electrical blackout woes

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powerwaggin

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I no longer own an A-body (had a '69 273 Dart) but now run a '72 W200 plow truck with 318 and 727. Everything is basically un-molested original Mopar except for a homemade HEI conversion (many thanks to this forum). After experiencing occasional complete blackouts of the wiring harness, I now run a dedicated ignition circuit fed by a fused toggle switch right off the relay post. The starter is still cranked via the original key switch on the column.
The other night, I plowing out my drive and neighbors and on the last nudge she blacked out completely. Kept running but no lights, heater, or anything. Once this happens the starter will only work by screwdriver jumping the relay on the inner fender. I parked it for the night and by morning everything worked fine again.

I have replaced all chassis/engine/body grounds thinking that might be the problem but no luck. Does this sound like the old AMP gauge issue? A bum key switch? Where do I test for key switch current?
Thanks
 

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Good firewall connections from the alternator back to the gauge, and from the battery to the other side of the gauge? No green connectors going thru the firewall? That's usually the issue. If it ain't that, I'd suspect the key switch.
 
This morning I took apart the firewall connector that includes the biggest red wire right off the starter relay (the one with a fusible link) and voila! Once I cleaned both sides of the firewall connector with electrical parts cleaner and a wire brush and pushed it all back together everything was back to normal. I will definitely bypass this connection with a big heavy gauge red wire and do the AMP gauge bypass to boot. Unfortunately the plastic locking clips are both now snapped off so the connector is just hanging there….but I'm thinking it will probably still work fine as long as I bypass the main feed wire. Thanks guys for the helpful tips….once again it comes down to me getting off my butt and trying something instead of whining!
On my retired 73 Sno-Fiter (now a parts rig only) after numerous small fuse box fires and red-neck quick fixes, I gave up on the stock harness and ran a bare bones 4 circuit panel in the glove box…..ignition, heater blower, headlights and taillights. The 72 is registered and road worthy and too clean for me to start butchering (yet)! I do now keep a fire extinguisher in the cab!
 
I've worked on 3 different pickups (back in the '80s) with electric Meyer plow hoists. All three had melted ammeters which looked like the photo on the MAD page, and damaged bulkhead connections. This was before Al Gore invented the internet.
 
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