My temp gauge sender finally rotted away and yesterday I replaed it with the gauge sensor TS168 and replacement plug S649. I cut and spliced the wires one at a time to hopefully insure I didn't reverse them. Gauge now does not respond and I have a ever so slighty glowing idiot light on in the instrument cluster. So, did I reverse the wires therefore causing the idiot light to confirm I am truely an idiot? Thanks in advance.
1 pin has some Ω to the case threaded into the engine. That's the gauge pin. (Doesn't matter actual Ω measured.) other has nothing because thermal switch that's Open. that's the light pin.
GM FSM and other docs show a wiring problem and cause gauge slamming. GM never fix this. Not even a TSB covering this except maybe saying is normal.... Not. Isn't a "Safety" problems so didn't involved NHTSA recall.
So a Big problem is are several ways to "fix" gauge slamming starting the engine and can't trust GM doc's. 1. only make a change inside of car to the dash cutting/changing wire to I-switch on S-column. 2. switch wires on dash plug and at Sender. 3. switch wires on dash plug and C500.
to test light/gauge... ground the engine end of the wires. Light wire to ground = Light On Gauge to Ground = "Pegged" cold. To Nothing then gauge peg to above high i think.
[This message has been edited by theogre (edited 04-16-2023).]
My guess is a bad sending unit. Simple test to see if it's your wiring: (tho I highly doubt it) unplug it and use two test wires to cross the connections.
My guess is a bad sending unit. Simple test to see if it's your wiring: (tho I highly doubt it)
ALL Fieros came from the factory with incorrect wiring. Even if this specific issue isn't what's causing the problem as described, correcting the wiring issue can only help.
The dim glow on the HOT lamp is likely due to the wires being reversed, as is the gage not responding.
The HOT lamp side would be an open circuit connected to the gage, and the variable resistance circuit is allowing enough of a ground to cause your HOT lamp to glow.
[This message has been edited by olejoedad (edited 04-17-2023).]
I'm refurbishing my '88 GT and the incorrect GM Coolant Temperature Gauge wiring was on my 'fix list'!
I didn't save the link of the infamous "pegging" gauge problem/fix, but I saved a 'word' copy......
From the "Coolant Temperature Gauge Fix - TROUBLESHOOTING" section:
"If your temp gauge doesn't read correctly or the temp warning light doesn't function when you turn the ignition switch to the "Bulb Test" position, the first step is to test the sensor wiring."
"Pull the plug off the sensor and ground either of the two sensor wires to the engine (when the ignition switch is ON). This should cause either the temp warning light to come on or the temp gauge to peg. If this does not happen, then something is amiss in the wiring between the sensor and instrument panel."
"If you get the correct reaction when grounding the sensor wires at the engine but not when the wires are connected to the sensor, either the wiring in the sensor plug is bad or the sensor itself is bad."
"With good wiring and good battery voltage the gauge should peg when the sensor wire is grounded."
And yes, the Standard Ignition TS-168 sensor is also GM 25036809 sensor (coolant temperature gauge and warning switch) which is on the cylinder head near cylinder #5 just below the ignition coil on the V6.
I swapped the two wires on the sensor and the two wires at the instrument cluster so the 'Bulb Test' position applies 12 volts to the Coolant Temperature Warning Light and the Coolant Temperature Gauge works normally without "pegging" when the engine is started which is Awesome!
If you don't find the link in the internet, maybe I can send a copy if you want it, VN
OK the update, but first, thanks again to all. It appears that in a senior moment and dispite my 'fool proof' wire marking I did indeed cross the wires when I installed the pigtail onto the sensor. Switched the wires and all is as it should be.
OK the update, but first, thanks again to all. It appears that in a senior moment and dispite my 'fool proof' wire marking I did indeed cross the wires when I installed the pigtail onto the sensor. Switched the wires and all is as it should be.
except - to actually "fix" the wiring issue, you do have to swap those two wires. But, in addition, there are two wires to swap in the dash display, also.
to this day, it's still one of the most satisfying repairs I've done to my Fiero. IDK, I just get a kick out of the temp lamp illuminating properly for the first time ever.
except - to actually "fix" the wiring issue, you do have to swap those two wires. But, in addition, there are two wires to swap in the dash display, also.
to this day, it's still one of the most satisfying repairs I've done to my Fiero. IDK, I just get a kick out of the temp lamp illuminating properly for the first time ever.
Another method, perhaps simpler, is to remove the ground path to the ignition switch by disconnecting the two small diameter light green wires from the ignition switch. They go to the 'G' terminal on the ignition switch and can easily be removed from the ignition switch connector. Insulate the contact that you remove from the plug.
This 'fix' will prevent the gage from pegging, but not enable the HOT lamp during BULB CHECK.
The HOT lamp will still function in an overheat situation.
Another method, perhaps simpler, is to remove the ground path to the ignition switch by disconnecting the two small diameter light green wires from the ignition switch. They go to the 'G' terminal on the ignition switch and can easily be removed from the ignition switch connector. Insulate the contact that you remove from the plug.
This 'fix' will prevent the gage from pegging, but not enable the HOT lamp during BULB CHECK.
The HOT lamp will still function in an overheat situation.
it's pretty easy to swap the four wires - two under the dash gauges, two in the engine bay. I had it done in about half an hour. I've done it on two now and would definitely do it on any I own in the future.
