Oil Idiot Light

[idahobilly]

I am having problems with my oil idiot light on my 1974K-4. The light doesn't work at all? My manual claims the light should light with ignition on and go out in three to five seconds (assuming correct oil level and NO internal problems). If switch is defective oil  light will stay on constantly. Well if i ground my switch it will light (rules out bad bulb).If the switch is bad the light is supposed to be on? So do i buy and replace the old switch and hope for the best?...If so where is a good source to get a replacement?

[vern401]

What do you mean by grounding the switch? The sencer or the wire for it? Have you removed the sencer and checked it for sludge plugging up the port?

[idahobilly]

i grounded the sender wire to the engine and the light worked. i have not removed the switch to check for crud but that sounds like a good idea. The switch basically should stay closed with no oil pressure (light lit) and open when pressure moves the spring in the switch(light off)? So maybe the switch is stuck open? Are NOS switches still available? I cannot find a right handlebar switch although power sports list one on the microfiche and EBAY is full of lousy electric parts!  

[vern401]

It does sound like it is probably faulty. I'd take it off and see if I can clean it up some. There is a section on here for parts places to get parts for these old bikes like www.oldbikebarn.com . Some of those sites have the part numbers and tells you if it's even available from honda. If you find it is bad maby post it on the forum that you need one. Somebody on here must have the part you need.

[fpcb750er]

I agree with Vern's suggestion, try to clean it first before replacing it.

One note, be careful, very careful of Oldbikebarn, google them first, look at the posts here and at the other sohc site and come to your own conclusion about their trustworthiness.

[vern401]

You may want to think about using an oil pressure gauge to see what the oil pressure is actualy running. Is a just in case thing. I check mine when I buy them as soon as I can. Oil is to important to the engine to play gessinf games with.

[halfwing]

I have been able to find many many parts on this site. www.bikebandit.com.

Take a look at this page. http://www.bikebandit.com/houseofmotorcycles/1974-honda-motorcycle-cb750k4/o/m9235

[EHondaWins]

Maybe a quicker way to find out is to check the resistance on the wiring.

Tools:
Ohmmeter
Wiring Diagram in the Owner's Manual (or here) (or with the suspect wiring highlighted).

Procedure:
- Put the bike in neutral and make sure the Neutral lamp is working.
- Stall the bike on purpose. This would normally force the Oil Pressure lamp on. Ensure that it does not.
- Turn the ignition off.
- Disconnect the block connector going to the alternator. In the block connector, note the locations of Blue/Red wire, and the Light Green/Red wire.

Check 1) Through the block connector, test the Light Green/Red to Blue/Red wire resistance.

If it's an open lead (or high resistance), go to check 2.
If not, then there is short between the ignition and the Oil Pressure Lamp. That's a whole different post than this.

Check 2) Open the Indicator Cluster (idiot light) box and remove the Oil Pressure Lamp (OPL). Test the Blue/Red wire with the center electrode of the OPL socket (where the tip of the light goes), then test the Blue/Red wire with the side of the OPL socket.  (It's not clear which lead goes to the Blue/Red wire in the diagram so do both. One should be an open lead, the other should not.)

If both leads are open, then you Blue/Red wire probably has a break in it. Test the wire resistance to the barrel connector (shown in diagram) to figure out whether the wire into the Indicator Cluster is broken, or if it's the wire leading to the block connector through the main Wire Harness.
If one lead is open and the other measures a high resistance, then the Blue/Red wire may be corroded or partially broken.
If one lead is open and the other measures a low resistance, go to check 3.

Check 3) Install the OPL back into its socket. Remove the Neutral Indicator Lamp (NIL). Repeat the tests from check 2 except for the NIL socket: test the resistance of the Blue/Red wire with the center electrode of the NIL, then test the Blue/Red wire with the side of the NIL socket.

If both leads are open, then there may be a break in the Black wire running in between the NIL and the OPL, and it may need to be replaced.
If one lead is open and the other measures a high resistance, then the Black wire could be corroded or partially broken.
If one lead is open and the other measures a low resistance, then clean the inside of the NIL socket and the OPL socket using contact cleaner. Plug everything back in, and test the OPL by intentionally stalling the engine.


If the issues persists, you probably have an intermittent connection in your wiring, or I completely misread the diagram.

EDIT: added colored wire diagram and note about barrel connectors.

[hexguy1]

could be the sensor, if grounding the wire to it lights the light. saw one on ebay while back
good luck

[idahobilly]

Thanks to EVERYONE! Well my manual was wrong about light being on constantly on if circuit or sender was bad.As i mentioned earlier the light was good but did not work with key on in neutral. I removed the sender (it looked fine),changed the oil/filter, Reinstalled the sender and still nothing? My local honda stealership did not have a sensor in stock (gee imagine that) but the parts guy told me a 1995 honda prelude switch would work. So I took the bike for about a 60 mile cruise and guess what? It is now working again!! I really dont trust it and i did order a new switch,but a faulty oil pressure switch can be either on always or off always.  

[vern401]

That is a good thing to remember...