I have a 4l80E behind a 5.3. 5.3 Computer, Painless harness 60217, tuned to my setup. I have been having an issue with the trans shifting into 3rd (and 4th) and holding the gear. I have installed a "manual electric harness and I am able to shift through all the gears without issue when I manually apply the ground to the solenoids when needed. After connecting the original plug back in, I checked the voltage using the ignition as my 12v and the solenoid outputs from the computer (Red connector pins 47 and 48) as my grounds. I get a reading of 12v when testing solenoid A (and the computer is calling for it), But I only get 5v when testing Solenoid B (and the computer is calling for it). I have checked my grounds a few times and even went through the trouble of adding more grounds to block and body/frame. I tested all grounds going into the computer and they tested fine, 12v. I even got another computer and flashed it with my tune and have the same issue. Have any of y'all experienced this issue before?

My work around Idea is to get a 6v relay and have the 5v ground coming from the computer be the activator (hopefully the 5v is enough to activate the 6v relay) and have it deliver a solid ground that will give me the full 12v.
Any help at all would be greatly appreciated. Thank y'all for your time and experience.

 

In a stock/ OEM configuration... the positive connection to the solenoids would constant from a switched ignition source.
The negative connection would be controlled by the PCM.
In this situation; inspecting the wiring, connectors, and pcm for:
-broken connections
-loose connections
-Corroded connections
-Shorted connections

More than likely there is high resistance somewhere, in the circuit that supplies the negative connection to that solenoid; thus the lower voltage.
The transmission case connector terminal "B" is for the circuit being discussed.
Inspecting that wire into the transmission to the solenoid is quick and easy to inspect.
You must also inspect from there all the way to the PCM, as well. (or in your case... to the manual-shift harness, or whatever it is)

Note: due to the mass-production of these Painless brand wiring harnesses...
It is common to find a loose/ incompletely crimped terminal or terminals in the various connectors.

I would double check all of the connectors regardless, since this is a common occurrence with harnesses by Painless.

Without getting into your 6v relay idea... Sorry, I don't want to go there...

How about some information please.

Vehicle year, make, and model.

Battery positive cable/s attach to what/ where?
Battery negative cable/s attach to what/ where?

Does the alternator have a dedicated ground cable to the battery (just like the positive cable does)?

What do you have for negative cables/ straps connecting to the engine?
Do you have a ground strap connecting to or near the transmission?

The "Big 3 Upgrade" as most call it... is very important on older vehicles and/ or vehicles that were originally built with a low out-put alternator.
Also the "Big 3" should really be the "Big 4".

Separate cables:

-New Batt. Pos. to starter motor.
-New Batt. Neg. to engine cylinder block.
-New Batt. Pos. to alternator.
-New Batt. Neg. to alternator.

Also required:

-Batt. Neg. to frame or body (uni-body vehicles).
-Engine Neg. to frame or body (uni-body vehicles).
-Engine Neg. to Transmission/ Transfer Case.
-Batt. Positive to power distribution center/ bussed electrical center/ fuse panel/ ignition-switch/ exterior lights-switch... ETC.

 

You are amazing. Thank you for the long and well thought out reply.
I will again check for: broken connections, loose connections corroded connections, shorted connections more thoroughly and see if I can identify any issues.

Vehicle year, make, and model.
1959 Chevy truck
Battery positive cable/s attach to what/ where? all connected at starter bolt
Battery negative cable/s attach to what/ where? Heads, and frame/body

Does the alternator have a dedicated ground cable to the battery (just like the positive cable does)?
No, I have a connector that clicks into the alternator, and the 12v cable.

What do you have for negative cables/ straps connecting to the engine?
1/0 Cable
Do you have a ground strap connecting to or near the transmission?
Closest is head

I am getting 12v when I test the wire that grounds for solenoid A, but the wire for solenoid B is only 5v. I believe my issue could be in the painless harness. I will FULLY inspect the harness and wires. I did a quick inspection, but I didn't think about pulling back the connectors and checking their work. Thank you a ton. I will get back in town in a couple weeks and will update you on what I find.
Again, thank you a massive amount in the help. I have had the truck in the trans shop for 2 months trying to figure out the issue.

 

You are most welcome!

Good luck!

 

Well, today I ran 4 more big grounds to the frame and block and rechecked all the ground crimps. I even ran jumpers to the 4 different ground wires on the PCM to see if it would help. No such luck. I do have most of my grounds that go to the computer and misc stuff connected to the heads at different spots. but saw no change when installing another large ground from battery.
I checked both solenoids and got a 25.7 and a 25.9 reading (supposed to be between 20-40 so I think they are both good *also they are new*) checked them again at the computer, and got readings that were close to each other.
I use a meter to test the DC voltage from a 12v source (at ignition and battery) to the wires (grounds) that are coming from the PCM to the trans and telling the solenoids to activate. The wire going to the "A solenoid" (using it as a ground wire and only taking a reading when the PCM is calling for it) is giving me a reading of 12v, but I am only getting a reading of 5-6v when tested the exact same way on the wire going to the B solenoid. I have tried 2 PCMs, and get the same result on both. Is there anything that can be tune related? I am not using a PRND as my neutral safety switch if that matters, i am using the lokar shifter that has a NSS located on it.
I am at wits end and honestly ready to just install a 6v relay. Using the ground that is going to the trans as my activator, and make it apply a good ground to the B solenoid.
I drove the truck home from the trans shop using a "manual harness" that gave the trans 12v like normal through the connector, but I had to apply the grounds manually to shift through the gears to get home. So I know the B solenoid will work when given a good ground so I can shift into 3rd and 4th.
Anyone have any thoughts? Is there something I am missing. I am willing to check the computer connectors or harness wire by wire, but I don't know what the readings should be for certain things, or if they even work in conjunction with the trans and/or the solenoids. Any help would be appreciated.

 

The 12v positive side, is a shared circuit for both shift solenoids.

The 12v negative side, are individual circuits for each shift solenoid.
The ground is completed by the PCM.

Since the shift solenoid resistance is good.
I would measure the resistance of the 12v negative wire that goes to the solenoid.
Measure from the solenoid connector to the PCM terminal.

You should only have about 0.002 to 0.004 Ohms if GOOD.
I would think the resistance across that wire would be much higher; and be your issue.