Transmission indicator flashes when shifting from forward to reverse

[DREDnot]

I have a 1998 M1078
It had a no crank condition that I traced down to the pushbutton control pad.
Got a used unit off ebay that now powered up and allowed the truck to start.
If you shift to reverse, the trans engages and you back up. Shift to N fine Then when you shift to drive, the 7 flashes and the trans wont engage. Turn off master power and then turn it back on(reboot?) and restart engine and it now shifts to drive fine. shifts to N fine, but then when you shift to R, it flashes till you turn the power off and back on.

Figured we got a bad controller. Seller sent another one. Shifted fine between D,N,R,N,D,N,R N,D,N,R...OK problem solved...till I actually moved the truck backward and tried to shift back into drive and same exact problem.

Anybody seen this before?

road tested OK and shifted through the forward gears like it should.
You just have to shut it down to shift to reverse from drive, or from drive to reverse. It always engages the first direction you select at startup whether its D or R but wont switch between the two. controller just flashes the 7 or R.
I do know to shift to N first between directions per the TM
Both controllers were the same part numbers as the original.
When shifting, I can hear a click coming from the Trans ECM area whether it engages properly or not.

 

[NDT]

Pull the codes. Do you have the Allison book that tells you what the codes mean?

 

[Suprman]

I would start by adding a big ground wire from the battery negative to the large frame rail. Make sure you sand the spot and repaint after.

 

[DREDnot]

Thanks for the replies guys.
I just got back from the storage lot and pulled codes
D1 21-12
D2 21-23
D3 23-12
D4-
D5-

disconnected the battery and inspected the cab harness cannon plug. Condition was excellent but not fully clicked into the lock detent aligning the two red dots. Next checked the connector on the lower front of the transfer case. Same. excellent condition but not fully clicked into the locked detent. Then checked the Throttle position sensor. The connector was barely inserted and one of the pins was damaged and misaligned. I did some surgery on it and got it to connect and seat fully. Reconnected the battery and fired it up.

It now functioned perfectly. Shifted smoother and easier. No more balking between D and R.
So far it seems fixed.

I had already gone through all the ground and power connection points and cleaned them before I did anything to the truck. Even though its a really clean unit out of NM, I always start with main ground and power connection out of habit from years of jeeps and rust.

Thanks again guys!

 

[coachgeo]

congrats on your success..

 

[M1078MAN]

Congrats, good looking rig