Voltage Drop - common ground or power wire issues? (1 Viewer)

[coultl]

My dash voltage gauge and Sniper ECU both read low voltages, especially when the lights are on / there's more current draw. I threw parts at it because that works sometimes...not this time. Fresh alternator rebuild and new fusible link and no change. That work needed to happen anyway. The voltage gauge even dips when the blinker is on...dips at each blink. Voltage at the battery is good (newer high quality battery) but it is about a volt lower than the voltage at the alternator.

Before I go trying to find a needle in a haystack, are there common ground or power line issues on the FJ60?

All ideas are very appreciated!

 

[ToyotaMatt]

Resistance across a LOAD + FJ60 + 35+ years old = Corrosion

 

[Seth S]

anything connected to the stock wiring harness is going to see a voltage drop. Could be almost 2 volts along some of the longer pieces of the harness. Also your alternator doesn’t output it’s max amperage at idle. If you rev the engine up to maybe 1500 or 2000 you should see your voltage come up. One way to help everything out is replace your battery cables and battery terminals. Replace your main ground wires. Clean any points of contact with frame or engine etc. going to a thicker wire will help further with power on hand.

You could also go to a smaller diameter pulley on the fj60 alternator and belt accordingly. This will increase the alt rpm at idle but will also add a little more engine load because the alt will be harder to turn.

 

[OSS]

The FJ60 wiring harness was inadequate from day one. Tiny gauge wires are used throughout. What you’re seeing is the resistance through the wires & connectors.

Yes - a poor ground can cause increased resistance- and yes, all the gauge indicators ground through an inadequate tiny buss thingy located behind the instrument panel that more often than not is compromised cuz they all eventually get cooked.

 

[coultl]

Got it. So is the answer to basically to just deal with the voltage drop. I can do that...

 

[Seth S]

Got it. So is the answer to basically to just deal with the voltage drop. I can do that...

No the answer is to build better circuits with proper grounds and gage wires for the components you want/need to work properly

 

[Paullus]

I just redid my fusible links and positive battery terminal. The little bolts on the top of the OLD positive battery terminal were not tight! - they are for clamping down the starter wire and the single fusible link wire. I also had to clean the starter cable wires due to lots of green corrosion bits. Make sure everything is tight.

After doing the above, I was checking my alternator on Saturday and with partial choke at 1100 rpm the battery was reading 14.6 volts.

Once I shut everything down the battery read 12.7 volts

Also check for any loose wire ends. My side marker lights have fallen apart and the bare connectors are just flopping around so I wrapped each one in electrical tape.

 

[chriscwill07]

The FJ harness does suck but getting the health of the charge circuit right between the alternator and battery does wonders. I read 14.2 volts @ 1000 rpms and + on my voltage meter I installed in my cab. Get good battery connections, cables, good fusible links, and new wiring from the alternator and you will see excellent voltage.

 

[chriscwill07]

Got it. So is the answer to basically to just deal with the voltage drop. I can do that...

Before you throw anymore parts at it check your voltage output from the alternator. Take a meter and read your voltage on the post on the back of the alternator. It should higher than 13V. Then check your voltage at the battery terminal. Compare those two to see the voltage drop from the alt to the battery. It should not be more than 0.25V difference.

At 1000RPMs your alternator should put out close to 14V if it doesn’t you need a new alternator or your belt is way loose.

If you see a voltage drop greater than 0.25V from alt to battery your wiring is bad between there. Fusible links are a common culprit. I changed mine and that didnt fix my voltage drop problem. The problem was actually the wires coming from the alternator to the fusible link and the harness.

The alternator has one wire that puts power straight into your harness and another that goes to the battery to charge it. These wires see a lot of heat through the life of the vehicle and are moved around each time you change the alternator. I would rewire those 2. Use 8 gauge or 10 gauge wire. 10 is easier to find at your local part stores but 8 gauge would be the better bet. I rewired with 10 and have excellent voltage inside the cab and at the battery now.

 

[2mbb]

I found a voltage drop across the ignition switch. the OEM voltage meter measures the voltage after the switch and I suppose your FI computer does too. For 20 years my voltage gauge drops when the headlights come on and ticks down when the turn signals are one.

A little while ago I was noticing lower than normal voltages at the gauge. I did a little testing and replaced the voltage regular and now everything is back to "normal".

Like the OEM temperature gauge, I consider the voltage measurements to be "relative". Watch the gauge and understand what is "normal". When it appears abnormal, then you investigate for a problem.

If your FI ECU is bothered by the low voltage you may need to bring a correct size wire direct from the battery and use a relay for the ignition switch control.

 

[coultl]

Thanks for the tips. I do see a 1V drop from the alternator to the battery, so I think I'll focus there. I doubt that will get rid of the other voltage drops, but that's not really harming anything. The ECU is still over 12V and it's happy. The headlights are relayed, and I'm guessing there would be substantial drop if they were not.

 

[Seth S]

Thanks for the tips. I do see a 1V drop from the alternator to the battery, so I think I'll focus there. I doubt that will get rid of the other voltage drops, but that's not really harming anything. The ECU is still over 12V and it's happy. The headlights are relayed, and I'm guessing there would be substantial drop if they were not.

in my stock 60 harness I see a 1v drop between the battery and the headlights.

 

[chriscwill07]

Thanks for the tips. I do see a 1V drop from the alternator to the battery, so I think I'll focus there. I doubt that will get rid of the other voltage drops, but that's not really harming anything. The ECU is still over 12V and it's happy. The headlights are relayed, and I'm guessing there would be substantial drop if they were not.

That will help charging a ton. I would definitely replace both wires coming off the alternator and splice in as close to the battery as you can on one and as close as you can to the harness on the other wire. You can check voltage on the fuses also in the fuse box by putting your lead on the little metal contact on top of the fuse. If your fuse is getting the same voltage as your alternator is putting out the problem is after the fusebox… that’s when you start thinking about what you have worked on in the dash, or what components are actually getting low voltage (a little more difficult to track down). If the fuse isn’t getting the same voltage as your alt puts out then you work your way back through the circuit through the harness to the alternator and battery