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3116 AO oil sending unit
- Thread starter chucky
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Ronmar
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On the A0/early A1, There is a gauge sending unit for the gauge and a switch that controls the idiot light and alternator @15PSI.
the A1R uses bussed gauges that mostly display ECU sensor data...
On the older electric gauges, Jumping around could be a loose connection. All of these gauges are current meters, and the senders are a variable resistor that vary with pressure or temp, so the test is to connect a known fixed resistor with a value in the middle of the sensors resistance range to give a mid scale reading on the gauge needle. Put this resistor in circuit in place of the sender(sense wire to resistor, other end of resistor to ground), and see if it still jumps around when driving. If not it is a bad sender or connection re-attach and try the sender again. if it still jumps with the test resistor in place attach it at the back of the gauge and try again. Still jumpy, bad gauge or bad power supply feed or connection to gauge. If it is stable, probably a bad connection somewhere between gauge and sender...
the A1R uses bussed gauges that mostly display ECU sensor data...
On the older electric gauges, Jumping around could be a loose connection. All of these gauges are current meters, and the senders are a variable resistor that vary with pressure or temp, so the test is to connect a known fixed resistor with a value in the middle of the sensors resistance range to give a mid scale reading on the gauge needle. Put this resistor in circuit in place of the sender(sense wire to resistor, other end of resistor to ground), and see if it still jumps around when driving. If not it is a bad sender or connection re-attach and try the sender again. if it still jumps with the test resistor in place attach it at the back of the gauge and try again. Still jumpy, bad gauge or bad power supply feed or connection to gauge. If it is stable, probably a bad connection somewhere between gauge and sender...
Where is the sender that runs just the gauge located on the motor ? Is it the one pointing at you or the one thats sideway by the block ? Before i start pulling these old wiring boots apart that usally crumble i will try to not tamper with any thing i dont have to !
Last edited:
Ronmar
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THe larger one with the single wire connector is the gauge sender.
The smaller 15PSI switch is metal and plastic should have the name "Nason" on a sticker. it has a 2 wire connector(one to ground, one up to the dash)...
The smaller 15PSI switch is metal and plastic should have the name "Nason" on a sticker. it has a 2 wire connector(one to ground, one up to the dash)...
Thanks
Sure enough the wire might have had 2 strands stuck in the crimped round terminal going into the sending unit ! That the second terminal crimp so far on this truck that must have been done by the blind my ignition wire took 3 yrs to find bad crimp to be able to start the truck from the drivers seat . Must have been a friday 4.30 in the afternoon build at stewart stevenson for my truck !
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I think every day was a Friday at the S&S facility. Chrysler got all the news reporters filming their guys with brewskies and J's on lunch and before their shifts and diverted the attention for everyone else.
I've found SO MANY wiring deficiencies with these trucks (mine, friends, and even A1P2's from Oshkosh), The wiring is atrocious. That's why my go-to response for everyone's questions about why their truck doesn't start, charge, and bring the light is to CHECK YOUR CONNECTIONS. First task for every new FMTV civilian owner should be to spend AT LEAST A WEEK addressing electrical connections on the whole truck.