Harness/dp/B003YLIIAQ/ref=asc_df_B003YLIIAQ/?tag=hyprod-20&linkCode=df0&hvadid=312540934012&hvpos=&hvnetw=g&hvrand=6371153168490161164&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9032937&hvtargid=pla-575010823612&psc=1

 

[KMT]

Dorman 973-060 HVAC Blower Motor Resistor Compatible with Select Ford/Lincoln/Mercury Models - should be the correct part. Don't assume the first link I posted is correct.

 

[Seuss]

Thanks! Ordering it now.

 

[Seuss]

Well, the AC/Heat fan issue is now resolved thanks to the help here! I guess this needed to be replaced. 1 spring was broken/rusted off. Half of the white retaining clip broke off removing the old piece, but it seems to be snug enough with the other side still holding it. Rain started, so I will have to get back to the speedometer and temp gauge next time. This was an easy fix that I made more difficult, but I'm no mechanic, just a guy trying to save a few bucks

 

[Seuss]

Temp gauge fixed, 1 more issue down. It was the Coolant Temp Sender for the temperature gauge. Easy fix there. Now to tackle the speedometer and AC, which also quit working.