Transmission Problems
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Beginning Member
Joined: Dec 2016
Posts: 16
Ok. So could be by design the voltage is being pulled to ground which is I believe might be by design and would be why you don't see voltage. So let's take that element out. Unplug the Stop Lamp Switch and the plug at the Shift lever for the solenoids. Check the harness side of the shift lever plug. Nothing should be pulled to ground then. Probe that LT GRN/BLK wire on the harness side of the solenoid plug to see if you get voltage. Also probe the same color wire on the harness side of the Stop Lamp switch for voltage. You should see voltage on both wires. At least then we will know for sure that everything is good up to those two plugs.
But have both plugs unplugged at the same time (Stop Lamp Switch and Shift Lever plug).
But have both plugs unplugged at the same time (Stop Lamp Switch and Shift Lever plug).
Super Member
Joined: Nov 2011
Posts: 1,139
From: Pennsylvania
Also should have mentioned that you want the plug at the PNP connected for the above check. Only the stop lamp switch plug and the plug at the shift lever disconnected.
If you don't get any power at those two LT GRN/BLK wires, I would think the problem resides in your PNP switch. If you do get power, it is either a mechanical problem with the shifter/tranny or an electrical problem after those two plugs. That's my thougts. Gotta hit the sack. Good Luck!
If you don't get any power at those two LT GRN/BLK wires, I would think the problem resides in your PNP switch. If you do get power, it is either a mechanical problem with the shifter/tranny or an electrical problem after those two plugs. That's my thougts. Gotta hit the sack. Good Luck!
Thread Starter
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Beginning Member
Joined: Dec 2016
Posts: 16
Also should have mentioned that you want the plug at the PNP connected for the above check. Only the stop lamp switch plug and the plug at the shift lever disconnected.
If you don't get any power at those two LT GRN/BLK wires, I would think the problem resides in your PNP switch. If you do get power, it is either a mechanical problem with the shifter/tranny or an electrical problem after those two plugs. That's my thougts. Gotta hit the sack. Good Luck!
If you don't get any power at those two LT GRN/BLK wires, I would think the problem resides in your PNP switch. If you do get power, it is either a mechanical problem with the shifter/tranny or an electrical problem after those two plugs. That's my thougts. Gotta hit the sack. Good Luck!
Super Member
Joined: Nov 2011
Posts: 1,139
From: Pennsylvania
J., Any success?
Had a thought today, when you checked for voltage on the LT GRN wire at the PNP mentioned in my first response, did you check for voltage with the connector connected and back probe the LT GRN wire or did you disconnect it? If you check the harness side, leave the connector connected and back probe the wire. If you disconnect it check the corresponding pin on the PNP, not the LT GRN wire. If you back probe, disconnect the Stop Lamp Switch and the connector at the shift lever so power doesn't get pulled to ground through those. If you choose to disconnect the PNP connector and check the pin on the PNP itself, you might not need to disconnect the other two connectors. But I'm wondering if innards of the PNP needs a signal from the Stop Lamp Switch to put power out through the LT GRN wire. I don't think so, but tonight if I get a chance I'll try to get another look at the schematics.
Had a thought today, when you checked for voltage on the LT GRN wire at the PNP mentioned in my first response, did you check for voltage with the connector connected and back probe the LT GRN wire or did you disconnect it? If you check the harness side, leave the connector connected and back probe the wire. If you disconnect it check the corresponding pin on the PNP, not the LT GRN wire. If you back probe, disconnect the Stop Lamp Switch and the connector at the shift lever so power doesn't get pulled to ground through those. If you choose to disconnect the PNP connector and check the pin on the PNP itself, you might not need to disconnect the other two connectors. But I'm wondering if innards of the PNP needs a signal from the Stop Lamp Switch to put power out through the LT GRN wire. I don't think so, but tonight if I get a chance I'll try to get another look at the schematics.
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Beginning Member
Joined: Dec 2016
Posts: 16
J., Any success?
Had a thought today, when you checked for voltage on the LT GRN wire at the PNP mentioned in my first response, did you check for voltage with the connector connected and back probe the LT GRN wire or did you disconnect it? If you check the harness side, leave the connector connected and back probe the wire. If you disconnect it check the corresponding pin on the PNP, not the LT GRN wire. If you back probe, disconnect the Stop Lamp Switch and the connector at the shift lever so power doesn't get pulled to ground through those. If you choose to disconnect the PNP connector and check the pin on the PNP itself, you might not need to disconnect the other two connectors. But I'm wondering if innards of the PNP needs a signal from the Stop Lamp Switch to put power out through the LT GRN wire. I don't think so, but tonight if I get a chance I'll try to get another look at the schematics.
Had a thought today, when you checked for voltage on the LT GRN wire at the PNP mentioned in my first response, did you check for voltage with the connector connected and back probe the LT GRN wire or did you disconnect it? If you check the harness side, leave the connector connected and back probe the wire. If you disconnect it check the corresponding pin on the PNP, not the LT GRN wire. If you back probe, disconnect the Stop Lamp Switch and the connector at the shift lever so power doesn't get pulled to ground through those. If you choose to disconnect the PNP connector and check the pin on the PNP itself, you might not need to disconnect the other two connectors. But I'm wondering if innards of the PNP needs a signal from the Stop Lamp Switch to put power out through the LT GRN wire. I don't think so, but tonight if I get a chance I'll try to get another look at the schematics.
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Beginning Member
Joined: Dec 2016
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Hey, sorry I just seen your response here... No dice! BUT, I did just realise why I didn't see any voltage when back-probing that connector on the LIGHT GREEN wire... They have little rubber grommets inside of them that won't let the red probe of the multimeter reach in far enough to get any kind of reading! Stupid me! Because I tried back-probing wires I knew were hot and wasn't getting any voltage either... So I pulled the plug and checked em, seen the little grommets!
Super Member
Joined: Nov 2011
Posts: 1,139
From: Pennsylvania
I believe you should see voltage. Did you install that PNP switch on to the trans. I saw in the manual that if you re-install the original there is a certain procedure and there is a special alignment tool. However it does state that if installed incorrectly the truck won't start. But 's since your truck does start I wonder if it could be out of alignment just enough to prevent the juice to your solenoids. Later tonight I'll look at it some more. Unfortunately I have my Trailblazer in pieces or I would just run some tests so I could be definitive on what you should see.
Also, all of the plugs have those grommets. They're called weather-packs. I have a kit that has needle like probes so you can back probe. However you could use T-pins at better yet they have "Corsage Pins" at Walmart that serve basically the same as the kit I have. You would just want to be careful that the pins stay isolated and do not touch any metal and short the system out. If you want you can go to alldatadiy.com and purchase an annual subscription for your truck for the service manual the dealers use. There you would find all the diagrams and can zoom in. It's less than $20 for the annual subscription.
Also, all of the plugs have those grommets. They're called weather-packs. I have a kit that has needle like probes so you can back probe. However you could use T-pins at better yet they have "Corsage Pins" at Walmart that serve basically the same as the kit I have. You would just want to be careful that the pins stay isolated and do not touch any metal and short the system out. If you want you can go to alldatadiy.com and purchase an annual subscription for your truck for the service manual the dealers use. There you would find all the diagrams and can zoom in. It's less than $20 for the annual subscription.
Last edited by rockp2; Jan 1, 2017 at 03:03 PM.
Thread Starter
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Beginning Member
Joined: Dec 2016
Posts: 16
I believe you should see voltage. Did you install that PNP switch on to the trans. I saw in the manual that if you re-install the original there is a certain procedure and there is a special alignment tool. However it does state that if installed incorrectly the truck won't start. But 's since your truck does start I wonder if it could be out of alignment just enough to prevent the juice to your solenoids. Later tonight I'll look at it some more. Unfortunately I have my Trailblazer in pieces or I would just run some tests so I could be definitive on what you should see.
Also, all of the plugs have those grommets. They're called weather-packs. I have a kit that has needle like probes so you can back probe. However you could use T-pins at better yet they have "Corsage Pins" at Walmart that serve basically the same as the kit I have. You would just want to be careful that the pins stay isolated and do not touch any metal and short the system out. If you want you can go to alldatadiy.com and purchase an annual subscription for your truck for the service manual the dealers use. There you would find all the diagrams and can zoom in. It's less than $20 for the annual subscription.
Also, all of the plugs have those grommets. They're called weather-packs. I have a kit that has needle like probes so you can back probe. However you could use T-pins at better yet they have "Corsage Pins" at Walmart that serve basically the same as the kit I have. You would just want to be careful that the pins stay isolated and do not touch any metal and short the system out. If you want you can go to alldatadiy.com and purchase an annual subscription for your truck for the service manual the dealers use. There you would find all the diagrams and can zoom in. It's less than $20 for the annual subscription.
