Need help, 70 GMC not charging

[davem815]

'70 GMC 307 with external voltage regulator and optional gauges in the dash cluster.

Truck quit charging, dies if I remove positive battery terminal
It has ran fine for a year and a half. PO replaced alternator within a year of selling truck to me. I had alternator checked at an alternator/starter shop and it tested fine. I replaced EVR. No change.

I have no voltage at F terminal of EVR with or without engine running. Amp gauge on dash points straight up (half way between D and C) with or without engine running. If I jump 12v from battery to F terminal on EVR, amp gauge goes to 3/4 Mark (toward C).

My research says F terminal should have around 3-4 volts with key on, engine off and 12-14 volts with engine running. I followed blue and Brown wires from alternator to EVR to firewall and did not see any breaks or splices.

What could cause no voltage at F terminal?

Thanks in advance for your help, Dave

[VetteVet]

Originally Posted by davem815

'70 GMC 307 with external voltage regulator and optional gauges in the dash cluster.

Truck quit charging, dies if I remove positive battery terminal
It has ran fine for a year and a half. PO replaced alternator within a year of selling truck to me. I had alternator checked at an alternator/starter shop and it tested fine. I replaced EVR. No change.

I have no voltage at F terminal of EVR with or without engine running. Amp gauge on dash points straight up (half way between D and C) with or without engine running. If I jump 12v from battery to F terminal on EVR, amp gauge goes to 3/4 Mark (toward C).

My research says F terminal should have around 3-4 volts with key on, engine off and 12-14 volts with engine running. I followed blue and Brown wires from alternator to EVR to firewall and did not see any breaks or splices.

What could cause no voltage at F terminal?

The voltage for the F terminal originates at the key switch on the accessory terminal. There should be a 24 gauge resistance wire there that shares that terminal with a 12 gauge brown wire for the fuse box accessories.The resistance wire runs down to the inside of the firewall block behind the fuse box and connects with the brown F wire which runs to the EVR.

If the key switch has 12 volts on that terminal with the switch on, then either the resistance wire is broken, it is not making contact with the brown EVR wire at the firewall block, or the brown wire (EVR) is broken between the firewall block and the external regulator.

The EVR wire should show 12 volts with key on and zero volts key off. There is no fuse for that wire and the ammeter is showing the charging voltage of the alternator compared to the battery voltage. It has nothing to do with whether the alternator or the regulator is working or not.

Thanks in advance for your help, Dave

Top center fourth wire down.

[davem815]

Thanks VetteVet, my switch is bad. The EVR wire had continuity from ignition switch to EVR. Ign Sw did not have 12V on ACC terminal in On position.

It looks like the problem was caused by a "reworking" of the wiring connector. It had 5 wire to the partial connector and 2 individual wires to the ACC and ALL terminals. The 2 individual terminals were side loading each other and the ACC terminal was loose in the ign sw.

It looks like my best option is to go to the junk yard and get a new connector with a pigtail. Hopefully I can de-pin my connector under the dash, replace the 5 good wires, then undo the splices on the 2 wires under the dash and solder on the two wires from the junkyard pigtail with the correct terminal and add them to the junk yard connector.

Anybody have any tips on de-pinning the connector, especially while under the dash?

[Wrenchbender Ret]

You can by a pigtail to replace the connecter at the back of the switch. A parts store should be able to order one for you.

[davem815]

I got the connector from the junkyard for a $1. Looks much better. Good to know part store sells them.

Now need to get a new switch.

[davem815]

VetteVet, I tried soldering new pigtail wires and terminals on the two wires (plus resistance wire) that had been previously been cut. I had no problems soldering the #12 stranded wires, but I have been unable to solder the #24 solid resistance wire. Is it some other material? A search suggested it might be tungsten?

Is there a way to solder this wire? would shortening it by about 3" be enough to affect the resistance and cause problems?

Would it be better to just get a new under dash wiring harness?

I think a bad solder joint with intermittent short could have been the reason the PO had replaced the alternator and messed with the under hood wiring between the EVR and alternator.

On my first soldering attempt, I was able to get intermittent connection. I want to fix this correctly to eliminate my charging problems.

Thanks in advance,
Dave

[VetteVet]

I think you would be fine with just a connector splice if you run the two ends into the connector side by side and crimp them into the connector and use heat shrink on the splice. Be sure to put the heat shrink on first.

Just for information, this is a 10 ohm resistance wire connected with the 12 gauge brown accessory wire so any 10 ohm resistance light or resistor will work if it is wired in series from the accessory terminal to the inside of the firewall block and continued to the engine side where the brown wire connects with it and then runs to the EVR or if you convert alternators the brown wire will run to the no. 1 terminal on the SI series alternator.

It has even been stated, that you can connect to any keyed on connection on the fuse panel with a light or resistor in series to the no. 1 terminal, and the result is the same. If you use a light you will have a visual notice when the alternator is not charging and when the light is out, the alternator will be charging.

[davem815]

Originally Posted by VetteVet

Be sure to put the heat shrink on first.

Lol, been there and done that before.

I forgot to post this weekend, but I got it fix and every thing is charging correctly. Thanks for all of your help.

Now I just have no lights (brights, dims, parking, turn signal) in the left front corner. I'm pretty sure it's a ground. There is a wire nut with all of the grounds in it from the p.o.. I probably bumped that when I was replacing the voltage regulator. That needed fixed anyhow.