Starter relay wiring - Junction Block

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Russ McElwee

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Need some visual help. Have a 71 Mach 1 project car that I did not take apart. Putting back together and have all the books and diagrams for wiring but just can't seem to figure this one out. The car has all the accessories - heated rear window, power windows and the separate Mach 1 gauges in the console. I have the proper power window/heated rear window relay and harness and know that hooks into the Junction Block next to the starter relay. But what/where does the power come from? What wire hooks the junction block up to the power Supply - direct jumper from the battery? Other power source that is not "hot" all the time? I am a visual person - so does anyone have a VERY clear picture of the actual set-up - along with written explanation would be really great. Midlife has worked the harness over (both engine and dash) but wires are still hard to read colors. Have new gauge and alternator sub-harnesses. Any help would be appreciated. Live in the Charlotte, NC area so if by chance anyone has a car with the same set-up - would love to see first hand.
 

Hemikiller

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The circuit breaker for the auxiliary power feed usually attaches to the starter solenoid. I have seen it on the terminal block as well, so either one will work as intended. IIRC, the terminal block mounted CB will have a terminal strip with a 90° bend, whereas the solenoid mounted unit will have a straight strip.

The two wires attached to the terminal block are both Black w/Orange stripe. One is the heavy gauge wire from the alternator harness, the other comes out of the main engine bay harness. The heavy solid Yellow from the main harness attaches to the starter solenoid, along with the Battery (+) cable.


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73 Grande will undergo three phase build process. Phase 1 is to make roadworthy. Phase 2 is interior/exterior restoration. Phase 3 is ++ performance.
I don’t know if this helps, but this pic shows the back with orange stripe Hemikiller described, it’s from a 1971 429 mustang site. Hope it’s helpful.

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steves73

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While we're talking about this part, is mine doing anything? Looks like it's just a normal connection because mine didn't need a break?
 

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The junction block is there for cars that had a lot of power options - like power windows, top, AC, rear defrost, convenience group, etc. They way the options were created meant there were too many spade connections that needed to be made without providing a second post. There just weren't enough threads on the original post.
 

midlife

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The junction block is there for cars that had a lot of power options - like power windows, top, AC, rear defrost, convenience group, etc. They way the options were created meant there were too many spade connections that needed to be made without providing a second post. There just weren't enough threads on the original post.
Actually, it is there to join the alternator input wire and the main power line and to allow proper wiring for the ammeter. All 7123's with ammeters have the junction block.
 
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My all time favorite vehicle is our 1969 Shelby GT500
Here attached is a PDF file with some info you may find helpful. One file is for a 1969 Mustang. But in this area the circuitry between 1969 & 1971-1973 Starter Relay systems are very similar.
 

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Hemikiller

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The junction block is there for cars that had a lot of power options - like power windows, top, AC, rear defrost, convenience group, etc. They way the options were created meant there were too many spade connections that needed to be made without providing a second post. There just weren't enough threads on the original post.

Midlife is correct, the block was primarily for the ammeter wiring, so it was common to any car with the Instrumentation Group or Mach 1 Sports Interior.

Convenience Group components were powered off the Accessory Post in the fuse box with it's triple connector yellow pigtail and pink w/orange hash wire. The rear defrost switch was connected to it as well, to switch the relay.

AC used the same fuse location as the heater-only blower motor, but with a 30A fuse.

Power windows, rear defroster grid power, power seat (Cougar only), and convertible top used the accessory power feed wire that runs across the PS shock tower brace with the CB at the solenoid.
 

midlife

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Midlife is correct, the block was primarily for the ammeter wiring, so it was common to any car with the Instrumentation Group or Mach 1 Sports Interior.

Convenience Group components were powered off the Accessory Post in the fuse box with it's triple connector yellow pigtail and pink w/orange hash wire. The rear defrost switch was connected to it as well, to switch the relay.

AC used the same fuse location as the heater-only blower motor, but with a 30A fuse.

Power windows, rear defroster grid power, power seat (Cougar only), and convertible top used the accessory power feed wire that runs across the PS shock tower brace with the CB at the solenoid.
Convenience group used both the ACC fused 3 prong plug AND the starter solenoid power feed (for the seat back release).
 
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