Hello everyone.

I'm trying to help out my friend who is the proud owner of a 1993 Aerostar.

He has been having the headlight switch issues that I've read alot about on these forums (thank you to all who post their questions and answers here by the way). The thing is he replaced the switch and the plug module on the back of it and the problem just repeated (plug module melted etc.). All the other threads that I read about this problem seemed to end with the replacement of the switch and plug module.

When I got involved I took off the switch and started doing some tests with my multimeter. One thing that I noticed is that all the wires on the module have continuity between them except the red w/ yellow. The same wires have continuity to ground. In fact most of the wires on the back of the fuse panel have continuity between each other and also to ground.
He has not had any battery drain issues or really any issues other than the headlight switch, no running lights, no instrument panel lights and no radio light when the headlight switch is pulled out.

We disconnected the main harness from the firewall in the engine compartment and it didn't change anything. We've inspected every visible wire, connection, device etc.. There are no signs of arcing, melting or anything unusual in any visible location. The only other melting issue was at the actual sockets on the tail lights. The overload has caused some melting of the tail light housing where the socket attaches. All the wires to the tail lights however are beautiful as is the socket itself and the bulbs.

When I was reading the threads regarding the headlight switch problem there was mention of someone posting a thread that addressed the problem by installing some sort of relay in the headlight circuit that would take some of the load off of it. The people that mentioned it however did not link to the post or tell where to find it. If anyone has any info on it that might be very helpful here.

If anyone could please help us with this we would grateful. I'm hoping that someone who has had this problem or someone that has electrical know how could shed some light on this. Thank you.

 

Daniel Stern Lighting Consultancy and Supply



https://www.ford-trucks.com/article/...ay_System.html

 

look for HID lght. 35 WT xenon bulb is twice brighter then 65-10 wt halogen bulb. HID kits are really cheap now from $60 to 150

 

Watch out for cheap HID kits, as they tend to have very poor light distirbution, and they die early. If you do install a simple kit, you will lose high beam capability on the 2 light system of the Aerostar, and you have to re-wire the lights to prevent the HID low beams from shutting off when you try to flick on the highs. There are kits designed to emulate high/low beams in a 2 light system, but most of them are junk.

 

just noticed that both of these schematics the creators suggest going to the alternator 12+ charge lug.
that is a NO NO in my book. too much physical strain on the lug especially if one has upgraded the alternator and charge wire to a 4 ga or larger.

i always take my 12v loads on Fords to the starter relay +12v battery lug unless that is too full to keep tight, then i'll install an aux. lug point on the fireway with at least 4 ga wire.

alternator show have nothing added around it to restrict air flow even 1 wire.

 

what stock bulbs have 93-97 aeros? I had made of plastic lamps with soldered in bulbs and I swaped them with Hella H4 headlamps having much better light distribution (peole say that in 80-s H4 lamps were unlegal).

 

Most European spec'd (E4) headlights are not DOT approved for use on cars in the US for the technical reason that they do not have the the aiming nubs on the face of the lens. I think that rule has been lifted. But the E4 spec lights were legal for motorcycles for some reason, so a lot of them had "DOT" cast into the lens. But I think there is still some rule about the reflector and lens assembly has to be sealed.

There were some Japanese cars imported to the US that used flush mounted head lights that used H4 bulbs. I never looked at them up close, but they must have some way of sealing around the bulb base.

 

Thank you all for your replies.

Do I use the factory headlight switch for this?

Does anyone have any ideas about the ground situation I spoke of previously?

Since his battery is not draining and it doesn't seem to be causing any problems, would it be alright to just fix the headlight circuit issue?

Since the posted headlight circuit schematic was for a 78' Bronco how do I apply it to the aerostar circuit, what do I need to modify if anything?

Thanks again.

 

sounds like the headlight pull switch wiring loom socket or the headlight dimmer switch socket is melted and shorted or the wiring harness itself is melted with shorted wires inside
common for the socket on the end of the wiring harness to melt also. low grade copper alloy, too high current draw exceeding current ratings of switch and wires, poor cooling air flow to area

have to clear up the short problem or more switches will be burned out.

to add relays to the headlight output circuit, just wire the low beam relay output to the low beam lead on the headlights sockets and the HB relay output to the HB lead on the sockets

take the 12v pwr input of the relays directly to the pos + battery lead on the starter relay.

if you're not familiar with veh. wiring, have a shop do the headlight relay mode

 

Thank you 96_4wdr for your reply.

Do you have any idea where to look for the short?

I can't figure out how all the wires except the red/yellow (high beam switch wire) on the back of the switch have continuity to ground. I could understand
if it's one wire on one circuit but how across multiple circuits (as I said most of the wires on the fuse panel have continuity to ground as well). There are no other things shorting besides the headlight switch.

The wires on the back of the headlight switch (the tan/white, brown, and blue/red) are damaged from the problem but only right at the plug that goes to the switch. I followed them from there to the harness and they are healthy.

My friend got another plug that goes on the back of the headlight switch from a newer model and the wires on the back of it are the same colors but they are a much heavier gauge. Would it help if I re-run the wires in the affected circuits with a heavier gauge wire?

As far as the relays go, I'm assuming that you mean the 30A DPST relays mentioned in the above schematic. The first schematic shows relays with 3 terminals plus a ground. The second shows relays with 4 terminals plus a ground with one terminal from each relay going to one of the "old headlight wiring plugs". If you can clarify this just a bit I can handle the mod.

Thanks again.

 

remember, most of the hot 12v switched circuits in the Aero are usually switched near the batt. source so the rest of the circuit is near ground/chassis potential all the time thru the low resistance device being powered such as a headlight.

the problem may also be in the hi/lo beam multifunction stalk switch located on the steering wheel, these are a weak point also due to overcurrent overheating and use.

going to need an Aero electrical wiring diagram such as in the Ford Service cd/manual or a Chiltons with circuits and wiring colors to troubleshoot. too detailed to try and trace down via internet discussion.

30a SPDT auto general purpose relays are what i used for my headlight circuits mode. just adjust circuit for single headlight dual filament bulbs as in the Aero.

 

Those diagrams are somewhat misleading; the second diagram with the 5 leads on the relay actually has 2 separate leads going to the lights that can be just 1 lead going to both lights.

You can get these 30A 1 cubic inch SPDT relays from Radio Shack that are designed for this purpose. You would intercept the wires going to the head lights (separate low and high beams).

First, cut the wire going to say, the low beam. The end coming from the light switch will be used to energize the relay coil. The other end of the coil will be grounded. The end going to the lights will be connected to one of the relay contacts, and the other relay contact will be connected to the battery through a fuse. Repeat for the high beam.

About your headlight wiring problem, using heavier gauge wires can only help, even if you install relays. As to trying to find the short, you might have to use jumpers to trace out each circuit to each switch lead. Look for the wiring diagram for your model in the Ford CD, or Chilton's. Good luck.

 

What we did on my moms van after the plug melted was to use ordinary spade connectors and just do one wire at a time and plug it onto the corresponding spade. You can also buy new plugs through rock-auto.

As far as the relays,t he best way to go is to install a relay kit. If you buy the relays plus the wiring and the new headlight sockets, you will end up in the same price range as a kit.

The kit I used was this
Upgraded Headlight Harness for 94 to 04 Ford with 9007 Bulbs

This kit was extremely easy to install, no splicing, no soldering. You just connect it to the positive battery terminal on the starter relay, attach it to a good ground, and plug it into one of the headlight sockets, and plug the other ends into the headlights themselves. Quick and easy. The hardest part is routing it where it is nice and secure.

By installing the relays, you also make the factory lights brighter, assuming the lenses are not too badly fogged over.

 

Thank you to everyone. It is nice to have a place where people can get help to fix things themselves.

xlt4wd90: I'm in the process of tracing the short with that very method. Thank you for clarifying the schematics for the relays.

Bear River: The relay kit you linked to doesn't mention Aerostars at all. Are you sure it will work for my friend's 93' Aerostar or do I have to modify the kit?
Does the 93' have 9007 bulbs?

I'm almost done with this issue thanks to all of you. Your help and time is greatly appreciated. I can't say it enough.