CrashCade

I am having a problem with my truck showing neutral or 1st gear on my dash. This only started after my last rebuild. The tranny seems to do everything it is supposed to, but I cannot get it to show Neutral, which means I cannot get my truck to go into 4LO. If I put my truck in neutral it will not show, but I can still shut it off and start it while in that position just no indicator showing it. Is this something internal in the tranny that needs to be looked at or is this a fairly simple fix. Anybody have any ideas or suggestions.

There are sled pulls here in BlackFoot, ID this weekend and I wanted to try my luck for the first time ever, but I can't get 4LO to engage.