Electrical problem..... oil light on! SOLVED!

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Electrical problem..... oil light on! SOLVED!

Postby bugdewde » Thu Jan 16, 2014 9:06 am

Oil light came on yesterday.... oh crap! Full on, not a flicker.
Had plenty of oil.
Noticed tach was not working.
Seemed gauges(original GT fuel, temp, ammeter) were stuck and not working either.
Blinkers weren't working.
No strange noises from engine.......... so I assumed an electrical problem developed. After a couple attempts at starting and trying to determine if i actually did have pressure, I attempted a 25 mile run home. Success!!!! No strange noises or engine lockup occured. Whew!
It was quite cold last night, so I didn't check anything electrical when I got home.
What would be my best starting location at diagnosing this?
Bad relay or blown fuse? I'm stumped. Figured light wouldn't work at all if fuse or relay was bad......?
Last edited by bugdewde on Fri Mar 07, 2014 8:29 pm, edited 1 time in total.
Dwight

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Re: Electrical problem..... oil light on!!!!

Postby Monza Harry » Thu Jan 16, 2014 9:35 am

Dwight I would start by unplugging the oil pressure switch and using a jumper wire first determine if it is the switch (and check fuel pump function while your at it) assuming this has an electric pump(?) but it runs with the light on so maybe no on elec. pump? If this is a single wire switch unplugged should be no light , grounded should result in a light, that will verify vehicle wiring. Then test switch no pressure it should show continuity to ground, with pressure it should be open (no continuity). You could remove the switch and put in a test gauge just to make yourself confident your pressure is good (just for good measure) Your other issues will need further investigation. The cold does some strange things to a car, a lot harder to guess at than heat problems. If I had to guess I would look for a loose plug ("Shrinkage" George Castanza) maybe only half is still touching in the dash Printed Circuit, the non functioning gauges is usually a no power situation but could be a loose ground as well. As an after thought I have seen a sludge build up at the switch port on an unmaintained car or two you know not allowing the oil to get to the switch, these cars had all sat for awhile as well but you are driving yours in January so I take it yours doesn't sit much(?) just a few ideas to think about/try. Harry
[EDIT] Sorry disregard the fuel pump stuff as I remember you don't have a Monza (or cousins) Vega's were all mech. pumps
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Re: Electrical problem..... oil light on!!!!

Postby bugdewde » Thu Jan 16, 2014 12:32 pm

Thanks.... I'll check for continuity and determine the switch effectiveness.

All 140 powered Vegas have intank electrical fuel pumps that get power from the oil pressure switch. I think 151 iron duke powered cars might have mechanical pumps.....

My intank electrical pump works intermittantly. How I bought it (about 7 or 8 years ago). I installed my "emergency" external electric fuel pump on the firewall ..... getting power from a solenoid on the carb when needed. I have had it hooked up for lately for about 500 or so miles...... negating intank pump issues.

A few years ago, the oil sender went bad, leaking oil out of the bakelite/plastic around the elect terminals. I replaced it with an aftermarket sender from ebay(I think).... as I couldn't find an oem one. Could be bad.
Just stumped by all the other gauge/blinker/tach issues that just popped up with the oil light issue.
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Re: Electrical problem..... oil light on!!!!

Postby cosvega76 » Thu Jan 16, 2014 5:44 pm

Dwight,

Here is the explanation of the fuel pump/oil light circuit I posted in an earlier thread:

The oil pressure sender circuit is unique in the Vega, because of the electric fuel pump. One terminal is connected to the start circuit between the ignition switch and the starter, one is from the oil light on the dash, which is also connected to the fuel pump, and one is connected to the Fuel Pump Run fuse (12v switched). With no oil pressure, the fuel pump/oil light circuit is connected to the starter circuit through the OP switch internally. Energizing the starter sends power to the fuel pump via the fuel pump/oil light circuit through the Fuel Pump Start fuse. Once oil pressure is established, the oil pressure switch connects the fuel pump/oil light circuit to the Fuel Pump Run fuse circuit.

Since there is power on both sides of the oil light, it does not illuminate. If the oil pressure drops below the threshold, the connection breaks between the Fuel Pump Run and fuel pump/oil light circuits and the oil light is grounded through the fuel pump and/or starter solenoid. Since there is little current supplied because of the resistance in the light bulb, there isn't enough to supply either the starter or fuel pump and does not energize either one.

Believe me, it took me a long time to figure this one out! Pretty ingenious circuit design!


If it would be easier to understand, I can post the circuit drawing I made up.

My Vega had this intermittent oil light on/ no fuel stalling problem that made me pull my hair out. All it took to fix it is squeeze the terminals in the OP switch socket so they would make good contact.

Here's the diagram, it may help it make more sense (right-click on "view image" for easier viewing):

Fuel Pump Schematic.JPG



Chuck
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Last edited by cosvega76 on Sun Jan 19, 2014 9:04 am, edited 1 time in total.
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Re: Electrical problem..... oil light on!!!!

Postby cjbiagi » Thu Jan 16, 2014 7:30 pm

Obviously it is a electrical problem that most likely has nothing to do with the actual oil pressure. Most likely a bad ground since so many things have been affected. Spence can probably offer the best advice, but it's always a good idea to run a nice heavy ground wire from the engine block to the chassis. That's a good start, otherwise you are going to have to start checking ground wires under the dash.
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Re: Electrical problem..... oil light on!!!!

Postby cosvega76 » Sun Jan 19, 2014 9:12 am

Previous post edited to add schematic diagram, see above.


Chuck
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Re: Electrical problem..... oil light on!!!!

Postby SeniorSavage » Sun Jan 19, 2014 8:32 pm

FYI ; one of these should help ya - I also full-screened Chuck's drawing for easier comparison.

if you have a V8 in there if you tell me what model it came from I can also post a diagram for that year and model .

Cheers and good luck.

Todd
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Re: Electrical problem..... oil light on!!!!

Postby marco_1978_spyder » Mon Jan 20, 2014 8:33 am

Before the issue started, what was the last area of the car that received some tinkering? Start there.
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Re: Electrical problem..... oil light on!!!!

Postby bugdewde » Thu Jan 23, 2014 8:23 pm

No work on car yet..... been too cold for me to actually do anything but think. Driving the nice, warm, comfortable GTO.
Marco, you might have jogged my memory. A month or so ago, I changed the thermostat. Old one was the fail-in-the-open-position kind, and it did.... no heat. While changing it out, a previous owner splice of the temperature gauge sender wire came undone. I didn't re-crimp it in the hurry... just stuffed the wire up in the splice thingy.... temporarily. May have vibrated loose.... as this car vibrates like crazy. I'll have to get out there and pop the hood and check when it gets above freezing.... supposedly sometime next week.... this TN boy doesn't do cold weather well.

Guys, thanks for the diagrams and the explanation.... they will be helpful.

Clyde, I have the original ground strap from the cylinder head to the firewall that I re-installed when I had the head rebuilt.
Hate to crawl under the dash but it looks like I'll have to.... might as well disassembe it some so I can get the HVAC fan switch re-installed (I tried from under the dash but I don't have 12-year-old Asian female hands). Might has well replace those tired instrument panel lights, too!

I'll post what I find once it warms up.
Thanks again guys,
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Re: Electrical problem..... oil light on!!!!

Postby marco_1978_spyder » Thu Jan 23, 2014 8:55 pm

That old saying has helped me more than once.

Not only the vibration, the engine fan probably makes a windstorm in the compartment @4000 rpm with the hood closed.
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Re: Electrical problem..... oil light on! - SOLVED

Postby bugdewde » Fri Mar 07, 2014 8:27 pm

Problem solved. :th: Only took 6 or 7 weeks for me to actually look at it.... lol.

Two blown 20A fuses found.
1) CLK LTR CTSY - explains why my clock, lighter and dome light quit working (now working).
2) SIG-B/U GA-TCS - obviously turn signals, back up lights and gauges (now working)..... what's TCS? (transmission control switch?????.... disconnected when I swapped in the 5-speed).


Still not 100% sure why oil light was powered.... may be part of the GA-TCS blown fuse???? Obviously, since it's all good now.

How it's supposed to work: (If I read Chuck's diagram correctly)
---The "start" fuel pump circuit (no oil pressure) and starter gets power from ign switch across the radio fuse (radio was working while this was going on????) and the oil light (was not on with ignition on.... so no "start" fuel pump).
---Once oil pressure is detected (OP switch closed) the ignition switch powers the "run" fuel pump circuit..... cutting off the "start" circuit when the oil pressure light/oil pressure switch is closed.

How mine was working:
Turn ignition switch to "on".... no oil pressure light (supposed to be on).
Turn ignition switch to "run" ... oil pressure light goes on.
Just opposite of what it was supposed to do. Maybe since the gauges fuse was blown, there wasn't any oil light power until the oil switch powered it when it closed.... kinda getting in the back door??????

Thanks again for all the input and diagrams.
Marco, I re-crimped that water temperature sender wire.... maybe it won't blow any fuses if it comes undone again!
Dwight

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'73 Vega Wagon - Currently in Limbo....
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Re: Electrical problem..... oil light on! SOLVED!

Postby cosvega76 » Sat Mar 08, 2014 8:52 am

Dwight,

Did you mess with the socket on the oil pressure switch? Mine turned out to be a bad connection to the terminals on the switch.

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Re: Electrical problem..... oil light on! SOLVED!

Postby bugdewde » Sat Mar 08, 2014 9:13 pm

cosvega76 wrote:Dwight,

Did you mess with the socket on the oil pressure switch? Mine turned out to be a bad connection to the terminals on the switch.

Chuck


Only to wipe some oil and buildup off the wires. I'll pull the gauges fuse and see if it replicates the condition.
Dwight

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'73 Vega Wagon - Currently in Limbo....
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Re: Electrical problem..... oil light on! SOLVED!

Postby cosvega76 » Sun Mar 09, 2014 11:57 am

I had to take pliers and squeeze the female terminals on the inside of the plug so they would grip the male terminals of the switch better. It was hair-pulling time before I found that was the problem.


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