Voltage Issue
Thread Starter
Instructor
Joined: Nov 2014
Posts: 239
Likes: 116
From: Wilmington, NC
Voltage Issue
I've posted before about a fuel gauge issue in my 72 and still haven't resolved that, but one thing that became apparent in my troubleshooting is that I found that I have significantly lower voltage at my fuse block than at the battery. I charged the battery and have about 12.5 volts at the battery, while I have lower numbers at the fuse block. For example, the fuse for the instruments measures about 11.6 at the fuse block. The fuse for the radio measures about 11.8 volts. The car is not running when these measurements are taken because I have the gauge cluster removed. After I discovered this, I removed and thoroughly cleaned the frame ground from the battery with no change to the voltage. Any thoughts? I'm not very good at electric but this seems like it shouldn't drop like this. The car runs great otherwise. Thanks.
Race Director
Joined: Apr 2009
Posts: 19,294
Likes: 2,753
From: Charlotte NC
Are you touching the fuse itself ...or the terminal that is holding the fuse into the fuse panel. THIS can make a big difference due to a poor connection between the two.
You need to keep the voltage as the buss connector on your horn relay. It is getting pwoer form the stud on your starter solenoid that has the positive battery cable attached to it. IF the buss connector on the horn relay is NOT battery voltage..then you possible have dirty corroded wire attached to the positive battery cable at your solenoid.
I would be a bit more concerned on what your readings are when the engine is running.
You are basically worried about a half a volt to almost one volt. And due to wire lengths and age...and if your fuse terminals are dirty/corroded/loose...which they are well known to get like that...I would not worry too much until I know what your readings are when it is running.
For the heck of it....go do this test on your newer car and see what it shows.
DUB
You need to keep the voltage as the buss connector on your horn relay. It is getting pwoer form the stud on your starter solenoid that has the positive battery cable attached to it. IF the buss connector on the horn relay is NOT battery voltage..then you possible have dirty corroded wire attached to the positive battery cable at your solenoid.
I would be a bit more concerned on what your readings are when the engine is running.
You are basically worried about a half a volt to almost one volt. And due to wire lengths and age...and if your fuse terminals are dirty/corroded/loose...which they are well known to get like that...I would not worry too much until I know what your readings are when it is running.
For the heck of it....go do this test on your newer car and see what it shows.
DUB
5th Gear
Joined: Aug 2009
Posts: 5
Likes: 1
Opinion on Voltage levels
I would not be concerned with those voltages. There are inherant resistances that exist relative to wire length, aging connectors etc. that may have some corrosion. Its called voltage drop and completely normal.
I spent much of my 20's wiring cars BTW.
I didnt see your earlier posts, but gas guages are pretty basic. The sender is just a big variable resistor, so troubleshooting tends to be more of a search to trace and test the wire from the back to the gauge. Happy to help if you want to tell me the issue and what steps you've taken
I spent much of my 20's wiring cars BTW.
I didnt see your earlier posts, but gas guages are pretty basic. The sender is just a big variable resistor, so troubleshooting tends to be more of a search to trace and test the wire from the back to the gauge. Happy to help if you want to tell me the issue and what steps you've taken
Pro
Joined: Nov 2016
Posts: 729
Likes: 118
From: Kelowna British Columbia
Where do you have your ground when taking your reading? On battery - ? If you have a wiring diagram quite easy to follow. Believe positive battery goes to starter and then up to hon relay. Then to fuse panel? Don't think it is a problem but easy to see your voltage drop and like Dub said start it an take same readings
Thread Starter
Instructor
Joined: Nov 2014
Posts: 239
Likes: 116
From: Wilmington, NC
I've taken the readings with a ground wire connected directly to the battery terminal. I'm not running it now because the gauge cluster is out and I don't want oil shooting all over from the gauge line lol. I am going to check and clean the positive feed to the starter and horn relay as soon as I have a little time. The fuel gauge issue is erratic readings. I've followed the Willcox troubleshooting and everything checks out except that the resistor is ohms are lower than normal. The resistor has brown areas on both sides as well as a brown oily spot in the middle. I am getting a good replacement so will see how that works.
