The Stovebolt Site Forums The Shop Area The Electrical Bay Hour meter install

I want to keep track of the run time in my newly rebuilt 235. Can I use a GM oil pressure switch to power the hour meter, only when the engine is running? Does this type of switch make or break the + or - power to the gauge.

Yes, you can use it for that. The switch grounds with oil pressure. Use it to ground a relay to power the meter.

Wrong- - - -a regular oil pressure switch grounds with no pressure, and open-circuits when running to turn the light off. There is a 3-prong switch used on GM fuel injected engines with two normally-open contacts, closed by oil pressure. Wire one contact to a constant 12V source and the other to the input of the hour meter. There is also a normally-closed ground for an idiot light that won't be needed for your application. Try looking up an oil pressure switch for a 1976 Vega- - - -that's the one I usually ask the computer jockey nose-picker for at the big box parts stores.

Like this:

http://www.rarenosparts.com/assets/images/BOXA18146.JPG

Jerry

This fuel pump oil pressure switch completes the circuit when it "feels" the oil pressure (4psi and higher). I used it to supply power to the electric chokes on a dual-carb set-up. It is rated for 12v but it works fine with 6v.

It looks like the part has changed - it shows 3 contacts but I think that mine has 2 contacts.

Here is a 2 contact switch.

Either one will work for an application that's oil pressure activated. The 3-pin switch with the built-in ground is used as a dual-purpose item to also provide a ground for the idiot light.
Jerry

Which Hour meter are you running?

I purchased it from e-bay...round face 2 inch 8 to 80 volts. Two poles one + and one -. I am still some what confused as to which wire to hook to the oil pressure switch...and which oil pressure switch to purchase

Connect the (-) terminal of the hourmeter to ground and connect the (+) terminal to one of the connectors on the pressure switch. The other connection on the switch gets wired to either the (+) side of the coil or a constant hot 12V source. As soon as the oil pressure comes up, the hourmeter will run. Try an AC-Delco # D1834 switch. It's the 3-prong type that I use regularly. Use a multimeter on the ohms setting to find the two prongs that have continuity with pressure on the switch, and ignore the grounded one.
Jerry

Tim the two position switch you refer to from NAPA is 1/4" NPT

http://www.napaonline.com/Catalog/CatalogItemDetail.aspx?R=MPEOP6620SB_0306379251

The 3 prong Jerry suggests is the way to go. If I am correct, with that switch, you can remove ground on pressure, or connect ground on pressure, or connect continuity on pressure. Good price too.

In my application, an adapter had to be used (with the other/first switch I listed). I found a brass T that allowed connection to the oil-pressure-source, the oil pressure gauge, and the pressure switch (for current to the chokes).

OK, I have to ask, how many hours are you going to leave the ignition switch on without the engine running?
I have always connected hour meters to the ignition.

I am ready to purchase the oil pressure switch to control my hour meter. Are all 3 prong switches the same? Should I be looking for a specific one that will control the + voltage to activate when oil pressure is measured. I really would like to get one that fits my 235 block.

The AC Delco switch I listed above has a 1/8" pipe thread and works with the stovebolt oil pressure port and a T fitting. That's about as simple as it gets- - - -pressure gauge, oil filter and switch all on one port, using two T fittings. The best T fitting will have one male thread and two female openings. Any FLAPS with a good brass fitting assortment should have them in stock.

http://www.amazon.com/MettleAir-107-A-1PK-Street-Fitting-Female/dp/B0081S14NU

Jerry

CRL, thanks for the idea! It seems like a good idea having an hour meter on any engine. I can see that being a help to determine oil change intervals too as a second check. Anyway, here is the writeup. This should answer any questions pertaining how to do it.

http://devestechnet.com/Home/WarningSystem#HourMeter

Thanks again! It COULD have been something that threw an enormous wrench in the machinery for the rest of that article but turned out to be the perfect compliment to it.