79 G10 Van starter/alternator wiring issue and battery drain

[smogmuffin]

Hi all, I recently got a 79 G10 van camper conversion that has been sitting for 10 years.  I've been going over it, fixing and learning as I go.  I've got a long way to go in both areas. I was hoping someone might be able to point me in the right direction in troubleshooting a battery drain.

A few weeks ago I removed the starter to fix a frayed wire going to one of the terminals.  I removed it because I didn't really know what I was looking at and wanted a better view.

There were two red wires going to the S terminal (or at least that's how I put them back) and the I terminal is empty.  The battery cable goes where it is supposed to. Its possible that I put everything back properly, I just wanted to mention I was messing with it.

My problem is that (I suspect) my alternator is drawing 1 amp when the van is off. (measured by putting DVOM between neg cable and post) I found 12 volts at the red wire to the two wire plug going to the alternator. I'm guessing that's the sense wire.  If I unplug the sense/field connector then the draw at the battery is .15 amps.  This van has the rally gauge package so it has a voltmeter on the dash, not a dummy light.

I had the alternator rebuilt thinking the voltage regulator was bad. (a cigarette lighter volt meter also showed the voltage bouncing all over the place also)

Lo and behold the same problem exists with the rebuilt alternator. 

I've got the 79 Van service manual pdf, the haynes book and a chiltons book.  I'm just a bit too much of a novice to know where to go from here. 

Smogmuffin
1979 G10 Sportvan camper conversion.  350 with Quadrajet.  No A/C.  Power steering! 76k miles.

[zieg85]

Not an electrical expert but if it were me I would unplug the alternator to rule that out.  If that doesn't do it pull each fuse, on at a time to see if you can isolate it.  Keep us informed.  Electrical Gremlins are my least favorite issues.

[smogmuffin]

Hi Zieg,

I did unplug the alternator field/sense connector and the 1 amp drain disappears.   But since I had the alternator rebuilt, and it does the same thing I'm thinking there might be something else going on.

[hatzie]

There should only be one wire on the S terminal on your 10MT starter.  Usually it's purple.  It runs from the S terminal to the neutral safety switch and from there to the crank position on the ignition switch.

You should investigate where the extra wire goes.  It's possible that someone actually properly installed an electric fuel pump with an oil pressure safety switch that would need a "Starter is Cranking" wire.  Both of these wires should have #8-32 ring terminals so they will not fit the #10-32 R terminal that's powered when cranking.  The R terminal is present on some 10MT starter solenoids to feed the coil side of the ballast resistor on 1975 and prior breaker points ignition.  This provides full voltage to the coil while cranking...  The fuel pump safety really should be wired to this terminal with a Yellow wire, if terminal "R" is present, but the S terminal with a purple wire is just as effective.

The sense terminal in 1979 goes from regulator terminal 2 to a fusible link at the starter 3/8" BAT terminal.  It should have battery voltage all the time. 
The excite terminal should go from regulator terminal 1 through a warning lamp or a @45Ω resistance wire (on vehicles with volt gauges) to the ignition switch.  This wire should show volts with the ignition on and none with it off.
If your alternator is drawing 1A with the regulator plugged in the new regulator has a problem. 

[hatzie]

There was a brace on the tail of many 10MT starters to the block to reduce rotational stress on the starter nose, bolts, and block mounting pad.
It's extremely important to re-install the tail brace on the 27MT and 28MT diesel starters but it is possible to break bolts, crack the cast starter noses, and even crack the starter pad with the 10MT and later gear reduction starters as well.

[bd]

There should only be one wire on the S terminal on your 10MT starter.  Usually it's purple.  It runs from the S terminal to the neutral safety switch and from there to the crank position on the ignition switch.

You should investigate where the extra wire goes.  It's possible that someone actually properly installed an electric fuel pump with an oil pressure safety switch that would need a "Starter is Cranking" wire.  Both of these wires should have #8-32 ring terminals so they will not fit the #10-32 R terminal that's powered when cranking.  The R terminal is present on some 10MT starter solenoids to feed the coil side of the ballast resistor on 1975 and prior breaker points ignition.  This provides full voltage to the coil while cranking...  The fuel pump safety really should be wired to this terminal with a Yellow wire, if terminal "R" is present, but the S terminal with a purple wire is just as effective.

The sense terminal in 1979 goes from regulator terminal 2 to a fusible link at the starter 3/8" BAT terminal.  It should have battery voltage all the time. 
The excite terminal should go from regulator terminal 1 through a warning lamp or a @45Ω resistance wire (on vehicles with volt gauges) to the ignition switch.  This wire should show volts with the ignition on and none with it off.
If your alternator is drawing 1A with the regulator plugged in the new regulator has a problem.

X2

[smogmuffin]

So it looks like I misspoke when I said I had two wires to the S terminal.  One wire to the S terminal, and the other relatively thin wire with a wide loop is also on the battery terminal.  So the battery terminal on the starter has the batt cable and a thin wire.  I had forgotten that I took a video to remember how to put it back together.

Alternator shop recommends I unplug the battery cable off of the alternator and see if the draw goes away.  He said someone might have spliced a draw in to the sense/field wires and when it gets plugged in it starts to draw.  I'll poke around a bit more and let you guys know what I find tonight.

[hatzie]

Hmmm... That doesn't sound right.

If Bubba tied something into the sense wire or the J-Block it would draw current whether Sense or Charge is plugged/bolted onto the alternator or not because both wires are tied directly to the battery at the 3/8" starter BAT lug regardless of whether the alternator is plugged in or not.

Two Circuit 2 wires 2E & 2H are the main power feed at the firewall junction block to the fuse panel and ignition switch inside the cab.
The Sense wire 2G splices into the Circuit 2 fuse panel power feed wire 2H. That splice joins wires 2G & 2H to Fusible link 2B.
The alternator BAT wire 2C splices into the Circuit 2 fuse panel power feed wire 2E.  This splice also joins wires 2C, 2E, 2F, & 2K back to Fusible link 2A.

Circuit 25 is Excite (#1).

Wire 32 BLK is the Battery Positive cable.

Wires 2A & 2B are fusible links for the fuse panel and ignition main power.

Circuit 6 is Crank from the Neutral Safety Switch and Ignition Switch.

Circuit 3 is the HEI ignition power wire.

2E & 2H are not marked on this snippet.

 

[hatzie]

This purports to be the internal schematic of a 10SI alternator.

It looks very close.

[smogmuffin]

So I got home today from work, first thing I did was disconnect the battery cable from the alternators battery post, and checked for a drain on the battery.. .08 amps.  So I reconnect the battery terminal, and .08 amps again.  Disconnect/reconnect the sense and field connector and still .08 amps.  Start the van and 14.4 volts at the cigarette lighter, steady as it should be.

So I'm guessing I've still got a short somewhere, it's just not there right now.

Oh and magically the turn signal lamps work as they should now.  Before they would glow yellow with the headlights on, but the turn signal switch would not do anything.  So something was shorted with a common denominator related to all of the above.  I'll post again if I figure it out or it happens again.  With my luck, the battery will be 5V by tomorrow morning.

[hatzie]

So I got home today from work, first thing I did was disconnect the battery cable from the alternators battery post, and checked for a drain on the battery.. .08 amps.  So I reconnect the battery terminal, and .08 amps again.  Disconnect/reconnect the sense and field connector and still .08 amps.  Start the van and 14.4 volts at the cigarette lighter, steady as it should be.

So I'm guessing I've still got a short somewhere, it's just not there right now.

Oh and magically the turn signal lamps work as they should now.  Before they would glow yellow with the headlights on, but the turn signal switch would not do anything.  So something was shorted with a common denominator related to all of the above.  I'll post again if I figure it out or it happens again.  With my luck, the battery will be 5V by tomorrow morning.

The turns could be the lamp grounds.  On the CK chassis these grounds are on the radiator support.  Not sure where they are on the G chassis.  Probably the same place. 

One of the transistors in the regulator may be leaking after it gets hot. 

I have the 1979 G Van wiring diagram section.  It's only a few 12x36" pages.  I'll scan em and stitch em tomorrow or tonite.  They may help you chasing gremlins. 

The snippet above is from the 1983 diagrams.  The starter/alternator circuits didn't change but other stuff is different.

You can get hard copies on evilbay pretty cheap.  The G series vans are a section in the 1979 light truck wiring manuals.