Oil 'dummy' Light flickers on

[BiffWilley]

SO I just started using my 66 f100 as my daily driver. The PO told me the engine and tranny had less then 1000 miles on the build. Everything has been tight and runs really nice. I thought it was wierd but he also put in a oil pressure gage. Just the other day, the oil light on the dash started flickering. The oil pressure has been steady and good. I checked the oil and that was fine too.

Has anyone had this issue? I've had to mess with the wiper wires, and noticed most of the dash is a lil brittle, so I'm hoping/assuming that its just a bad wire.

Anyone know where a good replacement harness is. I'm completely wire dumb, but I feel like these truck shouldn't be too bad.

Thanks for the time and response!
Cheers,
Biff

[Toyz]

I would check the switch (sender) and connections before worrying about the brittle harness. If you remove and ground the wire at the pressure switch the light should be off with key on. If this proves true replace the oil pressure switch.
Paul

[BiffWilley]

sweet! Thanks for the fast response Paul. Least its somewhere to start.

[Leeroy]

Do you know what oil is in the motor?
Whilst everything should be tight, I used to run both my slick and mustang (289) on 10w40 but in summer I had a similar problem with the slick. I changed to 20w50 and never had a problem since. (That was 2 years ago)

[BiffWilley]

That is really interesting Leeroy. This might be the reason. It really only started when the weather warmed up. Might be worth trying. Thanks for your input!

Cheers,
Biff

[Toyz]

Is your gauge not hooked up or is it also not showing adequate pressure?
Paul

[BiffWilley]

So heres something new. Still haven't had a chance to check the wiring. It was been somewhat cooler these last couple of days, and BOOM the light isnt on. The pressure gauge is hooked up and still is showing good pressure. So not sure whats going on. hahah!

Thanks for all your help!
Biff

[Limestone66]

Is your gauge not hooked up or is it also not showing adequate pressure?
Paul

Could be a bad sending unit if it persists on coming on, or you could add a quart of good ol 'MMO' next time you change yer oil........................Just kidding..........Just kidding

[Toyz]

Is your gauge not hooked up or is it also not showing adequate pressure?
Paul

Could be a bad sending unit if it persists on coming on, or you could add a quart of good ol 'MMO' next time you change yer oil........................Just kidding..........Just kidding

And I was just about to suggest that
Paul

[bobenhotep]

The oil pressure light has power to it whenever there is acc power on. the sending unit turns the light on by providing a ground. The sender can be doing what you are describing, but it sounds like the wire between the sender and the light has rubbed the insulation off and is grounding. I would check the wire before I changed the sender.

[BiffWilley]

Cool COol! Once Again, I really appreciate your guys' input. I will definitely try to get out there and check her out, once I figure this thing out, I'll be sure to let you guys know.

Have a great rest of your weekend!
Biff

[Toyz]

If you wish to check the wire circuit, remove the wire from the switch terminal, tape the end of the wire, then wiggle and pull gently on the wire with key on. do the same wiggle and gently pull on the dash wiring. If this causes the light to illuminate, then you've got a intermittent short in the wire. The wire in question should be white with a red tracer. This wire should attach to the ignition switch "coil" or "ignition" terminal, then run to the light, then on in the harness to the pressure switch.
If these exercises do not cause the light to illuminate, since you have a gauge to indicate pressure; drive around with the wire still removed from pressure switch, and secured from touching ground at terminal. If the symptoms recur, then you have an intermittent short in the wiring. If the symptoms do not recur, replace the pressure switch.
Ford has done some really strange things with the pressure monitoring systems on these old trucks, so there are a couple other possibilities to be considered before replacing/repairing wiring.
Paul

[Limestone66]

No need to be replacing the oil sending unit unless you hafto. If this continues to come on, then start conducting the wire tests as described above. The way i look at it, If you were 'President', then you have a huge team of 'advisors' that will steer you in the right direction. Good luck.