Current draw need help

[Jaysonb]

I have been getting my 80 c10 in good enough shape to drive for the rest of the fall. I put a new battery in it, and in a few days it was dead, I charged it up, same thing a few days latter. I got the meter out, and found a .9 amp draw, and narrowed it down to the heater circuit. It seems to have 12 volts going to it with the key off, looking at the wiring diagram I dont think that it should. So I just put in a new ignition switch, and there is still power going to the heater circuit with the key off. This is a non ac truck. It seems like a pretty simple circuit. Any ideas???

[bmchevy1979]

There should be a power wire going from the junction block on firewall to the relay by the blower motor disconnect that wire and see if it still has draw with your meter

[Jaysonb]

I think that the wire from the junction block to the relay by the blower is only in trucks with ac.

[bmchevy1979]

That's possible I don't have a diagram in front of me but there is a feed from fusebox to controls I believe it is a Brown wire and there is a connector in wiring harness behind gauge cluster but it is an ignition feed only on when key is in run position trace this wire and see if itis getting power when off also are you sure your key is retracting all the way to off position will it go into accessory switch may be out of adjustment

[chengny]

narrowed it down to the heater circuit. It seems to have 12 volts going to it with the key off, looking at the wiring diagram I dont think that it should.

You're right, it shouldn't. The bank of the fuse block that supplies power to the heater blower circuit (also power windows and auxiliary heater blower - if so equipped) is ignition switched and should only be hot when the key is in the RUN position. The 3 ORN-300B lead should not show 12 VDC when the key is in any other position not even ACC - and certainly not in the OFF position.





Pull the heater fuse and probe the clips on both sides.

There should only be power available on the line side (LH clip when looking at the fuse block) and that is only when the key is in RUN. Power on the line side with the key OFF would suggest a short somewhere in the column to fuse block harness.

There should never be power on the load side clip (regardless of key position). If there is power on the load side, that would indicate a short somewhere in the wiring behind the fuse block or in the 2 BRN-50 lead that feeds the blower speed switch and the resistor stack.

There is another way that the heater blower circuit can see battery power. Do you have gauges or a base package instrument panel?

If you have the base IP (and the alternator has internal problem), the battery can be connected directly to the 2 BRN-50 heater blower supply lead even when the key is off.

It can connect like this:

The 1 BRN-25 lead goes from the alternator to the GEN warning lamp on the dash. Through the lamp and then into the .5 ORN-939 lead. The ORN-393 is spliced into the BRN-50 at a connector located near the blower speed switch. Here are the essential parts of the schematic:

Battery through alternator:



From alternator, through warning lamp and out of IP:



From IP and into heater blower supply circuit:



I tried my best on the tracer colors but I am extremely color deficient.

[Jaysonb]

Thanks guys. I'm not sure how, but the new alternator I put in was bad, and somehow let current get to the heater circuit??? The alternator charged fine, but there was 12 volts at both of the terminals on the plug. I put the old alternator back in, and everything is fine.