I am working on a wiring issue that Frankie has been patiently advising me on. So as not to outstay my private messaging welcome, I wanted to put my last question out to the collective.

I have a 66 vert with a L-79. She has a 42 amp alternator with a separate voltage regulator. At issue is seat heaters I am installing, each of which draw 7 amps. There is a Vintage Audio radio that is fused for 10 amps and a USP port to charge my phone. All of these will at times be on simultaneously for a total 30 amp-ish draw. To supply this current I plan to install a (6) fuse block that is activated by a continuous duty relay that is key activated. To supply the new fuse block Frank has correctly instructed me that the voltage regulator senses current draw through the horn relay and adjusts alternator output to compensate. For that and my dash gauge to work, I need to tap my new power supply there.

I have been unable to determine the wire gauge of the existing wires attached to the horn relay but I know that 30 amps requires 10 gauge, probably larger as the horn relay has existing OE loads on it. The plan would be to replace the OE wire that brings current to the relay with an appropriate gauge fused wire and then to run a 10 gauge from the horn relay to my new fuse block.

Studying the wiring diagram it is unclear to me which wire(s) supply the horn relay with current, which one I should upgrade. There are several wires off the relay but the 12R wire that goes to the alternator, the 12R that goes to the starter solenoid (which is also connected to Battery +) and then the green horn wire that shares a relationship with the 20B wire that also ends at the solenoid/battery + look to be candidates.

One or more of those are the wires are the one(s) I am looking for, I would think. Can someone shed light on this?

As an aside, the numbers appearing on the wiring diagram. They are for ID purposes or do they indicate gauge?

Thanks in advance,
Paul

 

I've rethought things and I don't think you need to upgrade the horn relay wires....if your alternator only tops out at 42 amps that is the limiting factor. The 63 standard alternator was like 35 amps and the alternator for A/C cars was 52 amps (more than yours) and the wiring was not modified at the horn relay...

I added Vintage Air A/C to my 63 with the alternator upgraded to 70 amps with power taken off the horn relay....running down the road with A/C full blast, the radio playing and high beams on is no issue...

 

Ok so if I tap that unused connector on my horn relay, run a 10g to my new panel, I have not created a potential smoke issue. Leave the OE wiring alone and get on with the project, yes?

 

Yes - and as we discussed add an appropriately sized fuse in the power feed circuit - I'd start with a 30 amp ATC blade fuse and see if that worked.

 

Good enough Frank.

 

The alternator and voltage regulator “tie point” is at the horn relay buss - that’s where the charging demands are sensed. Bypassing that will make your dash gauge inaccurate and the charging requirements incorrect.

The Mad Electric web site discusses this at length.