Originally Posted by JamesC

I actually only used the insulator as I wasn't too keen on snipping the wiring unnecessarily

Originally Posted by irocz1985

hey, i finally fixed my temp gauge. i cut the dark green wire behind my instrument panel and ran a fresh wire straight from my coolant temp sender to the cut wire. works just like it did in 1985!!! thanks alot for all your knowledge. by pointing me to the instrument panel i was able to locate the wiring, when all this time i was thinking it wired to the ecm.thanks alot chevy86iroc-z!!!!

Originally Posted by irocz1985

hey, i finally fixed my temp gauge. i cut the dark green wire behind my instrument panel and ran a fresh wire straight from my coolant temp sender to the cut wire. works just like it did in 1985!!! thanks alot for all your knowledge. by pointing me to the instrument panel i was able to locate the wiring, when all this time i was thinking it wired to the ecm.thanks alot chevy86iroc-z!!!!

Originally Posted by Dylan Pfeiffer

Hey is this safe to do?

Originally Posted by Ward

They are all single wire - the sensor is a thermistor, meaning that it's resistance changes with temperature. The hotter the temperature, the lower the resistance. The reason it's a single wire, is because it is wired in series with the gauge ground wire. The positive wire to the gauge has 12V ignition switched. As temperature increases, the sender allows more current to ground to the engine block, moving the gauge needle up. It's also why shorting out the sender wire (no resistance) causes the gauge to peg on full hot. Pretty much all temperature gauges work this way, and have for at least the last 50 years.

The CTS, which is used by the ECM to measure temperature, is also a thermistor. However, it has 2 wires, which both go to the ECM. This is so that the ECM can directly measure the resistance across the wires, by sending 5 volts through one wire, and measuring the voltage that comes back. The higher the voltage, the higher the temp.

Originally Posted by QwkTrip

I don't know where this "black wire" ever came up in discussion?

The temp gauge has two circuits with two grounds. One ground is inside the interior of the car. Other ground is the temp sender on the engine. Wires in the gauge circuit are:

1. Pink with Black stripe: +12V power supply from the fuse panel under the dash to the gauge.
2. Black: Ground for the gauge itself. This is grounded to the car somewhere inside the interior, maybe near the steering column.
3. Dark Green: The actual wire that goes to the coolant temp sender on the engine. Only 1 wire is needed to the sender because the sender is electrically grounded by contact to the engine block. In other words, the body of the sender itself is the "ground wire" so you don't need (and won't see) a separate ground wire leaving the sender.

That's it. That's all there is.

As far as how it works... The temp gauge swings up or down based on how much current is passing through it. And the coolant temp sender is basically a variable resistor that changes the amount of current allowed to pass through the gauge dependent on temperature. There is no "signal" or "number" being sent back to the gauge, or any other kind of data processing happening. The gauge is literally just swinging up and down according to how much electrical current is passing through the Dark Green wire to the sender. Get that out of balance and the gauge stops working right.

Originally Posted by sofakingdom

Pegs at start = it's supposed to do that; it mimics the behavior of the warning light is cars equipped with it, as a "bulb check"

Does the gauge read zero normally, and peg when you ground the dark green wire? (with power applied of course; key On)

Originally Posted by sofakingdom

Then it's a problem with the sensor. Either it's bad (not likely, but of course also not impossible), or it's not grounded effectively to the head. Too much teflon tape for example.

Originally Posted by sofakingdom

The sensor should be in the driver's side head, between the #1 & #3 spark plugs. That might have something to do with the issue at hand.

Originally Posted by Jacobmccannell

understood I'll move it and see what happens

Originally Posted by QwkTrip

How is the engine itself grounded to the chassis, and how is the chassis grounded to battery? That's all part of the circuit too.

Paint will insulate too, so make sure things are in contact with bare metal anywhere there is a connection.

Originally Posted by sofakingdom

The battery shouldn't be grounded to the chassis. That's a recipe for disaster.

It should be grounded to the engine, preferably the block itself, or something as close to it as possible. In these cars the factory often put it to one of the accessory brackets.

It's EXTREMELY important however, that the engine and chassis grounds be solidly connected together. The factory used those braid straps between the back of the heads and the firewall for this.

Originally Posted by sofakingdom

No it was NOT.



OK fine. I won't argue with you there. But SOMEONE did.



The BIG wire needs to be WHERE THE HIGHEST CURRENT IS FLOWING. The highest current flow in a car, is the starter motor. This means that the BIG RED wires (batt cable) needs to go from the + batt terminal DIRECTLY to the starter; the starter of course is bolted to the block; the BIG BLACK cable that returns the current to the batt needs to be bolted as close as electrically possible to the starter, which means, the block. If not the block itself, as close as you can get, which the factory's usual method was to use a very short cable and go to a large bracket as close to the batt as it could. I'm guessing that they thought that a short cable bolted to the bracket was electrically superior to a long cable bolted to a casting piece farther away. They're probably not wrong: that'd be pretty eeeeezy data to collect, and I'm sure they did just exactly that.

PUT THE COPPER WHERE THE CURRENT IS. (speaking strictly as a mathematician and physicist for whom those specialties was NOT a marketable skill at the time, so I've been making my living as an electrical/electronic engineer for the last 40 some years)



Well then that's a serious EFFFFF up. The ground from the batt should be hooked to the block, and then there should be a good connection from there to where the most current in the chassis ends up trying to find its way back to the batt which is the firewall which is why the factory connected between the heads (closest readily available point nearest the block which is arbitrarily close to where the neg batt cable goes) and the firewall. The fender isn't even a particularly good place for that secondary bonding connection. Firewall is much better since so many of the car's interior and whatnot electric things attempt to ground themselves to that. The fender is just a piece of random trim hung off in space somewhere somewhat near the CAR proper. The inner fender is PLASTIC, not even a conductor. You have a HACK JOB on your hands.

It's no wonder your car's electrical system is so messed up. Somebody has got in there before you and SODOMIZED it. Without the courtesy of using any Kentucky jelly even, I'm afraid.



OK, so put the sending unit where it belongs (the driver's side head between the #1 & #3 spark plugs) like we keep telling you, and THEN see if it works.

Quit trying to make your CRAPPY RIGGED UP HACKED POS PO HACK JOB work, and PUT THE CAR BACK LIKE IT BELONGS, and go from there. Understand and IMPLEMENT the difference between "fix" (what you're trying to do) and "repair" (make it RIGHT).

Originally Posted by sofakingdom

No it was NOT.



OK fine. I won't argue with you there. But SOMEONE did.



The BIG wire needs to be WHERE THE HIGHEST CURRENT IS FLOWING. The highest current flow in a car, is the starter motor. This means that the BIG RED wires (batt cable) needs to go from the + batt terminal DIRECTLY to the starter; the starter of course is bolted to the block; the BIG BLACK cable that returns the current to the batt needs to be bolted as close as electrically possible to the starter, which means, the block. If not the block itself, as close as you can get, which the factory's usual method was to use a very short cable and go to a large bracket as close to the batt as it could. I'm guessing that they thought that a short cable bolted to the bracket was electrically superior to a long cable bolted to a casting piece farther away. They're probably not wrong: that'd be pretty eeeeezy data to collect, and I'm sure they did just exactly that.

PUT THE COPPER WHERE THE CURRENT IS. (speaking strictly as a mathematician and physicist for whom those specialties was NOT a marketable skill at the time, so I've been making my living as an electrical/electronic engineer for the last 40 some years)



Well then that's a serious EFFFFF up. The ground from the batt should be hooked to the block, and then there should be a good connection from there to where the most current in the chassis ends up trying to find its way back to the batt which is the firewall which is why the factory connected between the heads (closest readily available point nearest the block which is arbitrarily close to where the neg batt cable goes) and the firewall. The fender isn't even a particularly good place for that secondary bonding connection. Firewall is much better since so many of the car's interior and whatnot electric things attempt to ground themselves to that. The fender is just a piece of random trim hung off in space somewhere somewhat near the CAR proper. The inner fender is PLASTIC, not even a conductor. You have a HACK JOB on your hands.

It's no wonder your car's electrical system is so messed up. Somebody has got in there before you and SODOMIZED it. Without the courtesy of using any Kentucky jelly even, I'm afraid.



OK, so put the sending unit where it belongs (the driver's side head between the #1 & #3 spark plugs) like we keep telling you, and THEN see if it works.

Quit trying to make your CRAPPY RIGGED UP HACKED POS PO HACK JOB work, and PUT THE CAR BACK LIKE IT BELONGS, and go from there. Understand and IMPLEMENT the difference between "fix" (what you're trying to do) and "repair" (make it RIGHT).

Originally Posted by Jacobmccannell

Originally Posted by sofakingdom

Nothing about Sir Richard going on here, unless you choose to make it so. LEARN or remain ignorant. Your choice. I can stop helping, if you think that'll get your car fixed faster. Somehow though, I think NOT.

Your BIG black cable needs to go to something as close as possible, electrically, to THE BLOCK. Where does it go?

The little tiny weenie other wire that goes to the fender is ... NOT of any particular significance. About all it's meant to do is, provide a path for headlight and turn signal current.

The important wire is THE BIG ONE. Where does it go? Should go to the block, or something as close as possible to it, electrically. The little wire that you showed all those photos of is ... little. Not our concern here.

But that's a whole other matter on top of your gauge issue. Let's unravel one stoooooopid PO EFFF-UP at a time. How did the gauge work when you put the sending unit in the right place and hooked up the wire to it?

Originally Posted by Jacobmccannell

The big cable goes to the block well hooked to an exhaust manifold bolt

The gauge still pins once key is turned and then I have to manually put it back down to normal range after that once the car is started it does nothing