1972 amp meter / Blower motor ?

[Gary G.]

The amp meter on our 72 350 A/C P/S P/B car has me wondering.
The Alternator is new. The battery is new. Grounds are all intact and clean.
When I first start the car it will read 20-30 amps. Then within a few minutes of normal operation it is back to zero. Turning on the head lamps, radio, and blower motor and it stays very close to zero (no movement that I can see). 13.8 volts when tested at the battery while running. We drove the car to Nebraska and back with no issues. Battery stayed fully charged. Normal operation? or a sign of a failing meter?
The second question. Today I turned the blower fan to high and it does not work. All other speeds work fine. Before I dig into fixinging, I thought I would ask the experts.
Thank you all in advance.
Gary & Dawn Goodyear
66059
1981 St. Louis Build restomod
1981 Bowling Green Build restoration in progress
1972 Sportsman

[Mark E.]

Re: 1972 amp meter / Blower motor ?

The behavior of the battery gauge sounds normal except for the 20-30 amp reading for a few minutes after start. I typically see a slight positive reading for a minute or two. This gauge measures voltage drop between the starter solenoid and the junction block on the horn relay. Check for tight, clean connections. Another possibility is a bad battery cell.

Regarding high-speed blower operation, check the blower relay. The service manual has a detailed diagnostic flowchart.

[Edward J.]

Re: 1972 amp meter / Blower motor ?

Gary, sometimes the red or orange wires will get hot and that will sometimes melt the plastic connector housing and swell the electrical connector. If your car has a/c there is a fuse with holder (White plastic) on drivers side wheel well. Gary to add to Marks post. If your car sits more than you drive it, the battery voltage may require a higher rate of charge on start up. A new battery does loose some charge after sitting. A fully charged battery should be 12.66 this should be checked after about a hour to loose the surface charge. A quick test for electrical connections is to turn on high blower and wiggle connections at relay.

[Richard G.]

Re: 1972 amp meter / Blower motor ?

The blower motor has two feeds. Sounds like one is defective. I think it is confusing how GM wired the blower. Never did figure out the logic.

The amp meter is feed by two positives. Yes, it's confusing but the amp gauge is really a mil-volt meter reading voltage drop.
GM did this to avoid the cost of running large wires to the gauge panel.
It is unlikely their is anything wrong with your gauge as long as it is reading something.
The high amps after starting seems normal enough. Especially with the sometimes long cranking associated with long down times.
Unsure why the amp gauge would be under reporting a draw, unless their is a big difference in draw in the two scenarios.
All the gauge leg connections have to be perfectly clean and tight for this gauge to work properly. I would pull every connection clean it and add some dialectic to keep them from corroding. I have had good luck fixing most of the gauges this way. The sensitivity of the connections to even a small increase in resistance makes this system difficult to keep it calibrated or even working. It is my belief this is the real reason GM went the voltage gauge.

You can check the gauge function by removing the wires, from the gauge, and attaching them to a volt meter. I believe full scale on the gauge is somewhat close to one volt. I would have to confirm this as it is only a best guess.

Rick

[Brad Hillhouse (37766)]

Re: 1972 amp meter / Blower motor ?

Gary - I believe there is a high speed blower relay out on the AC box that goes bad. I have also seen the wires at the relay burnt/crispy which could be the cause of the problem if the relay is ok. I have had the same situation where the 3 other speeds work on the fan but high does not work.

I can send a link to wilcox that has a nice diagram if needed.

Brad Hillhouse

[Gary G.]

Re: 1972 amp meter / Blower motor ?

Thank you all for the advice. Looking at the wire harness I am going to be replacing the entire harness. Over the years it has had modifications and its time. I will keep everyone informed as the winter months are now here and I will have more free time to work on it.