1976 Power Wire to Fuse Box

Josey1972

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I cant find information regarding the back of my fuse panel. I’m upgrading to a 150amp alternator in my 350 Chevota but the wire in question appears to be original.. I was told by Powermaster that I need to run a heavier guage (6) from the alternator to the fuse panel. It is a White/Blue. I pull the box and I have two of them coming into the fuse panel. I have a picture below. Can anyone tell me which one of the two is the “power wire” coming directly from the alternator? I have plugged in the battery and both of them show voltage of 12v+ with the ignition off. Appreciated.

1A4F2C70-9A5D-485E-98F0-0FF9FC93364E.jpeg
 
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Some wiring diagrams here, it just shows a wire labeled "to alternator" but it's coming off right next to the second fuse down from the top so maybe that can help

 

Josey1972

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Some wiring diagrams here, it just shows a wire labeled "to alternator" but it's coming off right next to the second fuse down from the top so maybe that can help

Thanks. I agree it does seem to be the top one and does say ”to alternator“. But I’m not sure we can trust it from that standpoint.
 

pb4ugo

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Idk if I heard of anyone doing it that way. Sounds like a lot of work. What alt are you running? Does your new alt have an internal voltage regulator? Are you still going to run power to the battery thru the stk 30 or 50 Amp ammeter?
 
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1911

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FWIW I'm running a 200-amp alternator in my (1979 build) 1980. I switched out the ammeter in the instrument cluster for a voltmeter, and upgraded my battery, starter, and alternator cables to heavier gauge, but I did not change anything in or to the fuse panel. It's been working fine that way for 11-12 years so far.
 
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I am in no way an expert in vehicle electronics. However, the way I see things is that Toyota sized the wiring based on the load for each circuit. If the load coming off the original fuse block is not changing then I don't understand why there is a need for a larger power supply wire.

If you are putting additional items in the vehicle pulling more power a secondary fuse panel would be suggested or secondary power and ground blocks to pull the power from. Most high current draw items usually recommend wiring straight to the battery and the use of heavy duty relays to handle power needs. The use of secondary power and ground blocks makes this easier.
 

Josey1972

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After doing further research I have decided not to do anything to the existing panel feed. The main reason being that I dont have any accessories running off of it. I have an Aux Blue Sea box thats wired direct to the battery for that kind of thing. I added it for that reason only. Trying to get a CB and a fridge, rock lights etc….. Plus I take pictures so I have chargers that plug in, I also have to keep a jump pack topped off etc…

I know that the PO upgraded the truck when he swapped in the 350 so he could use s 3-wire Alternator. Right now Im working on understanding how that all works.

While I’m waiting on the Powermaster I bought a cheapie replacement alternator at Autozone. Its rated at 63amps. Based on what I see the 63 isnt enough to keep up with the needs of the Dometic battery mostly. Knowing that the alternator only sends whats needed I figure I will install a ground for the unit and move forward with the project.

Thanks for the advice everyone.
 

Josey1972

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Idk if I heard of anyone doing it that way. Sounds like a lot of work. What alt are you running? Does your new alt have an internal voltage regulator? Are you still going to run power to the battery thru the stk 30 or 50 Amp ammeter?
Yes, its rated at 63 amps and is a 3 wire. The PO converted somewhere along the journey.
 

Josey1972

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I am in no way an expert in vehicle electronics. However, the way I see things is that Toyota sized the wiring based on the load for each circuit. If the load coming off the original fuse block is not changing then I don't understand why there is a need for a larger power supply wire.

If you are putting additional items in the vehicle pulling more power a secondary fuse panel would be suggested or secondary power and ground blocks to pull the power from. Most high current draw items usually recommend wiring straight to the battery and the use of heavy duty relays to handle power needs. The use of secondary power and ground blocks makes this easier.
Yes, I decided to do that originally because of the wiring being so old in the truck. I tapped the ignition for a smaller fuse block and then have a larger one running off of the battery directly. The original fuse box has been submerged a few times to I’m going to put in a CityRacer version when they become available again.
 

pb4ugo

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Im in no way an electrical expert either. You might want to check out mad electrics website for ideas on how you might want to wire it. I've never purchased anything from them, but followed some of their wiring diagrams and articles in a round about way. I also made sure the frame, engine and body all have good grounds. I run a 100+ amp older 3 wire alt. The folks your getting advice from needs to be aware the fj40 had or has an ammeter and an external voltage regulator.
 

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