Discovered that my HEI ignition is only getting about 11.5 volts. Traced the wire to the fuse block and found the wire spade connector just plugged into a fuse holder and still only getting 11.5 volts at the fuse box. Thinking I might just pull a new wire from the ignition switch dedicated to the HEI. The fuse box issue is concerning as it seems some of the circuits, where fuses are missing, do not have power on either side of the fuse holder. I thought the main supply wire would feed a buss that would in turn feed all the separate circuits. It is a Painless fuse box by the way. Looks like the wiring cleanup task ahead for me will be anything but painless. I guess my main question is if anyone out there wired their HEI as I am describing.

 

Are you saying the power in the whole fuse box is 11.5 volts? What is your battery voltage? Is that with the car running? You really want to be sure you have a fuse or a fusible link on any wire. You do not want to burn your rig to the ground.

There are two sides to a fuse box. The key on side and the power all times are they the same voltage?

 

Battery voltage is a little over 12 volts and just over 14 volts with the engine running. I just have something pulling power down as my voltmeter in the car reads less than 12 volts running. I really do not want to rewire the entire car but it is a real mess under the dash. I have added electric fans but they are direct wired through a switched and fused feed from the battery. I'm going to pull the ignition switch and check all the connections before anything else.

 

Do you know how to do a voltage drop test? If you put the positive lead on your voltmeter on a power source and you put the negative lead on the other end of the wire/connector/switch then look at the listed voltage. If it shows 1 volt then that is the voltage drop at that component. If you have power drop across the whole system you need to keep in mind that grounds are more likely then Positive current. Major power junctions tend to be copper and are much less likely to cause a voltage drop. The same voltage drop test works on grounds just reverse your leads. If you have a digital volt meter and you get the leads wrong it will just show as minus voltage.

So if I had 14 volts at the alternator and 11.5 volts at the fuse box you could try to track down where the voltages is dropping but I would just add a temporary ground strap from the engine to the fender and one from the battery neg terminal to the engine. If you don't have larger wire you could use smaller wire and check for a voltage drop on the temp ground straps. then see if my voltages level out.

Back when I was a GM tech and working with GM with a problem car in many cases the first thing their engineer would have me do is to add ground straps in different areas on the car and verify voltage drop. They always wanted to see Zero to .01 volts. If I did not get Zero they would say "fix that and call me back if there was still a problem".

 

I just did that test to see how much my new electric fuel pump is pulling down the voltage. I have 12 volts at the pump fuse, pump and engine not running, until I switch on the pump. With the pump running, engine not running, I have about 11.5 volts. The pump circuit does not use a relay, so maybe adding a relay will improve this issue??

 

.5 volt drop across those connection with a high load fuel pump is not that bad, But I don't think that should bring the whole fuse block down. How far does the battery drop when you turn on the fuel pump. ?

BTW do you have any symptom in the car? Any concerns? .5 volt drop is not a big deal now 14 volts to 11.5 volts is an issue. I still think its most likely ground but for a small drop like .5 volts you may just need one gage size bigger feed wire. fed. If the whole battery is dropping to 11.5V then there is no in car issue.

If you whole fuse box is dropping and you have a performance fuel pump a relay may be the fix. Just do not skimp on the relay as it is considered a safety item. The fuel pump shutting off at the wrong time can be dangerous. GM use to wire its cars so that the pump get power even if the relay fails. At least until the car shuts off, then it will not restart.