Good advice --- thanks.
I'll head to the pic n pull this weekend, and plan to wire in some relays for low-beam and high-beam.

Follow up questions:

1. Is it worth buying new relays or can I just scavenge some while I'm at the junkyard?

2. Do I use in-line fuses, or fuseable links, or ...?

 

Indeed, you can get 1 cubic inch relays off of another Aerostar. There should be like 3 of them under a plastic cover on the left inner fender toward the firewall. Of course, other cars will have similar relays, but I'm not sure where they would be.

Note that the Ford relays have a reverse-biased diode on the coil for suppressing back EMF, so you MUST watch which way you power it. If you apply current in the wrong direction, you will forward bias the diode, making it conduct the full power of the battery, and the diode will blow up in a millisecond, damaging the relay in the process. It will also make quite the firework. Check the wiring diagrams for this, or measure the wires going to the stock relays to see which coil pin gets + and which gets -.

Here is a picture of the wires I installed in my van:

https://picasaweb.google.com/lh/phot...mhFfQmQNkuk84Q

They are 10 gauge wires with inline fuse holders, good for 30 amps. The relays are on the side in front of the starter relay. I have a third one for a fog/driving light.

 

I would actually recommend purchasing a prefabricated relay harness that plugs right in. Here are the major benefits.

1. The relays have mounting tabs, and sealed connectors
2. No splicing or cutting required
3. Easy to install
4. Can be transferred not only to other Aerostars, but anything that uses the same bulb
5. In the even you are in the middle of nowhere and something goes wrong, you can unplug and bypass it.

 

Scavenge away! Most relays never die in regular service so used is a viable option. A few spares will give you a lifetime supply. You can look at a bunch of different cars ad find one that has a suitable fuse block that also has relays inside. If you are clever, you can then rewire the fuse block so your installation will look like a factory job and you can always add a new circuit should you have the need. The newer cars might be good donor candidates as they tend to have nice small under the hood fuse/relay blocks ripe for the picking.

For a neat job, look for some of that plastic wire loom cover. You can also harvest some of the correct colored wire to match the factory color code if you want. A hint here, sedans or pickups will have longer hoods and therefore longer wires than vans.

No difference electrically, the difference comes in as a matter of convenience. For example a fusible link is just a section of wire that acts as a fuse, easy to install but hard to tell if it blows. Plug in fuses are really convenient to service, but to install you need a fuse box. Inline fuses are kind of a compromise between the two.

Most cars do not fuse the headlamps because they don't want a fuse to blow on a dark and stormy night and have you in the ditch. One exception to this general rule is Mercedes, they fuse the headlights, but they have the left and the right fused independently.

Before you hit the junk yards, I would pencil out how and where you are going to run your new wires and how and where you are going to make splices.

If you can, it would be really nice not to have to cut factory wires but rather plug in a loom you make up with salvaged components. It gets a bit annoying working on a car that has a bunch of red wires running about even if you were the guy that ran the red wires

 

> Most cars do not fuse the headlamps because they don't want a fuse to blow on a dark and stormy
> night and have you in the ditch. One exception to this general rule is Mercedes, they fuse the
> headlights, but they have the left and the right fused independently.

Yet they have those thermal breakers in the headlight switch, which WILL blow at the worst moments, like when you're really depending on the lights.