'90 GT instrument cluster lights + upgrade

I had the exact same problem with my water temp gauge. But no other gauges. I put in a new sensor, replaced the cluster, everything I could think of to no avail. Some say there is a voltage regulator under the dash somewhere that regulates all the voltage going to the insturment cluster, and when it goes bad your exact problems occur. I just bought an Autometer temp and volt gauge w/ full length a pillar and it solved my problems. Good luck! I wanna know the problem also, as I'd like to take out the autometers and just run the stock gauges (even though the water temp gauge sucks). I don't like the gauge look.. Not on this car. It's too stock

Nick

bump

Heres the Fix. It works everytime!!!!!!!!!!!!!!!!!!!!!!!!!!

I like guages I don't have much advise right now so I'm just subscribing

I saw a simuliar type problem in an sn95. It turned out to be I missed a body ground when swaping engines. Not sure if it would be the same here or not.

5.0Droptop said:

Heres the Fix. It works everytime!!!!!!!!!!!!!!!!!!!!!!!!!!

Click to expand...

where would i get that setup?

+1 for the bad ground. We were changing the water pump in my buddys mustang a few years ago. After everything was back in place, there were no leaks, but the guages went ape **** when you turned the headlights on. It took us a while to find the culprit, but sure enough it was a bad ground.

Another vote for a bad/missing ground.

Grounds are important to any electrical system, and especially to
computers.

1.) The main power ground is from engine block to battery: it is
the power ground for the starter & alternator.

2.) The secondary power ground is between the back of the
intake manifold and the driver's side firewall. It is often missing or
loose. It supplies ground for the alternator, A/C compressor
clutch and other electrical accessories such as the gauges.
Any car that has a 3G or high output current alternator needs
a 4 gauge ground wire running from the block to the chassis
ground where the battery pigtail ground connects. The best
place for the block ground is where the battery ground for the
starter bolts down. The 3G has a 130 amp capacity, so you
wire the power side with 4 gauge wire. It stands to reason that the
ground side handles just a much current, so it needs to be 4
gauge too.

The chassis ground and battery pigtail ground go to the bolt being
pointed at in the following photo.

Picture courtesy timewarped1972

3.) The computer has its own dedicated power ground that
comes off the ground pigtail on the battery ground wire. Due to
it's proximity to the battery, it may become corroded by acid
fumes from the battery. It is a black cylinder about 2 1/2" long
by 1" diameter with a black/lt green wire.You'll find it up next to
the starter solenoid where the wire goes into the wiring harness.
The computer's main power ground (the one that comes from
the battery ground wire) uses pins 40 & 60 for all the things it
controls internally.


4.) All the sensors have a common separate ground. This
includes the TPS, ACT, EGE, BAP, & VSS sensors.

5.) The O2 sensor heaters have their own ground (HEGO ground)
coming from the computer. This is different and separate from
the O2 sensor ground. It is in the fuel injector wiring harness and
comes out under the throttle body. It gets connected to a
manifold or head bolt.

6.) The TFI module has 2 grounds: one for the foil shield around
the wires and another for the module itself. The TFI module
ground terminates inside the computer.

7.) The computer takes the shield ground for the TFI module and
runs it from pin 20 to the chassis near the computer.

See http://www.fluke.com/application_notes/automotive/circuit.asp?AGID=1&SID=103#volt
for help troubleshooting voltage drops across grounds

Extra grounds are like the reserve parachute for a sky diver.
If the main one fails, there is always your reserve.

The best plan is to have all the grounds meet at one central spot
and connect together there. That eliminates any voltage drops
from grounds connected at different places. A voltage drop
between the computer ground and the alternator power
ground will effectively reduce the voltage available to the
computer by the amount of the drop.

I have thought about those for a while, but i'm not totally positive it looks right. If you has seen them in person they look like you just sit them in place of the old cluster, the fit didn't look that great. Kind of like they were just mickey'd to get them in.

Here's the link to go to that dash kit:
http://www.florida50.com/CL_87-93.htm

Thanks

Yes, you should have an instrument voltage regulator as part of the printed circuit on the back of the cluster. It makes 5 volts out of 12 for the water temp, oil pressure and gas gages, at least on my 79-82 cars. It can fail, but that kills all 3 gages.

The grounding problem sounds like your most likely cause.

Dude!!!

Same exact identical problem!
I was searching for advice on this same problem- it started last week when I put in an electric fan, so now I'm upgrading to autometer oil and water temp guages so I'll let you know, also I'm gonna add a ground 4 guage I think

68torinogt said:

where would i get that setup?

Click to expand...

www.florida50.com

I also had the same problem with the water gauge. I would turn the lights on and the temp gauge would immediately go up. I just did the 3g swap and added the ground and the temp gauge doesn't move at all when I turn the lights on. I don't know why but it worked.

I have a strange problem as well. As soon as the tach gets power even though the car isn't running the tach jumps to 4grand. Havent had time to deal with it yet, I guess I'll check the grounds first, before I rip off the dash.

The instrument cluster ground is located at the lower front of the driver's side wheel well. I've seen them work loose so you might want to check it out. You might also have a bad ground connection at the back of the cluster.

As for the IVR (Instrument Voltage Regulator) I did some light research a couple of years back and read that the IVR is used on bimetal indicating systems (the Tbird makes extensive use of the IVR). The Mustang (info sourced from an 88 manual) uses magnetic gauges and with the exception of the fuel level gauge does not use the IVR. On a Mustang the IVR (also called the slosh module depending on what page you're looking at) is used to provide a steady 5v pulse to the fuel gauge.