I have a farm beater 1986 Ranger with a 2.9 4x4 manual.
It has been having intermittant issues that lead me to believe the computer is shot.
When I bought the truck, the previous owner handed me a box of parts saying "you might need these some day"
Included is a computer from a 1988 (also manual according to the junkyard paint)
I realize there might be small differences, but if I try a swap, will it work?
What's the risk?
Thanks for your conjecture.

If it is not the right computer the truck simply wont run so no harm

for it to work properly it will have to be a 2.9 4x4 manual computer

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Easy way to tell match the numbers up if thee sticker are present

Here are a list of possible computers for a 86 the ID numbers and letters are what u match up below this are the ones for the 88

1986
Ignition Cont, 4-122 (2.0L)
Ignition Cont, 4-140 (2.3L)
Elec Cont Unit (ECU), 4-140 (2.3L), MT, Calif
Elec Cont Unit (ECU), 4-140 (2.3L), MT, Fed
Elec Cont Unit (ECU), 6-179 (2.9L), Calif, AT
Elec Cont Unit (ECU), 6-179 (2.9L), Calif, MT
Elec Cont Unit (ECU), 6-179 (2.9L), Fed, AT, 4x2, cab and chassis
Elec Cont Unit (ECU), 6-179 (2.9L), Fed, AT, 4x4
Elec Cont Unit (ECU), 6-179 (2.9L), Fed, MT, pickup
Elec Cont Unit (ECU), 4-140 (2.3L), AT
Elec Cont Unit (ECU), 6-179 (2.9L), Fed, AT, 4x2, pickup
Elec Cont Unit (ECU), 6-179 (2.9L), Fed, MT, cab and chassis
Elec Cont Unit (ECU), 4-122 (2.0L)
Ignition Cont, 6-179 (2.9L)

1988
Elec Cont Unit (ECU), 4-140 (2.3L), AT
Ignition Cont
Elec Cont Unit (ECU), 6-179 (2.9L), Calif, MT, 4x2
Elec Cont Unit (ECU), 6-179 (2.9L), Fed, AT, 4x2, ID E8TF-M1A
Elec Cont Unit (ECU), 6-179 (2.9L), Fed, AT, 4x2, ID E8TF-M2A
Elec Cont Unit (ECU), 6-179 (2.9L), Fed, AT, 4x2, ID E8TF-MA
Elec Cont Unit (ECU), 6-179 (2.9L), Fed, MT
Elec Cont Unit (ECU), 6-179 (2.9L), Calif, MT, 4x4
Elec Cont Unit (ECU), 6-179 (2.9L), Fed, AT, 4x2, ID E8TF-S1A
Elec Cont Unit (ECU), 6-179 (2.9L), Fed, AT, 4x2, ID E8TF-S1C
Elec Cont Unit (ECU), 6-179 (2.9L), Fed, AT, 4x2, ID E8TF-S2A
Elec Cont Unit (ECU), 6-179 (2.9L), Fed, AT, 4x2, ID E8TF-S2C
Elec Cont Unit (ECU), 6-179 (2.9L), Fed, AT, 4x2, ID E8TF-SA
Elec Cont Unit (ECU), 6-179 (2.9L), Fed, AT, 4x2, ID E8TF-SC
Elec Cont Unit (ECU), 6-179 (2.9L), Calif, AT
Elec Cont Unit (ECU), 6-179 (2.9L), Fed, AT, 4x4
Elec Cont Unit (ECU), 4-140 (2.3L), MT, Super Cab
Elec Cont Unit (ECU), 4-140 (2.3L), MT, Reg Cab
Elec Cont Unit (ECU), 4-122 (2.0L), ID E87F-9L513-AA
Elec Cont Unit (ECU), 4-122 (2.0L), ID E87F-9L513-BA

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Thanks STL,
I swaped out the computer today (put the 88 Bronco computer in my 86 Ranger 2.9)
Started right up So far so good.
Only difference I noticed was the idle seemed a bit high. Not a huge amount, just enough that i kept waiting for it to drop back down but it never did.
Now I'll just wait & see if the intermittant problem shows up or is gone.