The vehicle speed sensor is going bad . That's what is causing erratic shifting an the O/D light flashing .
The back-up lamp system consists of:
- the transmission range (TR) sensor.
- the back-up lamp bulb(s) located in both rear lamp (13404) assemblies
- circuit wiring and circuit protection
Circuit protection is provided to the transmission range (TR) sensor through fuse 30 (25A). This fuse is hot in RUN. With the transmission in REVERSE, the switch closes and power is provided to the back-up lamp bulbs through Circuit 140 (BK/PK). Ground is provided to the back up lamp bulbs through Circuit 57 (BK). The range sensor is located on the transmission at the manual lever.
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how to read a wiring diagram .
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Find free wiring diagrams here ! Enter vehicle info year , make , model an engine size . Under system click on lighting , then subsystem click on reverse lamps . Hit the search button , then click on the link .There is your back up lamp circuit check the fuse , check power at the range sensor switch in an out .