Topic: Bench Testing a 750 Oil Pressure Switch?

[Lucien Harpress]

What is the correct way to bench test an oil pressure switch?  I think I've got it, but just to confirm:

-At rest, outside the bike, there should be continuity between the top screw and the housing.

-With air pressure into the small hole on the bottom (via air compressor), this continuity should go away.

Sound correct?

(Reason being, I have a pressure switch that works kinda wonky, and I've narrowed it down to the switch for sure.  I turn the bike on, and my oil pressure light is off.  It stays off if I run the bike, but if I allow the bike to warm up, it functions as normal- off while running, on once the engine stops, off again if I start the bike again.  If I let the bike cool down, the light fails to turn on with the engine off until it warms up again.

I've also got a replacement switch, but sitting on the bench I'm getting no continuity between the top and the housing.  So that might be broke too.)

Thanks!

[MauiK3]

That sounds about right since the pressure turns the light off. Be careful with how much pressure, about 10 psi should break the continuity, maybe less. Use a regulator.

[Tracksnblades1]

You’re correct, same as the manual.

Switch breaks continuity on a pressure rise (light goes out). Manual indicates the oil light will go out at 7.1 psig or higher..The oil pump relief spring is set to maintain 56.9psig at 4,000 rpm with 176*f oil temp.

Your sender will see the same psig range that your crankshaft bearings do..

[BenelliSEI]

Your procedure is correct. The one on the bench should show continuity. Your old one may be plugged with sludge, that frees up when warm. Try repeatedly blowing it out with some aerosol brake clean?

[HondaMan]

If you are testing the switch with a digital ohmmeter, it may not be giving you a correct reading. This is VERY common with DVMs. The reason is: the contacts in the switch are silver (or silver-plated) copper, which self-protect from atmosphere effects by creating a slight oxide on themselves. This is normal, but it does prevent the very low current of a DVM from measuring it as 'closed' in many instances. This is also common with all other automotive switches, except those that are gold-plated to directly connect to a computer, so the confusion continues...

The best way to test these is to apply their "minimum-rated current" to the contacts. What this means is: hook up a little light bulb circuit to it and run at least 3 volts through the circuit to check its OFF-ON state.

This is a common situation - and sadly, one I have had to explain MANY times to college grads who came to work for/with me on various machine control systems I have built over the years.