72 chevota wiring help please

[pb4ugo]

Ok, 1st lets talk about the stk wiring with the Toyota alt and the external VR. The alt wh/blue wire(WL) supplies voltage to the VR and fuse box and also connects to the neg side of the Ammeter. The positive side of the ammeter white(W) wire goes to the Batt. The wiring done this way shows discharge and charge+-. So, the alt is charging the batt thru the whole wiring harness thru a long 10GA wire. This is old and antiquated and imo dangerous. Disconnecting the ammeter is not really bypassing it, because you are still charging the batt thru the W/L & W wires. .

Bypassing the ammeter/WL/W wires would be running a wire from the GM alt post directly to the batt. The GM alt has an internal VR. The GM alt needs 12v to the #2 terminal on the plug. The easiest way to get the 12v is to loop the #2 terminal to the Alt's charging post. The #1 terminal is the sensing terminal. If your going to run and idiot light then run a wire from the #1 terminal to the light and hook the light to a source that's hot when the key is on or install a diode. I did what @pgbottle did in post #30 and used my brake light as an idiot light. My fuse box gets its power using the white wire with the fusible link hooked to the battery.

Below is how I hooked my GM alt on a 75 40. I disconnected the ammeter and connected those 2 wires together and made sure that connection can't be grounded. I have a 6ga wire going from the alt post to the batt +. The alt's plug has the #2 terminal wire/red wire looped to the alt post. The alt's plug #1 terminal/ blue wire goes to the idiot light. That lights 2nd wire makes a connection to a source that is hot when thr key is on. The single red wire on the batts + nut post connects to the white wire/fusible link feeding the fuse box. I followed the White/Blue into the harness a bit and terminated it with a butt connecter on the end of it, so it can't be accidently grounded because it's hot. I also taped up the end, then wrapped it into the harness.

 

[franklin40]

THANK YOU!! YOU ARE AWESOME. thank makes so much more sense and i’m reading stuff outside this thread tom trying to get my head wrapped around this!! i think i’m finally getting the idea here. i now understand “bypassing” the amp meter as some threads talk about physically connecting the blue white wire behind the dash which makes me think well it needs to be in the mix here some where. your last two posts have given me so much more understanding and hope i’ll be able to sort this out as soon a i buy some 6 gauge wire and connectors!! you’re confirmation that the white blue is not needed clears things up for me soooo much! again thanks for your patience.

 

[pb4ugo]

You'll just be disconnecting the ammeter and connect those 2 wires together(WL&W). I used a small nut & bolt and nut and a bunch of tape.

 

[texcwa]

You'll just be disconnecting the ammeter and connect those 2 wires together(WL&W). I used a small nut & bolt and nut and a bunch of tape.

I did the same by just bolting the two wires together, taping and a piece of shrink tube. I also read you could just undo one of the wires off ammeter and just attach it to the same post the other wire is connected to ammeter thus no power running through the ammeter. Whatever you decide, remove the ammeter out of the wiring and run the alt directly to battery) as everyone has said. The wire that went from alt to ammeter will not be used (just tape it off since it will have power in it), and make sure you have the fusible link in the white wire running to battery (since this wire will now still supply power to the ignition switch and fuse block) but will no longer have the amperage draw from the alternator to the battery (this is the ultimate goal in the wiring).

 

[texcwa]

The below wiring diagrams are what I worked off of. The first one shows the schematic where I was verifying the wire colors, the wire colors that are circled were verified to be the same as in my 72. The second diagram shows the bypass of the ammeter. The blue wire (actually the white wire with purple or blue stripe) that has the x's through it is no longer used. The red wire (actually the white in schematic) needs to be fusible). converting from pdf to jpeg so to attach to this post makes them a bit blurry but if you want you can pm me with an email address and I can send a clean pdf that's readable.

 

[pb4ugo]

I need to ad the GM alt plug with pigtails is available at most a/p stores in their electronic section. If your idle is low upon start up the light may still stay on, a little rpm will turn it off. That's normal. If you decide to not use the sensing/terminal #1 wire the alt still should work, it just needs more rpms to excite the alt to charge. You'll hear the alt engage with a high pitch normal hummm. Don't forget to disconnect the VR.

 

[pb4ugo]

@franklin40 , I have to make a correction. The idiot light is NOT to be grounded. You'll have the alt #1 terminal wire going to the light. Instead of grounding the light it needs to be connected to a source that is hot when the ING/ key is On/hot. The light turns on when the key is turned to the on position. Once the alt is charging the light will go out.

 

[franklin40]

cheers. that’s what i thought as the exciter needs ign on power. i’m going to wire it as you’ve described using a three wire system. i’ll use my brake light too! i like that idea a lot. i assume you just don’t have the brake light wires hooked to anything? just leave that circuit open?

i think the VR has been removed but just to be sure is it on the fire wall on a 1972? i’m assuming it’ll be similar to my 1977.