OrangeBird

iTrader: (1)

I recently decided I no longer wanted my temperature gauge to peg to max temp every time I turned the key to start . I made this decision after having my original temp gauge get stuck at the max temp position , causing me to have to replace the gauge . So I checked the schematic and it indicated one small dark green wire coming from the ignition switch was the wire responsible so I went under the dash to cut the offending wire , but was instead confronted with TWO small dark green wires connected to same terminal of the ign switch ! Now looking at the wiring diagram it clearly shows the tie point for the two wires as being at the gauge head itself with one wire running to the ign switch and the other to the engine mounted sensor . Not so in actual practice , the two wires tie point is indeed at the switch . No biggie , I cut both wires from the ign switch , soldered and shrink wrapped them together , and my gauge works fine without the gauge killing peg to max on each startup . That was mistake #1 in the diagram . Mistake #2 is that they have the switch drawn as grounding the sensor wire(s) when in the "run" position , rather than in the "bulb test/start" position as it's supposed to be . I just can't see how it could be healthy for a gauge that's supposed to see a minimum resistance of 55 ohms at full scale being subjected to 0 ohms at each startup , without eventually destroying the gauge (as my original one was) by being pegged SO hard as to be able to actually hear the gauge slam on the max temp reading at each startup .....

Chalk this one up to , even the FSM can have bad info , "As wired" looking one Hell of a lot different from "As drawn" .

OrangeBird

iTrader: (1)

Here is the actual "as wired" diagram , please excuse my lacking photo editing skills but I believe this picture to be a perfect representation of how the circuit is actually wired

OrangeBird

iTrader: (1)

And the finished product ....

scooter

iTrader: (11)

Seeing the sweep lets you know the gauge is actually still working though

OrangeBird

iTrader: (1)

Hi Scooter ,

I absolutely 100% agree with you , so much so that I had considered putting a 50 ohm resistor in series with the "bulb test" contact of the ignition switch to soften the SLAM as the needle pegs with each start . Laziness , and the fact that I'm one of those who glances at the gauges very often , means that by 5 or 10 minutes of running if I see no gauge movement I'll be checking the gauge by unplugging the sensor and putting a resistor between it and ground to check for needle movement . After having one gauge get stuck I just couldn't let the replacement gauge die the same pegged death .

Drew

iTrader: (58)

Hmm, but if the gauge was worn enough to not pass the destructive self test, was not the gauge already kaput?

Never had a problem with the Firebird clusters, but the pre-1990 Camaro clusters are pure garbage. Added stops to the gauge face on the Iroc because it'd thrust the needle so hard it'd stick high. After putting a stop on the high side, it'd hit the stop so violently it'd recoil back and stick low. Now with a stop at each end it just hammers around like a pinball flipper until the bulb test is over.

W.E.G.

I too was plagued with the spastic-and-gets-stuck needle when turning to key-on.

I used two small tacks from a kit for hanging small frames. Black-Sharpied the nails after the glue dried.

I used Q-Bond super glue to glue the nails to the face of the gauge to limit travel to just a wee bit more than the marked min/max ranges. After a week or so, seems to be holding solid. Now, if only the gauge wouldn’t read nearly 260, while the upper radiator hose laser-measures 210.

OrangeBird

iTrader: (1)

To Drew , Yes indeed my friend the gauge not surviving the peg to max test was proof positive that the gauge itself had failed . But in my thoughts , it was a kind of "which came first , the chicken or the egg" conundrum , did the gauge die a "natural" death , or was it deliberately murdered by it's lifetime of being pegged on each startup ? It was my opinion that had the gauge not been pegged so hard at each startup maybe it would have lived on , as my original oil gauge has , since it's not pegged with each turn of the key . In hindsight had I desired to keep the gauge test function intact a 50 ohm resistor in series with the bulb test contact really would have been the way to go , but , where none of the other gauges peg on startup I made the decision to eliminate that function alltogether and just keep my normal watchful eye on it as the car warms up from each cold start .

To W.E.G. , Installing "stops" was a very good idea to keep the gauge from getting stuck , but the poor gauge's electrical movement is still being subjected to that 0 ohm slam , when in it's normal running operation it is never subjected to less than around 50 ohms . I can see where if the car always starts easily the 0 ohm slam will be very brief indeed , but what of those occasional cold mornings when the engine needs to be cranked over a bit longer to get it to fire up , with all those additional seconds of the 0 ohm slam heating the Hell outta the gauges deflection coils ?

The thing to me is , as an electronics hobbyist the first golden rule of meters is to never subject them to such overload as to cause the needle to peg like that , indeed over the years I've seen countless meters (like the venerable "Simpson 260") destroyed by folks measuring too high a voltage or current with them , causing the pegged meter to burn out it's delicate movement coils . While I realize our car's gauges are far more "ruggedized" that the delicate movement of such a sensitive instrument as the Simpson , I now have seen at least one temp gauge (my original one) destroyed by what in my belief is the excessive strain of the startup peg .

I truly appreciate all the responses to this thread , I had hoped to have folks present the different talking points and viewpoints you all have presented , to give me a sounding board to solidify my thoughts on this issue . In retrospect I think for anyone else considering trying to save their temp gauge I'd recommend the 50 ohm resistor if the gauge test functionality is desired to be preserved . Oh , and , this thread serves proof that even the FSM can have mistaken info , as proven by my above corrections to the original wiring diagram drawing .