For those without a clamp on ammeter, you can also use a voltmeter: just disconnect the positive battery lead and connect the volt meter between the cable and the positive battery post. It won;t tell you how MUCH of a drain you have, like an ammeter will, but if you see voltage, something is draining the battery. If the voltage drops to zero, you have no drain happening (or you have a dead flat battery, which is not the case here).
You can just start disconnecting things to isolate them to see where the drain is coming from. When voltage drops to zero (if using the voltmeter as described) or amps drops to zero if using an ammeter, you have disconnected the offending load.
As NDT mentioned, the foot pedal operated starter switch is one possible culprit. If it loads up with crud, it's possible a conductive path has been made even when the switch is off. It may not be enough o turn the starter, but it could drain the battery over time. Another possible point of failure is the ignition switch. If I recall correctly, there is more than one pole to the switch. If that is correct, it's possible that it shuts the ignition off properly, but does not disconnect the gauges, leaving a slow continuous drain. (If your instrument cluster includes a working voltmeter, and it it does not drop to zero when the ignition switch is off, that's an indication that you may be powering your gauge cluster all the time.) However, without further troubleshooting, both of these are just shots in the dark.
Some troubleshooting tips If you have followed the stock wiring:
- Ignition switch off. Voltmeter or clamp-on ammeter connected to show whether drain is happening.
- Disconnecting wire #4 which runs from the starter to the regulator With the stock wiring, this should leave only the starter connected to the battery. If the drain is still showing, this is where your problem lies (or one of your problems, if there is more than one drain.) If there is no drain, it's probably not the starter. Reconnect wire #4 and proceed wih the next step.
- Reconnect wire #4 and disconnect wire #10 from the regulator. (#10 feeds the circuit breakers and the ignition switch from the regulator.) At this point, only the starter, the regulator, and the generator (connected through the regulator) have any connection to the battery. (Also the ammeter, if you have one - this connects via wires 8 & 9 to the regulator. NOT to be confused with the voltmeter, which connects with the rest of the instrument cluster through the ignition switch. Not all trucks have an ammeter.) If the drain is there, your likely source is in the regulator or genrator or their associated wiring (I consider the ammeter, if it exists unlikely to be the problem, but you could disconnect it to be sure.) If there is no drain, reconnect wire #10
- If you have stock wiring, all of the rest of the truck is fed by either the circuit breakers or the ignition switch. This ignition switch feeds both the ignition and the gauge cluster (NOTE the ignition switch does NOT feed the gauge cluster lights. They are fed by the circuit breaker which provides power to the light switch.) Wire #10 brings the power over from the regulator. Wire #11 connects that feed to the circuit breakers and the ignition switch. Disconnect wire #11 from the ignition switch. This cuts off all power feeding the switch. If the drain goes away with this disconnected, there are two possibilities: either the ignition itself was still powered even with the switch off (unlikely, since then your truck would keep running when the ignition switch was turned off), or the feed to the instrument cluster was still live.
- If the drain is still there, even with the ignition switch disconnected, you'll need to disconnect the various circuit breakers one at a time until you see the drain go away. The circuit that makes the drain stop when disconnected is the one you'll need to trace out to find the source of the drain.
I had a problem that my ignition switch failed in the on position (non-standard wiring, using the key ignition on the Chevy S10 steering column installed by a previous owner to energize the ignition, but still using the foot pedal for the starter). I had to bypass that with a separate toggle switch until we got around to converting back to the stock ignition set up (and an original M37 steering column)
Hope some of this helps. I wrote it off the top of my head (other than double checking the wire numbers), but I think it's accurate.
