OK, just noticed that when I go to the far right (High) switch position, my ammeter pegs out to the right.  All the other position the needle barely moves.  I replaced the blower motor resistor, the one that fits inside the air plenum from the firewall, a couple of years ago.  Is that what is causing this?

Nope....on "High", the resistor is not even in play. The high speed blower works strictly off of the high speed relay...it's a completely separate circuit. Does the gauge ever come back down, or does it stay pegged all the time with the blower on High?
If it stays pegged, I'd have to suspect the blower motor drawing too many amps, or the connector on the high speed relay being corroded. High speed relay should be mounted on the A/C evaporator box under the hood(if it has A/C). With no A/C it would still be mounted in the same general area.




|UPDATED|9/28/2012 2:44:49 PM (AZT)|/UPDATED|

It stays pegged.  This just started happening.  I replaced the relay you show back in the early 2000's.  I'll have to check the wiring to make sure the plug hasn't fallen off.

If it's blowin, the plug hasn't fallen off, but it may be loose, corroded, or might even be melted some. It's normal for the gauge to show a dis-charge when you first turn it on high, but the alt/regulator should make up for it, and bring it back to normal fairly quickly...unless the alternator/regulator isn't up to par.

The gauge staying pegged to the "Charge" side sure leans toward the blower simply drawing too many amps, and the alternator is trying to keep the output up high enough to overcome the draw....Really sounds more like a bad blower motor to me, but it can certainly be a bad connection, too.

Does it dim the headlights when you turn it on "High"?


|UPDATED|9/28/2012 7:55:22 PM (AZT)|/UPDATED|

Like Adam's Apple said, the high speed circuit doesn't have a resistor in line.  It gets full voltage from the Orange wire that goes from the "High Speed Relay" over to the "Horn Relay" on the driver's side.  By the horn relay, there should be a fuse holder.  My '73 has a 30 amp fuse in it.  First off, see if your fuse is 30 Amp and not higher.  Then follow that orange wire from the fuse holder back to the high speed relay looking for worn off or missing insulation that might be allowing some current to flow to ground.  If everything is good, then you probably need a new blower motor.

OK, here is what I found.  The 2 wire connecter that plugs onto the resistor that is on the SIDE of the blower motor plenum was unplugged.  Not the resistor that fits into the top of the housing (just under the relay in Joel's picture), but the one that fits into the side of the housing.  I had to take the passenger side gill off to get to it.  Unfortunately, when I tried to slide the connector onto the prongs, the whole inner part fell into the plenum.   I don't know what that resistor is called as the one on top I though was the Blower Motor resistor.  I don't think I can get the part out of the plenum.  It's there until someone, not me, has to replace the evaporator.  I may be able to take the blower out and get my hand down in there....maybe.  I tried fishing a magnet in there to no avail.  Also, I'm not finding this part in the two catalogs I've looked in so far.  I don't know what it is called.

I also have an orange wire with a round rubber connector cover just dangling around the blower motor.  Don't know what that goes to either.  There is a double wire connector plugged into the blower motor housing.

Will tinker with it some more later this week.

I fished it out!!  Took the blower out and was able to get my magnet down there an get it.  It is some kind of sensor or transistor looking thingy.  It mounts right next to the cooling air tube for the blower motor.  I'll be yahooing the part number to find out what it is.

Kinda sounds like a temp sensor, from the description....hmmm.
Doubt it has anything to do with the high speed blower issue, but who knows? Got a pic, maybe? OR post the part # on it? I can search the parts manual...

Here is the part:





Here is where it goes, the hole on the left.  The hole on the right is for the blower motor cooling tube:

Sure looks like a temp sensor, to me....but why does a '72 have that? Research time!

That, my friend, is the "Ambient Temperature Switch".


It would keep the compressor from coming on, but has nothing to do with the blower, best I can tell.

I'm gunna send ya a wiring diagram for the A/C system, in case you do not have one.


|UPDATED|10/2/2012 9:53:23 AM (AZT)|/UPDATED|