This past weekend was the 1st weekend since finals, so I had a little bit of time to tinker with my 78 F250. I noticed that the positive cable from the battery to the starter solenoid was in terrible shape, so I decided to change it. After I changed it, I ran to the Home Depot to get some stuff and noticed the following:

Easier start-up
The oil pressure did not drop down below L (I already bought an oil pump because I thought the oil pump was bad.)
Better idle

Maybe these things are totally unrelated to changing the positive cable. I'm just trying to figure out if I should have a couple more test runs to see if the oil pressure drops before I decide not to change the oil pump. (It usually drops really low when I am sitting at a red light at an idle.)

 

You have a battery cable running from the battery to the starter???? Sure about that? There should be one cable running from the battery to the starter solenoid, and then to the starter. Without this the direct connection would engage the starter all of the time.
If you changed the cable to the starter then this cable is only responsible for the starter engagement, and does little for any oil pressure.
Though you should probably not trust you gauge to determine oil pressure. You may not even have a problem with the oil pump. Verify oil pressure with a quality gauge that can indicate the true pressure and not just the factor L and H. This might just be a sending unit problem, or some electrical issue in the wire from the sending unit to the gauge.
A mechanical gauge would be a better alternative to ensure accuracy.
A worn engine with wide bearing tolerances will have poor oil pressure, so dont be too quick to blame the oil pump.
A contaminated screen on the pick up can also cause this problem and starve the engine of oil.

 

He did the right thing...

Josh

 

The cable had 30 years of wear on it. So it's all corroded from the lead batteries.

Changing out the rest of the cables (the solenoid to starter, and the negative cable) should see some even more easier starts and brighter lights.

Upgrading to a heavier AWG will help with transfer as well.

 

I clearly stated that the cable goes from the battery to the starter solenoid. I never said the cable goes to the starter.

I am not relying solely on the oil gauge for oil pressure, but was only stating that I noticed that the gauge was not dropping at idle as it had.

 

You are right, I missed the solenoid all together. There it is all typed out for all to read. Just missed it.

You have a redundant oil pressure monitoring system? There is another gauge? Does this drop off the same amount as the factory one does too?
Mechanical gauges will be more accurate than the electric units just because it eliminates the variable of voltage drops or poor conductors.
A better connection and a better cable could have helped a number of things, especially the cable that you replaced. This cable can be responsible for a veriety of things, that may include the master power to the cab. You may have noticed that your seat belt buzzer sounds different, or the lights are brighter too.
There is a great chance that many positive (pun intended) results could have come from this preventative maintenance practice.
If the positive cable was in poor condition, there is a good chance that the negative cable also requires some attention.

 

we all have those kinds of days

 

Here are some things to consider. If both your stock oil pressure sending unit, and the aftermarket mechanical gauge are sourced from the stock sending unit fitting on the engine using a T-fitting, then ignore the stock gauge completely. At no point will the electric gauge trump the mechanical gauge. Electric gauges are slow to respond, and they introduce error into the reading because they first convert oil pressure to resistance, then read the resistance. However, the mechanical gauge literally brings the oil right up to the gauge and pushes the needle.

However, if either gauge sources from a point on the engine block other than the original factory sending unit location, then this is incorrect. The original location, by design, sources pressure from as close to the end of the oiling system as practical, so as to obtain the lowest, worst-case pressure reading. If you have installed your mechanical gauge at any other spot, this is incorrect. In this case, the mechanical gauge may give an "optimistic" reading. The difference in pressure between the two locations may or may not be negligible. To be safe, the only correct way to use two oil pressure gauges simultaneously is to install both in the same spot using a T-fitting.

If your mechanical gauge is installed in the correct spot and your oil pressure never drops below 10 pounds per 1000 RPM, then the factory electric gauge might as well speak Spanish for all you care.