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Guys - As said in another thread, I'm resto-mod'ing Dad's 81 F150. One of the things I'm doing is to install a 3G alternator and a power distribution box from a 97/98 F150. I think I'm just about "there" on getting the wiring planned out, but need some help. I'm going to attach a diagram, but it is somewhat busy so I'll explain what is there, along with some questions:
RELAYS
Headlight Relays: Two of the Bosch relays are to be used, one for the highs and one for the lows. They will be pulled in by the existing headlight wiring, which conveniently goes right by the location for the power dist box.
Blower Motor: The third Bosch relay will control this and will be pulled in by the existing power to the blower motor. I'll break into the wiring at the blower motor itself and run these wires with the others in a bundle.
Key On: This will be a micro-relay and it will provide power to the voltmeter that Rocketman made out of the ammeter. And it will be pulled in by the switched-power wire that goes to the existing regulator.
Choke: This will power the choke's heating element and it'll be pulled in by the stator voltage from the 3G, which is available externally in the harness.
FUSES/BREAKERS
Main Power: This will replace the one fusible link that goes from the solenoid to the main power supply for the truck. It will be a Maxi-fuse, but the size has yet to be determined - see below.
High Beams: The highs and lows will be powered either by a Maxi-fuse or cycling breakers. I haven't decided but would like your input.
Low Beams: Ditto Highs
Blower Motor: A 30A Maxi-fuse
Choke: A small Micro-fuse
Key On: A small Micro-fuse
Sub-Woofer: 20A Micro-fuse
I embeded one question above, but want to spell another out explicitly. I'm confused as to how to fuse when replacing a fusible link. The rule-of-thumb I've read says to go two sizes of wire smaller for a fusible link, and the link on these trucks (J) is 16ga for the standard alternator. That would mean that the main wire should be a 12ga, and this site says a 12ga wire is good for 20 to 25 amps. But I would think that is far too small for these trucks, and would have thought it would be more like 50 amps.
I realize that I need to break into a wiring harness and measure the actual yellow wire that feeds things, but I am looking for your input, thoughts, and guidance. However, please don't limit that to the two stated questions as I'll take input on any part of this. Thanks in advance!
1. The maxi fuse from the alternator to the battery I would think needs to be around 150amps or so. You are using a 130 amp alternator correct? I don't know if you are going to run a different belt setup, but if you did, the alternator could continuously output 130 amps. Of course if your reasons for using the 3g are something else and you only are going to run one v-belt to it, probably a 130 amp fuse would work. I would stay at least 20 amps above what your projected draw would be to prevent nuisance fuse blowing. Be warned a dead battery is going to draw what it can from the alternator.
2. On the circuit breaker versus fuses for the headlights, in the old days I would have quickly said circuit breakers. The factory seemed to always use them on the headlight circuits, I suppose since they are so important at night. But now they do use fuses for these circuits in the newer trucks, so in Rome do as the Romans do. If you look at some of the newer diagrams, they sometimes use one fuse each for the high beams, and run the lowbeams off one fuse, or the other way around. Not sure of the theory there myself.
Thanks, Dave. I should have explained a bit further on the alternator and Mega fuse. I'm thinking of installing the 160 amp capable diodes when I rebuild the 3G. I realize that just means the alternator can put out that much w/o melting the diodes, but from what I've read the 130 amp 3G is capable of throwing that much and the diodes are the limiting factor. And, I'm going to run two belts to it - the standard alternator belt and then the A/C belt with an idler running on the back of the belt to get plenty of wrap on both the compressor and the alternator. But, even then I'm wondering about using a load response control regulator. What are your thoughts about that?
As for the megafuse, I'll use the 175 amp unit that came with the Taurus box. And that seems to roughly fit your guidelines of 20 amps over the alternator's capability.
No comment on the size of fuse to replace the fusible link?
From what I understand the fancy regulators bring the alternator in at a slower rate to prevent belt squealing? Am I right on that?
For the old main fusible link, are you going to move your old yellow feed wires to the new fuse box? I would. I would run a short 4 gauge wire from the original starter relay to the new fuse box (to the 175amp fuse) and then use one of the other fuse spots to run the old yellow wires. Your taking the blower motor load off the original wiring, as well as the headlights. I would think running off a 60 amp maxi fuse would be plenty, and it still would blow if one of these wires shorted out.
The load response control (LRC) regulators apparently bring the alternator in at a controlled rate rather than immediately. I've seen specs of 40%/second, which would give full tilt in 2.5 seconds. And I've seen some rated as "10 seconds" so I assume that means 10%/second. Some say the LRC regulators are intended for small engines and that with a large engine you don't need them. But I can't see a downside to one, especially one that will bring it in at 40%/second, and see an advantage that it would ease the transition and probably reduce belt squeal. Does that make sense?
And yes, moving the yellow wire to the new box is the plan. I just need to figure out what size fuse to use. I agree 60 seems about right, but will pull the donor harness off the shelf and cut into it to find out how big the yellow wire actually is. But I only have one yellow wire, with a fusible link off the solenoid and then the wire picking up from there. But, that wire feeds to two more fusible links which are closer to the blower motor. Should I tap in back there and supply both circuits via their own, smaller capacity, fuse?
If one of your goals is to get rid of as many fusible links as you can, then yes you could bring the others back to the new fuse box. I want to say one of them might be the headlights(black red?), not sure what the other one would be without looking at the diagrams. Of course you are re-wiring the headlights so it would be hardly any load on the original headlight feed wire.
You know, if the engine is in good tune and starts right up, and you do not sit around draining the battery for long periods with the engine off, I doubt you will see much benefit from the different regulator. If your use will be different, with camper batteries, isolators, etc, then there may be a large load present when the engine is first started and there may be a benefit.
Dave - Attached are two pages from the 81 EVTM. And I've indicated what I figured out today - the yellow wire is a #10 and the BK/O is a #12. And, that fits perfectly with the rule that a fusible link should be two sizes smaller since they are #14 & #16 respectively.
This link from StangNet says that a #10 is good for 30 - 40 amps and that a #12 is good for 20 - 25 amps. But, that's not really very accurate since a lot of things go into determining what current a wire can safely carry, and part of that is the length of the run. This link from Tessco takes that into account, and confuses things greatly.
So, what fuses to use? You are right that I'm rewiring the headlights, so all that will be carried on the Bk/O wire will be:
Cigar lighter, which will actually be a 12v power port, and power door locks - 30A
Horn & cruise control 20A
Parking lights - fused at 15A
Dome, courtesy, and cargo lights - fused at 15A
It wouldn't make sense to fuse it at less than a subsequent fuse, which is 30A. But, it would be easy to have the parking lights on and open the door, bringing the dome etc lights on. So, I'm thinking maybe a 40 or 50A? And that last site says a #12 is good for 50 amp on a 10' run.
As for the yellow wire, that's the main fuse block feed. But the big current hog is the blower motor and it'll no longer be on that block. So, maybe a 50A for it as well? The wiring should be good for that.
Here's a sticky at the top of the elec forum that a guy posted that has a lot of good info. It's rather complicated, but it does have some charts with amperage ratings. The 16=10amps, 14=15amps, 12=20amps, 10=30amps, 8=40amps, etc are NEC electrical rules for structural(house) wiring. I use it since I have it in my head, and I know it will work ok with very little voltage drop. But if you are going to try and interpret what the factory used, you will need to use one of those charts and the rules in this thread. https://www.ford-trucks.com/forums/1...-and-type.html
One of those charts says a #10 is good for 50 outside the engine compartment, or 40amps inside the engine compartment.
Dave - Thanks for the link. I'd actually found that and tried to download that chart but the link is broken. So, I squinted at the chart on-screen and came to the same conclusion you did - the old saw of #14 is good for 15 amps doesn't work on a vehicle. (I know that drill too.) It certainly isn't a simple subject and the answers are quite complex as the insulation, operating environment, bundle or not, and the length of the run all come into play.
So, I'm thinking that a 40 amp fuse on the Bk/O wire and a 50 on the yellow wire is about right. And I'm thinking I'll use wire from this extra harness I have to match the colors and insulation up perfectly.
Thanks for telling me about that link being dead. I "think" I fixed it for now. It's here Coleman Cable - Literature and then click on "Industrial Catalog.... LT500" pdf.
Thanks for fixing that link. It works, but it takes a bit of reading to find exactly the info needed. I have and, armed with that, will check out the insulation on the Y and Bk/O wires to see if I can determine what they are - which should be possible due to the differing thicknesses shown. Then I'll know what the max amperage is and feel more confident in selecting fuses.
My plan is to use the same wire from my donor harness to extend things to the new power distribution box so there will be no question about the viability of the wire itself.
Guys - Here's an update on my plans. I modified the wiring diagram to make the following changes. And, I "printed" it to a "legal" size. We'll see if it is more legible - please let me know if that's a better size. I need to figure out how large to get it so it is legible as I'm hoping that these drawings can help others - but not if they can't read them.
Changes:
Low Beams: These power distribution boxes have 3 of the large Bosch-style and 3 of the smaller relays in them. By adding the Start relay instead of using a solenoid I needed to use the larger relay position that had been allotted to the Low Beams. However, since they are 55W bulbs that's really only 8 amps for the two of them and the smaller relay, which is good for 20 amps, is quite adequate.
Start: Added this relay in place of the solenoid. This will be a high-current (70A) unit so should handle the current quite adequately since Jim's test sheet shows the top of the range is only 45 amps.
Blower Motor: Moved the blower motor's relay to the bottom left to allow a better "physical" layout with the wires going back down the harness being grouped together.
So another question to y'all is what more documentation is needed to allow others to follow in my footsteps? I'm too close to this so am probably missing huge gaps. Help?
I saw your other thread about the start relay. What is driving this relay change?
The old relay handled the current of the starter, and was a connection point for power distribution. If you are using a different starter that does not need a relay, and you are now using this fuse box for the power distribution, do you need a start relay? The ignition switch and neutral start switch and the wiring can certainly handle the current of your new solenoid on the starter.
Dave - I'm going with a 460 PMGR starter, for several reasons. First, with 10.5:1 compression ratio I can use the extra torque. Second, I like the weight reduction. Third, they work better with headers.
Since the PMGR has the internal solenoid I'd like to get rid of the fender-mounted one. One reason is it'll clean things up. Another is that it makes hot-wiring it much more difficult. So, I've been researching how much current the solenoid on the PMGR draws. Jim/ArdWrknTrk posted the test results done by the manufacturer on the starter for his truck. It shows that the range of acceptable pull-in current is 25 to 45 amps, and his took 42 amps. Given that I'm not comfortable running that through the ignition switch. In fact, I'm not comfortable running it through a standard relay that is rated for 40 amps. So I took Tom Rowe's advice and ordered a Cole Hersee that's rated at 70 amps.
In other words, the answer to your question is that I'm bullet-proofing it.
Gary, have you worked out this part of your Dad's truck?
I have been trying to wade through all the info you have, as I'd like to follow your example for this particular project.
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