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Premium Member
1981 CX500B
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39 Posts
Discussion Starter · #1 ·
Hi all, I have finished the cam chain, mechanical seal and cleaned out the oil strainer. The engine is back in the bike and sounds great. The only problem I have now is the oil pressure switch. I did not remove it when I removed the front cover, only unplugged it from the wiring harness. I have 12v going to the switch. Could the switch really be at fault?
 

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24,013 Posts
Check the connections. At the sender and at the air dam on top of the motor.
 

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5,881 Posts
You shouldn’t have voltage at the switch.
Shouldn't there be 12 volts on the blue/red wire at the oil pressure switch? No current flow when the switch is in the open position, current flow and warning light on when the switch closes and provides the connection to ground?
 

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The power is fed to the globe and on to the switch to be grounded when oil pressure drops below around 4 - 7 PSI.
 

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Shouldn't there be 12 volts on the blue/red wire at the oil pressure switch? No current flow when the switch is in the open position, current flow and warning light on when the switch closes and provides the connection to ground?
I don't have the service manual in front of me but I thought the 12 volts would be at the bulb and the switch provided the ground to illuminate the bulb.
 

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Premium Member
1981 CX500B
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39 Posts
Discussion Starter · #11 ·
Just did a few miles. Engine runs well, I have no leaks anywhere which has surprised me. I thought there should be voltage in the wire to make the circuit.
 

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There is and you have verified that it is reaching the switch. Take the rubber boot off of the switch and use a short length of wire to ground the switch wire.

If it lights the switch is faulty.

Doug, the power delivered to the switch is low, being limited by the bulb it is going through. At a rough 4.5 watt for a warning light bulb at 12 volts current is only about 1/3 of an amp.
 

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Premium Member
1981 CX500B
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39 Posts
Discussion Starter · #13 ·
Grounded the switch wire and the light came on. Ordered a new switch. Very strange how the switch stopped working when it worked fine before removal of the engine
 

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Maybe check from the switch body to another ground source that the switch is in fact grounded to the rest of the engine.

I get hit with left field [email protected] all the time.
 

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Premium Member
1981 CX500B
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39 Posts
Discussion Starter · #17 ·
Gave it an hour in a heated ultra sonic tank at 80 degrees. It worked first time. Light went out as it started. Stopped working only dimly lit on a second start a few minutes later. At least I know its the switch that's faulty.
 

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Premium Member
1981 CX500B
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39 Posts
Discussion Starter · #20 ·
The switch was rusty and probably the original. I've been out on the bike for a longer run today and broke down. The engine died instantly as I stopped at a junction. The engine spins over but there is no spark. I did a stator test as follows
1/5 95-116 113
2/5 81-99 95
3/5 185-225 nothing
4/5 95-116 113
6/5 81-99 95
7/5 185-225 nothing
8/9 77-95 84
5/9 387-473 311
Green/white 387-470 311
Blue/white 77-99 84
Blue green 395
Got a feeling this engine is coming out again. The bike ran great for 27 miles.
 
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