View Single Post
Old 12-27-2016, 09:35 PM   #2
VetteVet
Msgt USAF Ret

 
VetteVet's Avatar
 
Join Date: Jan 2005
Location: Kalamazoo, Michigan
Posts: 8,703
Re: Need help, 70 GMC not charging

Quote:
Originally Posted by davem815 View Post
'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.

Name:  60GMCRegulator.jpg
Views: 184
Size:  108.2 KB
__________________
VetteVet

metallic green 67 stepside
74 corvette convertible
1965 Harley sportster
1995 Harley wide glide

Growing old is hell, but it beats the alternative.
VetteVet is offline   Reply With Quote