Question for the electrical experts

[John4337]

Ever since I've gotten on the road, I've been chasing a small electrical gremlin. When I run my A/C, or headlights, my fuel gauge would drop. I recently put in a new oil pressure sender and the condition has worsened, now if I turn on the A/C, or headlights, my oil pressure reading goes up and my fuel level goes down. All my gauges are grounded with a Ron Francis grounding bar directly to the battery, so I'm guessing it's not a gauge issue. Any thoughts on where to begin?

[MB750]

AC and headlights are higher amperage draw than a fuel level or oil pressure gauge. Have you measured your voltage at these meters during this test? You might have voltage drop.

Also, what size wire did you use for the gauges? Too small wire (or not automotive grade or bad terminal connections) can cause voltage drop as well.

[Rdone585]

As MB750 indicated, wire gauge and bad connections are often the issue. Any connections to the frame must be to bare metal, paint is an insulator. Sometimes those crimp on connectors just don't get connected as good as you might think. Any wire splices I did were soldered and heat shrink protected. Do the gauges change if you rev the motor? Is your battery fully charged?

[Jeff33Ford]

Definitely sounds like a connection issue. Both of the gauges you mentioned work off of resistance for a reading. So that means for them to change either the resistance changes or the voltage changes. Not likely the resistance on the gauge sender causing an issue. As suggested you will find it quicker using a meter and looking for the voltage drop. In my experience it is usually a ground issue. As the current increases when using the lights or AC a bad ground will in increase in resistance which is why your gauges change in reading. I have cheated before and just temp hookup a bunch of grounds everywhere to the battery and see if the issue goes away. Then track down from there.

[John4337]

The wiring for the gauges is what FFR, Speedhut sent. I did add the grounding bar behind the dash. RPM doesn’t seem to have any effect. I was surprised that the lights had an impact as they are all LED. Battery is charged. Sounds like I’ll run some temp grounds and work from there.

[MB750]

The wiring for the gauges is what FFR, Speedhut sent. I did add the grounding bar behind the dash. RPM doesn’t seem to have any effect. I was surprised that the lights had an impact as they are all LED. Battery is charged. Sounds like I’ll run some temp grounds and work from there.

I'm not trying to be negative here (lol, yuk yuk...), but why do you think temporary grounds are a good troubleshooting technique?

[Nigel Allen]

If a temporary ground corrects the fault, then the issue is identified and easier to track down. This is especially helpful for guys with less experience or measuring tools. Many find interpreting the readings from meters very difficult.

Also worth noting, is that there is nothing so permanent as a temporary solution.:)

Cheers,

Nigel

[MB750]

If a temporary ground corrects the fault, then the issue is identified and easier to track down. This is especially helpful for guys with less experience or measuring tools. Many find interpreting the readings from meters very difficult.

Also worth noting, is that there is nothing so permanent as a temporary solution.:)

Cheers,

Nigel

That's a very good point. Sometimes I take for granted my Dad was an electrical contractor who taught me circuits during Sesame Street commercial breaks (or any skit with Snuffleupagus) so using a meter was my first go-to tool for electrical troubleshooting.

[John4337]

If a temporary ground corrects the fault, then the issue is identified and easier to track down. This is especially helpful for guys with less experience or measuring tools. Many find interpreting the readings from meters very difficult.

Also worth noting, is that there is nothing so permanent as a temporary solution.:)

Cheers,

Nigel

That's me, I find electrical mostly voodoo and witchcraft. I figured a temp ground is as good a place as any.

[Jeff33Ford]

I'm not trying to be negative here (lol, yuk yuk...), but why do you think temporary grounds are a good troubleshooting technique?

Like mentioned it is easy. If you want to start with a meter as an easy test. Hook your voltmeter to your negative battery post and the positive lead to your grounding block. Set it on a low voltage level. Then go through your routine to make the gauges go crazy and look for a voltage on the meter. If you get a voltage reading you have a grounding issue. Then repeat at several ground locations if you have others.
Edit: Don't forget to check engine grounds.

[Cobradavid]

Where is your battery mounted (trunk or front?) and what gauge battery cable to you have? Also, how old is the battery?

While I didn't have any drops in the fuel level or oil pressure needles, I would see drops in the voltage gauge when adding more powered items (lights, defroster, footbox blower). Things improved when I moved my battery to the front (Breeze battery mount is great!) and went to larger gauge battery cables.

David

[John4337]

Where is your battery mounted (trunk or front?) and what gauge battery cable to you have? Also, how old is the battery?

While I didn't have any drops in the fuel level or oil pressure needles, I would see drops in the voltage gauge when adding more powered items (lights, defroster, footbox blower). Things improved when I moved my battery to the front (Breeze battery mount is great!) and went to larger gauge battery cables.

David

I have the Breeze front mount, fairly new battery, reading 13v. I'm trying to check some of the recommendations here, but I didn't have the foresight to make my dash removable, so I can't get to some of them. ugh. This has me really confused. The fuel drop has always been there, but this oil pressure thing started with the new sender. I may get frustrated enough to swap the old one back in.