what do i need to convert to MAF

The computer, the harness that hooks to it and the meter.

MASS air conversion instructions from http://www.stangnet.com/tech/maf/massairconversion.html FREE
A9L (5 Speed) computer from junkyard $100-$150
A9P (Auto or in a pinch, 5 Speed) computer from junkyard $100-$150
70MM MAF from 94-95 Mustang GT - $40-$70
MASS Air wiring harness kit $30-$85

The whole thing is probably less than $300 using junkyard parts.

A9L computers are 5 speed only
A9P computers are automatic, but will work with a 5 speed.

The conversion harness seems to work well for most folks. It avoids the compatibility problems in using a harness from the junkyard. Simple and cheap, actually less work that swapping the wiring harness.
Conversion Harness kits & parts
http://www.mass-air.com/
http://fordfuelinjection.com/index.php?p=54

If the idea of moving & soldering wires scares you, here's a list of compatible Mass Air wiring harnesses.

Copied from bbunt302
Just for reference, here's a list of all the compatible years:

89 harness should work for 86-89 as long as you're using mass air.
90 harness will only work in a 90. (B/c of air bags and dual dash connectors)
91 through early 92 harnesses should be compatible (single dash connector, fuel pump relay under driver's seat)
Late 92 through 93 harnesses should be compatible (single dash connector, fuel pump relay under the hood)

Larger MAF to go with Mass Air conversion:
94-95 Mustang GT MAF - $40-$100. It is 70 MM instead of the stock 55 MM on regular stangs built prior to 94. It uses a slip on duct on the side that goes to the throttle body and a 4 bolt flange on the other. You need a flange adapter to fit the stock slip on air ducting that goes to the air box. Wiring plugs right in with no changes. *1 *2

*1.) Metal flange adapter http://www.kustomz.com/cat3.html Buy the TR70 for $44.95. Or spend some time on eBay looking for one that may fit.

*2.) MAF & sensor interchange
The 94-95 Mustang 5.0 MAF & sensor is also found on:
1995-94 Mustang 3.8L F2VF-12B579-A2A,
1994-92 Crown Victoria 4.6L F2VF-12B579-A2A,
1995-94 Mustang, Mustang Cobra 5.0L F2VF-12B579-A2A,
1994-92 Town Car 4.6L F2VF-12B579-A2A,
1994-92 Grand Marquis 4.6L F2VF-12B579-A2A,
Evidently the –A1A, -A2A, AA, etc. on the end of the part number is a minor variant that did not change the operating specs. You should be able to ignore it and have everything work good.

that 91 harness won't work on your 87 car. sell the harness on ebay, and pick up an 88/89 harness (88 california)...use the mass air meter and ecu from the 91

v8only said:

that 91 harness won't work on your 87 car. sell the harness on ebay, and pick up an 88/89 harness (88 california)...use the mass air meter and ecu from the 91

Click to expand...

Some input as to why the 91 harness doesn't work would be helpful. That will enable me to update the tech note I have.

computer harnesses are specific to the range of years, 87-89 swap, and 90+ swap.

Let me find more solid evidence later and I'll post it.

jrichker said:

Some input as to why the 91 harness doesn't work would be helpful. That will enable me to update the tech note I have.

Click to expand...

Because in 90 they started using air bags. I would get a A9P computer which is from an automatic fox and a harness from an 89 and your golden.

FordGuy88 said:

Because in 90 they started using air bags. I would get a A9P computer which is from an automatic fox and a harness from an 89 and your golden.

Click to expand...

Would you mind elaborating?

The ecu isn't wired into the air bag system... it should be completely separate...

but the air bag in a 90+ is wired into the harness unlike the ones below if im correct.

v8only said:

that 91 harness won't work on your 87 car. sell the harness on ebay, and pick up an 88/89 harness (88 california)...use the mass air meter and ecu from the 91

Click to expand...

you are 100% correct

v8only said:

that 91 harness won't work on your 87 car. sell the harness on ebay, and pick up an 88/89 harness (88 california)...use the mass air meter and ecu from the 91

Click to expand...

Or just cut the 4 wire MAF plug off the donor and make your own. Since I did not have the harness, I cut a MAF plug from a 4 cyl car and made my own 4 wire maf plug to the computer and soldered every joint and ran it through the rubber grommet that holds the ECU main harness to the ECM and used a old 60 pin connector to rob pins from for the 2 signal wires. I also bought some black wiring harness tubing from the auto parts store to make it look stock.