Oil light stay on

[swiftwing]

My oil pressure light recently started going on and off at random times and speeds. Sometimes it was on at high rpm when oil pressure should be high and sometimes it was off at idle when oil pressure was low. Yesterday is stayed on almost continuously. With the sender wire off, the light goes out so I know it is not a short in the wire. I suspect the oil pressure switch. I took the switch off and tested it on the bench with air pressure. The switch is closed with no pressure but as I add pressure I get an ohm shift but the switch does not open. Can anyone tell me if I should get a full open circuit on this switch with 30 psi pressure? Any other suggestions before looking for a switch? Other than ebay, where should I look to buy a replacement?

[bikerphil]

If you are sure the oil pressure sending switch is bad then I would replace it. Another thing to look at on the 79 Specials is that the oil warning light doubles as a tail light bulb failure indicator. It all runs thru a light checker unit under the left side plastic cover. Try jiggling the connector plug to this unit and see if the light flashes on and off. The pins in those connectors get loose and cause the oil light to flash on making one think there is no oil pressure. Common problem only on the 79SF.

[swiftwing]

I have checked the tail light and brake light for their operation. I have not fiddled with any of the connections assuming that if the lights work there is no problem with that circuitry. Also, if I disconnect the wire to the oil pressure switch, the indicator light goes out. If the tail/brake light system were the cause, I would think the indicator light would remain lit.

Does this make sense or is my logic firing on only 3 cylinders?

[MPittma100]

Oil Switch

My oil pressure light recently started going on and off at random times and speeds. Sometimes it was on at high rpm when oil pressure should be high and sometimes it was off at idle when oil pressure was low. Yesterday is stayed on almost continuously. With the sender wire off, the light goes out so I know it is not a short in the wire. I suspect the oil pressure switch. I took the switch off and tested it on the bench with air pressure. The switch is closed with no pressure but as I add pressure I get an ohm shift but the switch does not open. Can anyone tell me if I should get a full open circuit on this switch with 30 psi pressure? Any other suggestions before looking for a switch? Other than ebay, where should I look to buy a replacement?

The oil pressure switch is NC (normally closed). With no oil pressure, light should illuminate. I do not know if there is a set pressure on the switch or if it is simply opened by any amount of pressure.

I would think that 30 PSI should open the switch and turn the light off. I would check the oil pressure with a gauge and/or replace the switch prior to riding the bike again.

Pressure switches:

http://www.ebay.com/sch/i.html?_odkw...witch&_sacat=0

[bikerphil]

I have checked the tail light and brake light for their operation. I have not fiddled with any of the connections assuming that if the lights work there is no problem with that circuitry. Also, if I disconnect the wire to the oil pressure switch, the indicator light goes out. If the tail/brake light system were the cause, I would think the indicator light would remain lit.

Does this make sense or is my logic firing on only 3 cylinders?

Yes your logic makes perfect sense, I'm just saying the LCU will sometimes fool the light to go on when it shouldn't, even if all systems are operating properly. GL

[swiftwing]

The oil pressure light and switch are now working again. Here is what I did. Last night I sprayed the working end of the switch with carburetor cleaner. That might have loosened up some deposits in the diaphragm of the switch. When I bench tested it tonight with 30# of air I got an open indication on my ohm meter. At 0# I had a fully closed switch. So I gave it one more shot of cleaner, dried it out with the air hose and reassembled it back in the bike. Everything is working now, but I haven't road tested it yet. So we will see. If it is a temporary fix and the switch needs replacing or that an occasional cleaning will give me and others trouble free service.

Thanks to those who contributed!