Cat-426 crippled with warning horn

1987 #7BC01181, early series with Perkins engine

Wouldn't you know it, 1st day of winter! This morning about 30 minutes after start and some light snow-work the warning horn sounded and the oil light lit up, first intermittently . When sounding the tractor wouldn't move. Ultimately the condition became steady and tractor became immobilized. If I wait and restart half an hour later I get a few seconds of mobility, using this and some downhill I managed to park myself out of my own way.

This is news to me, the oil light and horn never stopped me before. The pressure is 70psi on a good aftermarket electric pr. gauge. I tried to find the pr. SWITCH but cannot locate it on the engine. Anyway I'm not sure if this is an engine problem at all, may be a transmission issue but there's no info in the operator manual or the parts manual. The transmission oil quantity is good. The shop manual has a very short TS note about "low transmision oil pressure" i.e. oil pump failure or suction leak, period.

Right now the tractor is half a mile from house until I manage to tow it in.

Any hunches or experience?

I just towed it in with my Tundra, a bit of a task being all by myself but it's done. The tranny oil BTW is very clean. As far as the engine oil pressure SWITCH would/could bde concerned, it's possible that the oil-pressure TRANSMITTER took its place in a left side engine block port just above the oil filter.

I have a 1989 426 that I am currently doing some preventive maintenance on. I have not gotten to engine stuff yet. I am still repacking all the cylinders and straightening out hoses and pipes. The boom hoses were all rigged up and some of the hard pipes were missing and replaced with hose. I am trying to get it back to stock.

I do have the repair manual. If you don't I highly recommend you buy one. If you need some info in the mean time I can copy a page or two.

fitterski said:

1987 #7BC01181, early series with Perkins engine
ny hunches or experience?

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i made the mistake of posting on 2 forums, it's also up where i've been a member longer

https://www.tractorbynet.com/forums/construction-equipment/419397-cat-426-oil-light-horn.html

I was reading your post over there.

You installed an aftermarket mechanical oil pressure gauge. I am guessing the you removed the low oil pressure switch to install this gauge and the wire is dangling and over time has worn so it is grounding out out simulating a low oil pressure condition.

Pro mechanic installed it, I asked him what he remembers, answer "nothing". It takes a while for the horn & lite to trigger, during this time fwd/bck reaction is already degrading. Once the horn and lite trigger they stay on and machine is stopped, not consistent with rubbing which would be irregular. I'm just trying to eat my way through the wiring diagram to see what I might be able to locate. It has these connectors with letters like ED or GH, I guess these mean some kind of position but I have no idea how to read them.

fitterski said:

I just towed it in with my Tundra, a bit of a task being all by myself but it's done. The tranny oil BTW is very clean. As far as the engine oil pressure SWITCH would/could bde concerned, it's possible that the oil-pressure TRANSMITTER took its place in a left side engine block port just above the oil filter.

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Resolved:
The last pro who has been working on the machine for 10 years also installed the pressure gauge and had then decided to MOVE the presure-switch to the tranny filter. The horn went off a little late each time to be an 'alert' when a dirty strainer caused a self-induced vacuum leak. The strainer was last replaced in 2006 by the former pro who now has the ball again. I'm not equipped to do anything on trannies so I didn't even try.

Thanks for the offer to help out and the comments!