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Oil pressure guage blowing fuses
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rpacker
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Dec 13, 2008, 11:05 AM
Post #1 of 13
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Oil pressure guage blowing fuses
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I have a 66 Fairlane - 302 and for some reason whenever I try to hook up an oil pressure gauge (new, not stock) it blows the fuse. I've tried to simplify it just to get it to work at all by connecting the 12v wire to the battery with an inline fuse. And then connecting the other wire to the oil sending unit. Every time it blows the fuse though.
This is the gauge, it says about a negative post for a ground wire but there isn't a negative post (just the place you can use the mechanical (tube) connection).
I tested the wire and it's at about 12v. I did try to ground it using that middle (mechanical tube fitting) post. I also tried to disconnect the other wires from the solenoid so nothing else would be live in case one of those had a short. Also, I have an idiot light that is connected to a T fitting on the block with the gauge sending unit. This seems to work fine (or at least ligths up when you turn the key and goes out when the engine starts w/no blown fuse). I tried to remove both of the wires from the oil light and oil gauge sensor and just connect my test wire to the oil gauge sensor. But still blows the fuse. Any idea why/how it could be blowing the fuse?
Thanks,
Rob
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Dec 13, 2008, 11:36 AM
Post #2 of 13
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Re: Oil pressure guage blowing fuses
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Hmmm? Not quite sure what you have in front of you but 302 didn't begin till MY 1968 and all the Fairlanes I ever knew of just had an oil warning light. The sender for just a light was just a dead ground I think when pressure dropped below about 20psi or so and would be a short. For a gauge you need a sender the matches the gauge. The "idiot" light and guage idea it totally different at the dash or receiving end........
T
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rpacker
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Dec 13, 2008, 11:51 AM
Post #3 of 13
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Re: Oil pressure guage blowing fuses
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Right, it was a 289 but it just had the oil light also. I think the 302
is around a 76. Where the oil light sending unit was in the engine, I
added a T fitting and put in the old sending unit (for the light) *and*
a new sending unit for the gauge.
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Tom Greenleaf
Ultimate Carjunky
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Dec 13, 2008, 12:40 PM
Post #4 of 13
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Re: Oil pressure guage blowing fuses
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?? The engine itself isn't the issue and the "T" is fine - you could have both. Whatever sender used needs to be wired to match up with whatever gauge you are using. I don't know what to say except I think it's possible the sender for gauge is a dead short - try unplugging it and see if fuse doesn't blow.
It's hard to know just what you are doing with what. Oil gauge sending units are generally like dimmer switches giving gradients of ohms that are ground. Some oldies were all mechanical and literally run a tube with oil in it to dash!
T
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rpacker
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Dec 13, 2008, 1:13 PM
Post #5 of 13
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Re: Oil pressure guage blowing fuses
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I guess my understanding stops at "dead short". Just for testing right now, I just have (2 wires) a wire going from the gauge sender to the gauge and a 12v to the gauge. (note: I have disconnected the light sender and the wire that was using the 12v when key on). My oil gauge does actually have the inlet for the oil tube but I didn't want to do that (since I'd be the one with the 180 degree oil leak later...). I guess the gauge isn't really necessary, I just thought it would be nice to have a more accurate reading than the light.
I just got some more fuses so I'll test some more...
Thanks,
Rob
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rpacker
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Dec 13, 2008, 1:40 PM
Post #6 of 13
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Re: Oil pressure guage blowing fuses
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hrm, well I tried again without the light sender wire attached and it didn't blow a fuse (must not have done that before). Started the car and the fuse is good, but still no oil pressure reading *sigh* The oil sender is new though... dang it.
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Tom Greenleaf
Ultimate Carjunky
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Dec 13, 2008, 1:45 PM
Post #7 of 13
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Re: Oil pressure guage blowing fuses
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An attempt at an analogy of resistance for a gauge: Think of the sender as a ground with varying amounts of ground available depending on the pressure it senses. Power is needed to that ground and if partial (like a dimmer does to a light) then a needle gauge points just as far as the amount of grounding it gets will allow. It's measured in OHMS.
Either way it still shouldn't be blowing fuses. When a gauge wire is hooked up to the idiot light style sender it would just read fully nothing or "pegged" as the sender is basically just ON or OFF - not various amounts of on and off like a sender for a gauge.
You shouldn't be blowing fuses so something is wired incorrectly. You can make up a jumper wire with a breaker for a fuse for testing so you don't have to waste a ton of fuses to keep checking.
IF - check this - If it doesn't blow the fuse when unplugged then try making the connection thru a test light which is "resistance" just to see if the gauge now reads something partial for you - not just either extreme.
This is tough for me as I just don't know the what and how of what you are wiring in for this.
Hey - it's not all that bad just having the quote "idiot" light. I'm an airhead myself and will take notice of a light much sooner than seeing a guage going wrong if it didn't shout at me! Agree with you - I like to have BOTH,
T
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Loren Champlain Sr
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Dec 13, 2008, 2:07 PM
Post #8 of 13
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Re: Oil pressure guage blowing fuses
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I've read the posts on this and I'm still confused. Is this a mechanical guage (a tube running from the oil pressure source to the guage)? Or, is it an electrical guage (a single wire running from the sending unit to the guage)? With either unit, you still should have two more wires for the lighting of the guage (usually a red and black wire). The red (+) wire will connect to an electrical source that has 12V when the key is on, or you can connect to the headlamp wiring so that it only illuminates when the headlamps are on. The black (-) wire connects to ground. Should be able to ground it to the dash with one of the screws that are used to mount the unit (assuming a metal dash).
Loren
SW Washington
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rpacker
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Dec 13, 2008, 2:16 PM
Post #9 of 13
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Re: Oil pressure guage blowing fuses
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Yes, if you use the electrical hookup there are 4 wires (2 for the light 12v & ground) and 2 for the gauge itself (12v and the sender wire), if you use the mechanical there are 2 wires and the oil tube. I'm using the 4 wires. The lights work fine. The current state I'm at is that it seems to ground out (or it's blowing the fuse anyhow) when I use the gauge hooked up inside the car. It's screwed to the metal part beneath the radio. The gauge didn't seem to be working outside the car (I took it out of the mounting pod, those 3 gauge sets all auto parts stores sell), but it was not blowing a fuse (without the oil light sender wire hooked up). When I try it inside the car, touching the metal mounting thing to the metal part of the dash will blow the fuse.
So, does this mean there is some sort of short in the car somewhere that it's blowing the fuse when it touches the metal of the dash?
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Loren Champlain Sr
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Dec 13, 2008, 2:25 PM
Post #10 of 13
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Re: Oil pressure guage blowing fuses
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Are you trying to connect the original oil pressure sending unit wire to the aftermarket unit?
Are you saying that this aftermarket unit is both mechanical and/or electric? As if you can hook it up, either way?
You should be able to run the 12V source for the guage and the illumination from the same connection.
Loren
SW Washington
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rpacker
User
Dec 13, 2008, 2:32 PM
Post #11 of 13
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Re: Oil pressure guage blowing fuses
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No, I'm connecting a new wire to the new gauge and the new electrical sending unit. Yes, the new gauge can be either, see their pdf here: http://www.sunpro.com/publish/2004/08/05/pdf_english_16299.pdf
I do have the 12v source the same, I just split it off to the light and the gauge. Any idea why touching the metal dash with the mounting bracket blows the fuse? Also, I have a temp and volt gauge in the same cluster and they work fine. It's just the oil gauge that blows the fuse. BUT, like I said. if the oil gauge is removed from there it doesn't blow it. Okay, so could I just have a bad oil sensor?
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Loren Champlain Sr
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Dec 13, 2008, 2:49 PM
Post #12 of 13
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Re: Oil pressure guage blowing fuses
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There should be 'insulators' between the guage itself and the mounting bracket on the back of the guage that attaches the guage to the holder. If the 12V wire isn't insulated from the bracket, that could be your problem.
If everything is mounted correctly, and the wiring is okay, then I'd have to agree that it is something internal in the guage.
back of guage
+ - Where the wire attaches at (+), there has to be insulators so that the
___I_______I_____ positive post or the wire can't touch the bracket.
[ ]
[ ]bracket
[ ]
___________________
front of guage
Loren
SW Washington
(This post was edited by landdchamploren on Dec 13, 2008, 2:58 PM)
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Loren Champlain Sr
Veteran
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Dec 13, 2008, 3:00 PM
Post #13 of 13
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Re: Oil pressure guage blowing fuses
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Well, just looked at the last mssg. I sent. My 'drawing' didn't post as I 'drew' it.. Hope you can decipher what I was trying to 'say'.
Loren
SW Washington
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