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Discussion Starter #1
How I solved My low voltage problem. Plus upgrading power distribution.
I will be posting a complete walk through with lot of pictures over the weekend.

Anyway, here's the deal.
14.1 V at battery, warm engine, idle. Nothing on. Voltage measured at fuse box, 11.6-12.4
Measured at lighter socket 11.9. if window is rolled down, system voltage drops below 10.
Battery stays above 13.8 and recovers to 14.
wipers slooow, windows slooow, door locks slooow, fuel pump sounds sick.
It's been that way since I bought the truck back in 2002.
I did the 3g upgrade 2 years ago. electric fans and headlight relays last year.
Now that I have opened my own shop this year, I have more time and a place to work on it.
I solved one of the most common complaints in these old trucks. More to come.
 

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How I solved My low voltage problem. Plus upgrading power distribution.
I will be posting a complete walk through with lot of pictures over the weekend.

Anyway, here's the deal.
14.1 V at battery, warm engine, idle. Nothing on. Voltage measured at fuse box, 11.6-12.4
Measured at lighter socket 11.9. if window is rolled down, system voltage drops below 10.
Battery stays above 13.8 and recovers to 14.
wipers slooow, windows slooow, door locks slooow, fuel pump sounds sick.
It's been that way since I bought the truck back in 2002.
I did the 3g upgrade 2 years ago. electric fans and headlight relays last year.
Now that I have opened my own shop this year, I have more time and a place to work on it.
I solved one of the most common complaints in these old trucks. More to come.
And your Noobie Technical question is? or is this just an ad for your shop? The three most common problems here seem to be are "my truck shifts hard", "my tailgate window doesn't work", and my ground wires are loose/corroded.
So, keep us in suspense, or just replace the block and frame ground.
 

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Discussion Starter #4
The fact that these trucks did not have the best electrical systems leads me to believe Ford didn't have good electrical engineers at the time.
But all cars in the 80's suffered the same.
A Bronco was my first ride and will always be my ride.
17 years working for GM on odb2 era cars, has shown me better electrical systems. and all makes follow the same methods now.

A Bronco or f series truck gets power to everything through 3 12ga and 2 16ga wires attached to the starter solenoid with fusible links. Those wires run around the radiator support and down the left fender where they feed the eec and fuel pump relays and then into the cab to the fuse block and ignition switch. On the electrical diagrem all these wires are called circuit 37.
This barely provides enough amperage to power basic systems much less added on accessory's. And when time takes it's toll on wires and connectors, this can reduce current flow.

What's needed is a better pathway.
 

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Discussion Starter #5
I re-engineered the circuit. I first disconnected the battery, It was time for a replacement anyway. I then removed the fusible links at the solenoid. Moving over to the left fender I identified the wires in the harness and started my modifications.
I ran a 6 gauge cable from the battery to the new junction box. This will provide more current than the original set up.
Wiring this up was a day long project. Probly 10 hours of cutting soldering and starring at pages and pages of wiring diagrams for two different trucks.

The results are staggering. everything works better. More than 13 volts measured at fuse box and lighter socket. Roll windows down and voltage holds. Lights are brighter, radio is louder with more bass.


The following pictures are of the instillation of a battery junction box from a late model f150 2009 ish I believe.
 

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Interested in seeing the rest. I agree though - I just got done rewiring my entire truck and it's a real eye opener seeing what is underneath the wire loom. Probably worked fine brand new but not at all surprising that issues develop over the years. Of course they also had to work against cost savings and ease of assembly, so I think that's where a lot of compromises were made.
 

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Discussion Starter #7
Unless your experienced in electrical systems and repair, understand schematics and creative. Don't try it. It involves a lot of identifying and cutting wires, plus a lot of planning and having all your materials on hand.
I sourced the battery junction box from the pick n pull. I knew I wanted a ford box and that model fit well. It has way more fuse and relay slots than you'll ever need but if you need them, you've got'em.
I used the fuse and relays as marked. Such as, eec relay, fuel pump relay, a/c relay. as well as headlamp and fans. all those circuits are in the box so I found the same circuits in the truck and connected them. It is much more complicated than that though.
A smaller box thats less complex might be easier. A jeep wrangler or cherokee from the 90's would be good.

The main point is to get a better power circuit to all the relays and fuses. A under hood fuse box is just better than all those fusible links. look under the hood of anything built after 1996.
 

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this is great, bummer its so difficult to achieve easily. I try and avoid electrical work like the plague. a quality write up with detailed instructions and pictures i feel is the key to allowing those who aren't so good at this make the improvements.
 

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Unless your experienced in electrical systems and repair, understand schematics and creative. Don't try it. It involves a lot of identifying and cutting wires, plus a lot of planning and having all your materials on hand.
I sourced the battery junction box from the pick n pull. I knew I wanted a ford box and that model fit well. It has way more fuse and relay slots than you'll ever need but if you need them, you've got'em.
I used the fuse and relays as marked. Such as, eec relay, fuel pump relay, a/c relay. as well as headlamp and fans. all those circuits are in the box so I found the same circuits in the truck and connected them. It is much more complicated than that though.
A smaller box thats less complex might be easier. A jeep wrangler or cherokee from the 90's would be good.

The main point is to get a better power circuit to all the relays and fuses. A under hood fuse box is just better than all those fusible links. look under the hood of anything built after 1996.
Damn, super great advice!
 

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Discussion Starter #10
I have a schematic I'm working on that shows what's needed to connect an 87-89 Bronco wiring to that f150 junction box. So anyone who can understand it can replicate what I've done. It'll be basically schematics for both trucks showing the connections, and a parts list.
 

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Discussion Starter #11
I'm still working on instructions to do this mod. Trying to keep it in layman's terms.
Basically it's schematics of a 87-91 bronco and 07-2011 f150
Highlighting f150 fuse box hookups to bronco circuits.
Although, for just a simple upgrade without a donor fusebox. You can replace the circuit 37 wires with a 6 gauge cable. Stop the cable at a terminal block and add inline fuses to factory relays and fuse box. The point is that the wires from the starter relay can't carry the current needed.
 

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Anticipating more.......

this would be a great modification for not only our 1981 Bronco, but also our 1969 Falcon Futura wagon.

Thanks for the idea and the input!
 

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Where do you think all that voltage loss came from? The wire, fusible links, connections, grounds? Interested...
the horrible 1g and 2g alternator and charge cable. The unreliable pre 92 relays.

A write up would be very much appreciated as we can all find 07+ f150s in the salvage yard and future readers years along can also.
 

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Unless your experienced in electrical systems and repair, understand schematics and creative. Don't try it. It involves a lot of identifying and cutting wires, plus a lot of planning and having all your materials on hand.
I sourced the battery junction box from the pick n pull. I knew I wanted a ford box and that model fit well. It has way more fuse and relay slots than you'll ever need but if you need them, you've got'em.
I used the fuse and relays as marked. Such as, eec relay, fuel pump relay, a/c relay. as well as headlamp and fans. all those circuits are in the box so I found the same circuits in the truck and connected them. It is much more complicated than that though.
A smaller box thats less complex might be easier. A jeep wrangler or cherokee from the 90's would be good.

The main point is to get a better power circuit to all the relays and fuses. A under hood fuse box is just better than all those fusible links. look under the hood of anything built after 1996.
A lot of people get scared of electrical work. 90% of it is PREP. Get FACTORY electrical diagrams of what you are modifying and factory diagrams of what you are trying to retrofit BEFORE touching a pair of cutters. Looking at a huge loom of wires, especially in a modern car is intimidating. Realizing that a HUGE portion of modern vehicles wiring is related to DATA and not power is one part of the battle. Isolate each circuit , figure out how that circuit connects / reacts to other circuits and go after it one by one.

I'm not a rocket scientist, but if I can take a complete wiring harness from a LS powered vehicle and adapt it to a 80's GM vehicle with basic tools and supplies (and the correct factory wiring diagrams) anyone can do it if you have patience and know how to strip / solder / measure voltages and resistance etc.

For something like the Bronco, and just updating and making circuits more efficient, I would think a universal type modern fuse box would work fine.

That's just lowly opinion.
 
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