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I have an '81. The fuse box is maxed out with things that I have added to the car (electric fuel pump etc). I've got what I think is an electrical fire waiting to happen. Too many additional feeds off of the factory fuse box imo.
I have decided to add an additional eight fuse box for the switched items that need power in the "run" position. I do not want to run the power to the new box off of an "ign" terminal at the factory fuse block.
I would like to run a large gauge (#6 or #8) supply wire from a switched source to the new box. Where can I get a switched 12v source for the new box? Is there a terminal on the starter that I can hook up to?
I think your best bet would be to install a new power relay in the car along with a new fuse block for other add-ons. Power that relay with a line coming from the ignition switch so that the relay will turn on with the ignition. Feed the power to the relay with a new line directly from the battery. It should have a main circuit breaker that is appropriately sized for whatever is going to be drawn from it (maybe twice the capacity of the fuses it services).
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
Hi,
Just use a relay. Run one wire from the battery lug on the solenoid to the relay and another heavy wire from the relay to your new fuse box,
Then trigger the relay to go on when you turn the key to ON.
Ignition power (IGN) comes directly from the ignition switch so there's no "unlimited" source of additional power. You can though use a SPST or SPDT relay (properly rated for your anticipated load). Just power the relay coil with an existing IGN power source. Run your new main power wire from the alternator (I HIGHLY suggest including a fusible link near the alternator) to one of the contacts (SPST relay) or the common contact (SPDT relay) with the other contact (SPST relay) or the NO contact (normally open SPDT relay).
I suggest running your main power wire to the alternator because such avoids taxing the wiring between the alternator and starter. With the need for so much more power I hope that you've installed a significantly higher capacity alternator.
While you make the connection for your new fuse box at the starter (solenoid) or battery, I still suggest that you make it at the alternator. Why? Because the only output wire is a ignition single 12 gauge that runs between the alternator and the starter. If you connect to the alternator your new IGN power source has direct access to alternator power without adding to the load on the wire that runs between the alternator and starter.
Okay guys a relay sounds great. The new fuse block is rated at 100 amps total. Now I will need some suggestions on a relay that will work. Do I need a high amperage relay ie 100 amp. I am not an electrical type guy but by golly I can hook up and solder. Thanks for the responses so far!
While you make the connection for your new fuse box at the starter (solenoid) or battery, I still suggest that you make it at the alternator. Why? Because the only output wire is a ignition single 12 gauge that runs between the alternator and the starter. If you connect to the alternator your new IGN power source has direct access to alternator power without adding to the load on the wire that runs between the alternator and starter.
I have added an 0/1 wire from the alternator to the starter and to the battery. I also have added an 0/1 wire in place of the factory battery cable from the battery to the starter.
With the need for so much more power I hope that you've installed a significantly higher capacity alternator.
I have a 100 amp Powermaster alternator that has been working flawlessly. Do you think that it should be upgraded to a higher output ie a 140 amp or higher?
I have a 100 amp Powermaster alternator that has been working flawlessly. Do you think that it should be upgraded to a higher output ie a 140 amp or higher?
What kind of accessories have you added? How much current do they draw? Be aware that the suggested fuse size for an electrical device is often much higher than its steady power requirement as the starting power is far more than the operating power.
I believe that the original alternator in 1981 was 70A so I would say that if your added accessories routinely draw more than 30A then you should get a higher capacity alternator.
Okay guys a relay sounds great. The new fuse block is rated at 100 amps total. Now I will need some suggestions on a relay that will work. Do I need a high amperage relay ie 100 amp. I am not an electrical type guy but by golly I can hook up and solder. Thanks for the responses so far!
While I won't say to get this exact relay, something similar to this will be easy to install and certainly adequate. Note the heavy-duty lug connectors for the power.
Unless your main wire feed length is more than say 6' (unlikely in a Corvette) you definitely don't need a wire larger than 8 gauge. You MUST however add additional protection in the form of either a fusible link (I'd honestly suggest 18 gauge unless your power requirements are extreme) or a Maxi fuse at 60A
I have added an 0/1 wire from the alternator to the starter and to the battery. I also have added an 0/1 wire in place of the factory battery cable from the battery to the starter.
Then make your power connection based upon ease of running the wire!
I have added some additional gauges, electric fuel pump, shift light, larger stereo amp. I don't think anything pulls much amperage except the amp.
You need to take a step back. Gauges and small lamps are inconsequential if you power them from a fuse box ignition connection.
I'm having a hard time thinking of any decent automotive audio amplifier that doesn't include a "remote turn-on input"--essentially a relay. Just run the main power to the amp (fused of course) from battery, alternator, starter as most convenient for you as you've already GREATLY improved the main wiring.
Ok fellas I think I've got it now. Reading your posts and doing some internet searching has given me a pretty good idea of what I want to do.
I found a similar relay to the one SwampeastMike suggested on Amazon. They also have an inline fuse holder for the larger amperage and larger wire size.
I'll use one of the switched ignition connections at the original fuse box to trigger the relay. The relay will then send power to the new fuse box.
Am I on the right track or am I missing something?
Here's a diagram I put together a while back for a fuel pump.
NOW when you are connecting up the ignition source- you have "two" ignitions- one is "on" w/ "acc" and "run" but NOT during start- you would NOT want to connect your fuel pump relay to this one. The other ignition is on during "run" and "start" but not "acc."
Here's what I used- switched the relay/fuse holder and used the ignition switch for my source- less than $10/each.
DO spend the extra money on a quality relay- I still am able to find NOS Bosch ones on eBay. Now made by Tyco
wiring at ignition switch (Verify as this is for an early shark)
I replaced my whole fuse box w/ there relay/fuse modules-
I secured the new fuse panel to the firewall below the steering column in the engine compartment.
Mounted the relay the same way. Ran the 8ga power wire to the relay from a 100 amp fused supply at the alternator.
The fuse box is supplied by 8ga from the relay. Made a ground off the relay to the frame with 8ga wire.
This is the start of the project. That's as far as it's gotten.
The switch wire has to be run from the car's fuse box to the relay next. I was planning on using 10ga wire there.
Then I start sorting out the temporary connections on the car's fuse box. That means pulling the front seat to gain access. Eventually each accessory will be wired to the additional fuse box.
I'm no electrician so I tend to use heavy gauge wire and soldered copper terminals.
What you are doing is fine...as long as the total current for the new panel does not exceed more than about 30 amps. You must remember that power input line (12vdc) to the factory supplied fuse block is only capable of a current load for the total output of that fuse block (plus a 50% safety factor). If the new fuse block can handle another 40 amps (or more) and you 'feed' it from your existing fuse block, the main power wire to the original fuse block needs to be beefed-up to handle the total load. OR, you can just run a new power wire (of adequate size)from the battery to the new fuse block [with a circuit breaker before the block].
Either way will work. But if you have added load of more than 30 amps you need to decide HOW to input that additional current to your electrical system.
What you are doing is fine...as long as the total current for the new panel does not exceed more than about 30 amps. You must remember that power input line (12vdc) to the factory supplied fuse block is only capable of a current load for the total output of that fuse block (plus a 50% safety factor). If the new fuse block can handle another 40 amps (or more) and you 'feed' it from your existing fuse block, the main power wire to the original fuse block needs to be beefed-up to handle the total load. OR, you can just run a new power wire (of adequate size)from the battery to the new fuse block [with a circuit breaker before the block].
Either way will work. But if you have added load of more than 30 amps you need to decide HOW to input that additional current to your electrical system.
I would rather beef up the supply wire to the factory fuse box to handle the total load.
I guess I locate the power wire into the fuse box and increase it's size?
How hard will that be to do?
What's entailed in replacing the wire?
Last edited by Street Rat; Oct 4, 2016 at 06:52 PM.
Reason: add question
Switched ignition source besides fuse box?
