Grounding problem maybe

[stapleton]

Was not sure where to post this since I am working on multiple DTC codes but here goes.
My truck has been showing some codes lately like 35,68,74. Before I cleaned the input cable to the tranny I also saw some codes 85,86,87 with an intermittent default to 2nd gear . The default would clear after cycling ignition power.
I have been following the turbo tips for the DTC 35 code and I have been cleaning the grounds. On the firewall stud there are 2 braided straps . One goes to the rear engine bolt but I cannot trace the second smaller braid. Does anyone know where this one goes? Also I found some postings that refer to a ground inside the cab. I have not found it either. I used a haynes manual wiring diagram to check the grounds from the PCM connectors to the battery and all had very low resistance.
Any pointers would be appreciated.

[Robyn]

One of the biggest problems with these trucks when they get time on them is the battery cables.
The side terminal cables corode in the cable strands under the red end jackets and at the crimps.
This applies to both the + and - cables. Even the ground eye where it bolts to the block can be bad and not show.

Make sure you have good voltage at both batteries and at the junction box feed.
Depending on the year of the truck the cable routing and feed loactions are slightly different.
You need a good solid 14V at the main harness or junction box feed.

Many times the grounds at the batteries get flakey on one battery and then cause all sorts of grief.

The body grounds are generally not an issue. The two grounds at the RH rear of the manifold are important.

Be sure your alternator is working right too as a bad diode can drive the ecm crazy.

Check it out and if the cables are old, replace them.

Robyn

[stapleton]

Thanks for the tips Robyn. I will look more closely at the battery cables. I did check the voltages and they seem fine. Showing 13.9 volts. You mentioned the diode on the alternator . I am wondering how I would determine if it is causing problems? Wonder if I could measure AC voltage to see if there is noise on the DC voltage.