1995 Chevy 1500 trans/guages problems

Ok I have a 95 chevy 1500 truck. The RPM, Spedo and gear selector work intermediately. when they do not work the trans goes into limp mode (3rd gear). I have found the service bulletin that says that this is caused by lack of power to the shift solenoids. It says to check the voltage at the fuse, by the wiring diagram the hot wire is from the ignition switch and the two out puts go to the trans and the instrument panel. with the instrument panel removed I get 12V to all locations, with it installed I get 5V at the fuse and from the output wire from the ignition switch. The message says the likely problem is the ignition switch. I was also told the common ground could be bad. I don't know about the ground idea though as the rest of the gauges and all other systems work fine. Could this be the ignition switch? 130.00 don't want to make a mistake if it could be the instrument cluster. Thanks for any help You have 12 volts on both red wires at the ignition switch connector? If you are only getting 5 volts from the ignition switch on the pink wire or white wire, something is wrong. With the ignition switch plugged in and ignition turned on take one lead on your meter and back probe the ignition switch connector on the pink wire pin C5. Then take the other lead and connect it to red wire on pin D5. The voltage drop shouldn't be more than .1 volts DC. If it is, time to replace the switch. so I need to test voltage at both points and look for a drop?

Also the white wire has 12 volts until the instrument cluster is plugged in then it drops to 5V

I did not check any other wires on the ignition switch

Here is the message I was going off of

Malfunction Indicator Lamp (MIL) On, Transmission Stuck in Second or Third Gear, Instrument Cluster Inoperative (Verify and Repair Source of Voltage Loss In Transmission Solenoid Power Supply Circuit) TECHNICAL SERVICE BULLETIN Reference Number(s): 01-07-30-002E, Date of Issue: September 23, 2005 Affected Model(s): 2006 and Prior GM Passenger Cars and Light Duty Trucks; 2005-2006 HUMMER H2; 2006 HUMMER H3; 2005-2006 Saab 9-7X; with 4L60-E, 4L65-E, 4L80-E or 4L85-E Automatic Transmission (RPOs M30, M32, M33, MT1, MN8) Supercedes: This bulletin is being revised to update model years, add additional models and add additional diagnostic information. Please discard Corporate Bulletin Number 01-07- 30-002D (Section 07 -- Transmission/Transaxle). Related Ref Number(s): 01-07-30-002A, 01-07-30-002B, 01-07-30-002C, 01-07-30-002D, 01-07- 30-002E ARTICLE BEGINNING CONDITION Some customers may comment on one or more of the following conditions: The Malfunction Indicator Lamp (MIL) is ON. • The transmission is defaulted to second gear (4L80/85-E). • The transmission is defaulted to third gear (4L60/65-E). • The instrument cluster is inoperative. • Upon investigation, one or all of the diagnostic trouble codes (DTCs) P0740, P0753, P0758, P0785, P0787, P0973, P0976, P1860, P2761, P2764 and P2769 may be set depending on the vehicle. CAUSE The most likely cause of this condition may be a loss of voltage to the transmission solenoid power supply circuit. This condition may also be the result of an incorrect installation of an aftermarket electronic device such as a remote starter or alarm system. CORRECTION IMPORTANT: If the vehicle is equipped with an aftermarket electronic device and the DTCs are being set when the device is being used, verify that the appropriate fuse is being supplied battery voltage during operation. If voltage is not present at this fuse, these DTCs will be set due to lack of voltage at the solenoids. This condition is most likely to occur with an incorrectly installed remote starting system. If this is the case, refer the customer to the installer of the system for corrections. ANY REPAIRS DUE TO AFTERMARKET INSTALLATION OF ACCESSORIES IS A NON-WARRANTABLE ITEM. With the ignition switch
in the RUN position, test for battery voltage at the circuit fuse in the transmission solenoid power supply circuit. Refer to the appropriate SI Document for the transmission solenoid power supply circuit information. 1. If battery voltage is present at the fuse, inspect the ignition voltage circuit between the fuse and the transmission for possible opens. 2. If battery voltage is not present at the fuse, test for continuity between the fuse and the ignition switch. If NO continuity is between the fuse and the ignition switch, repair the open in that circuit. 3. If you have continuity between the fuse and the ignition switch, the most likely cause is the ignition switch. Replace the ignition switch using the appropriate Ignition Switch Replacement procedure in SI. Refer to group number 2.188 of the parts catalog for part description and usage of the ignition switch. 4. WARRANTY INFORMATION (EXCLUDING SAAB U.S. MODELS) For vehicles repaired under warranty, use: Warranty Information (excluding Saab U.S. Models) Labor Operation Description Labor Time N6630 Wiring and/or Connector, Transmission - Repair Use published labor operation time WARRANTY INFORMATION (SAAB U.S. MODELS) For vehicles repaired under warranty, use: Warranty Information (Saab U.S. Models) Labor Operation Description Failed Object Fault/Reason Code Location Code Warranty Type Repair/Action Code Labor Time 3711401 Replace part, Adj., Wiring Harness, A/T Incl. diagnosis time 2005 37114 67 0 01 05 Use published labor The white wire feeds the transmission solenoids. The pink wire feeds the cluster fuse and other engine fuses. The white and pink wires coming off the switch both get there power from the red wire on PIN D5. There is another red wire on PIN D2 and that feeds another side of the switch. Faulty ignition switches were a common problem, but it is best not to guess and check to see if that is the actual problem by doing some electrical diagnosis.

What you would be doing by putting one lead on one side of the switch and the other lead on the other side of the switch is measuring the voltage that is dropping through the switch. If there is resistance in a circuit, there is going to be voltage dropping across it. The circuit has to be powered up to measure a voltage drop.

So if you stick your one lead on the white wire pin C1 and the other lead on the red wire pin D5 and you have over .1 VDC, there is excessive resistance in the ignition switch. The voltage may have dropped even more because voltage drops are proportional to the amount of current running through the circuit. When you connect your cluster up, there will be more current running through the circuit and switch. Ohm law applies E=I*R. So, if you have high resistance and more current is added, the voltage drop is going to be higher.

You can measure voltage drop in any part of an electrical circuit to see if there is excessive resistance. You can measure across connectors, switches, wiring, and even loads. Voltage drop testing is extremely helpful in determining if you have battery cable or connection problems in the starting circuit. The main thing is the circuit has to be operating and everything has to be connected while you make your measurements.

ignition switch did the trick Good deal and thanks for letting us know the outcome. Car Repair Talk's forum.