I don't know exactly what the cutoff year is . . .
To recap:
Aerostars could be ordered with a factory towing wiring setup. If yours has factory towing wiring, there will be two roundish connectors underneath the back, just to the right of center, about 3" behind the bumper, and they are plugged into dummy terminators, to keep them clean and up out of the way.
You will also have a Trailer Tow Relay Module (TTRM), located on shorty Aeros behind the left wheelwheel, behind the jack. It's a roughly triangular aluminum box. If you just have a black plastic insulation "pillow", you don't have the TTRM. I do not know where the TTRM is located on extended-length Aeros.
The idea is to be able to wire your trailer (using a Ford adapter harness,
purchased separately, on the trailer) so that when you plug in this Ford adapter into the two towing plugs underneath, the TTRM is enabled, and the RightTurn/LeftTurn/Brake/Running/Backup lamps on the trailer are powered by relays in the TTRM, and not via the normal circuits for the van.
It's worth repeating: even if you have the optional factory-installed towing wiring setup and TTRM, it's the trailer adapter harness that enables the system. The towing connectors are more or less completely DEAD unless you plug in the Ford trailer adapter harness to the towing connectors.
I visited my Ford dealer yesterday and was told that Ford no longer supplies the trailer adapter harness for Aeros prior to '93 (which is why the subject of this post is worded the way it is).
Today, armed with wire cutters, I visited three junkyards and got luky: I found ONE Aero (a '90) with the Ford trailer adapter harness still installed (that owner used the trailer adapter harness to build a further adapter to his trailer wiring, probably so that he could use his trailer on more than one vehicle. Smart.), so I have a sample. Not too surprisingly, it's wiring matches the schmatic on the AllData CD.
On the theory that I, or one of you reading this, might want to built this trailer adapter harness yourself (rather than taking the easy way out, chopping off the undercar connectors and using the wiring pinout I posted earlier to build your trailer adapter that way), I walked up and down the rows, looking for a source for the two connectors, and I found them. The list that follows is for the connectors you need
to plug into the optional factory-installed towing harness under the Aero.
Two-pin connector:
1)
Good: The charge air sensor (about halfway back on the left side of the intake manifold (right side as you view it) on the top) from pretty much any 3.0l in any Aero is the right connector. I looked at about a dozen, and they all look correct. Note that the easier-to-get -at coolant sensor on the 3.0l (right up front, above the water pump) has the mating "square edge" on the wrong side, so forget using that one. The wiring is of a rather light gauge, but that's OK, because if you recall, the wiring in that connector does real light work:
Black: ground it to enable the TTRM
Black w/pink: backup lights
Cut it off the donor harness.
2)
Better: '87-88 Aero: There is a good connector under the air filter. It is not on two '88s I looked at, nor on one '86. I have no idea what it feeds. Follow the A/C harness from the compressor back up to the body, past the first connector, and where it meets the fat harness just in back of the air filter housing (and below, to the left of the fan) is a short (2") harness with the correct connector. It has heavier wire than the above. Cut it off the body harness.
3)
Best: Any '87-91 Taurus w/AT. I don't know what it's for -- possibly the radiator fans -- but on every Taurus within those years that I looked at, they all have a white ceramic resistor block bolted atop the automatic transmission, and the body harness connector to which it connects is perfect. Heavier gauge wire than the one above.
Four-pin connector:
1)
Good: '86 Ranger w/2.3l 4 cylinder, FI, and manual trans. The oxygen sensor harness on the FI rigs is for the heated EGO, which seems to have three wires. The harness has four wires, though; where the fourth wire goes I don't know, but if you follow the oxy sensor harness from the sensor up to the body, where that lower harness connects on the right fenderwell is the perfect connector. Cut it off the body harness.
2)
Better: '84-86 T-Bird or Cougar. On the left fenderwell, to the rear of the coolant recovery tank (which is bolted above a rack of vacuum solenoids), adjacent to the A/C compressor, is a bunch of harness-to-harness connectors, one of which is the correct one. Watch out for the gender, because I can't describe to you which one to take, because they're both body harnesses -- of the few I harvested, the correct one was the "front half". You want the "larger" half. On every one I pulled, the connector has all four wires wired/pinned, but the two black (brown?) wires were stubs and only 3" long. Good for us!
3)
Better (maybe): '87 T-Bird. This may be a one year only thing, because '89 is different, and I didn't see any '88s to compare. Find the wiper motor (driver's end of cowl, top of firewall, in engine compartment) and there's our connector, along with two or three other ones. Some of the wires are a bit heavier than the ones above. Watch for the gender. You want the "larger" half.
Armed with one two-wire and one four-wire connector (and the pinout below) you can make your own Ford trailer adapter harness. Use the wire color on the undercar harness and the list below for function:
Code:
Four-wire round connector:
Left turn: LG/O (Light Green w/Orange stripe)
Right turn: O/LB (Orange w/light blue stripe)
Running: BR (Brown)
Ground to van chassis: Bk (Black)
Code:
Two-wire round connector:
Backup light: Bk/Pk (Black w/pink stripe, Smaller wire)
TTRM enable: Bk (Black, larger wire)
Connect the two-wire's black to the four-wire's black using the pigtails on the connectors you harvested from the junkyard (those colors will vary, of course). That connection will enable the TTRM, and you also use it for the ground on the trailer.
The backup light is optional, of course, and you don't have to connect it to anything. Most especially,
don't connect it to the TTRM enable (which is what you would guess, if you were guessing).
I harvested enough connectors today to build a couple more harnesses, should someone be interested in buying one pre-soldered and ready to connect to your trailer. Optionally, give me a pinout of your trailer's existing connector, and I can solder on a mating connector on this end, so it would be "plug and play" for real.
But the data above should allow "anybody" to build it themselves. As usual, it's not too difficult -- once you know how
Regards,
Al S.