I agree with Rapid Robert on this.
Current climbing with rpms is a a battery with serious problems or some sort of short. Could be in the battery, or the wires crossing or grounding, or inside the starter relay?
Load test the battery and/or put it on a slow charge if its low.
I was thinking the bad connection at the bulkhead was making it show 40amps charge. Weird thing is, I was messing with the ammeter (an old aftermarket gauge) and at one point I started it back up and it showed zero charge for a bit...then all the sudden it started showing a high charge rate again...this was while I was troubleshooting connections and right before I realized how burned up the bulkhead connector for the ammeter feed was.
I drove the truck last night with it wired up the way I modified it. Huge difference in all the electrical stuff.
I think the situation slowly got really bad and I didn't notice.
1. Headlights are much brighter now and also, the turn signals blink much faster, even the instrument cluster and signal indicator lights are brighter. The headlights are not flickering at idle while in drive now.
2. The blower motor blows stronger
3. My brake lights and taillights are brighter as well.
4. I thought my wiper motor was going out again, on low they were acting like they were going to stop on the windshield at any moment, now they are working great.
I have an msd on the truck which has it's own power supply wire so the truck has always started fine.
I understand now.
A voltemeter can not be used where an ammeter goes. Ammeters measure current running though them.
Voltmeter has very high internal resistance. It measures potential between two locations. No current flows through it.
Running the alternator output direct to the relay terminal might be useful if running a plow or winch off of the battery - and its a battery that can handle high charge rates.
One danger is no fusible link. If the alternator shorts internally - then the battery will send all the current it can down that new 10 gage wire - until it melts.
Anyway, to answer your other question, the ammeter is no longer accurate when there are two paths from the same point (starter relay) to the distribution point.
If the battery is good, then splice your alternator output to the A20 so the power flow is basically stock, but bypassing the bulkhead connector.
Then visually check over the battery feed/charge wire (S1 etc). While the battery is disconnected, use an ohmeter to see if there's connection to ground (shouldn't be, but that 40 amps indicates something is drawing current that shouldn't be)
I'm going to have the battery load tested, I just looked and it's almost three years old, a Bosch 65-750BAGM.
I'm also going to do a quick check for shorts, I also think I might wire it up so the ammeter works correctly again but the bulkhead is bypassed and then see if it still shows a high charge rate. That might tell me if the burned up connection was causing that reading.
This truck has aftermarket gauges wired up so replacing the ammeter with a voltmeter would be pretty simple. Like I said, this stuff was all in it when I bought the thing 8 years ago, the gauges are so old some of the plastic inside is dry rotted and sitting in the bottom of the gauge sight window, I think it wouldn't hurt to put a new gauge in there, ammeter or voltmeter.
If I do the voltmeter and leave the alt output going to the relay, I would wire that up so that it has a fusible link inline with the alt feed. The two wires to the ammeter could just both bolt the + side of the voltmeter correct?
