78 351m woes
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New User
Joined: Feb 2007
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78 351m woes
hello all,my 351 m will rotate but will not start.It tries to start when i release the key in the run position.here is a list of things that has happened in the last 4 days.It quit running in the middle of the road,only to start back up about 10 min .later and run and start fine for a day.then all my gauges,radio, windshield wipers all quit working.the truck would start and run fine,only the headlight worked.got in the next day all was working fine ,i did nothing to fix the prob.the last 2 days i have replaced the switch and cylinder,the ignition mod,today. yesterday i replaced the pick up stat.the engine fired up as soon as i touched the key yesterday.today only rotates and tries to fire in the run position .i have fire from the coil when i turn on the switch spark,the when i release the key a spark,what am i missing???????
New User
Joined: Jan 2008
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Welcome to the Site & this Forum 
More than likely the ignition module on the fender is causing the problem.
You should have a "Motorcraft" unit for best operation.
The area under it should be clear to allow adequate cooling of.
Take yours in for testing.
Sometimes people have gone thru 4 of them to find one that works properly
More than likely the ignition module on the fender is causing the problem.
You should have a "Motorcraft" unit for best operation.
The area under it should be clear to allow adequate cooling of.
Take yours in for testing.
Sometimes people have gone thru 4 of them to find one that works properly
Ford Parts Specialist
Joined: Nov 2006
Posts: 88,826
Likes: 785
From: Simi Valley, CA
1977/79 12a199
There are two different modules used 1977/79. The number off the original will tell us which is correct. Or, there is a plastic tab (either RED or BLUE) where the wires plug to the module that can ID it.
Note: If your module has the RED plastic tab, be advised that this module has had quality issues from day one. Buying a used/rebuilt one is a waste of time, they're prolly defective too.
D7AZ-12A199-A RED Module
D9VZ-12A199-A BLUE Module
When the 1977 Fords/Mercs first came out, within weeks, there were 1000's of these cars & trucks parked on dealer service lots nationwide. The problem? Defective modules. And the replacments were on back order! When stock was finally released, half were worthless. Ford never did entirely solve the problem. Sometimes it took several modules to get the vehicle to run.
Note: If your module has the RED plastic tab, be advised that this module has had quality issues from day one. Buying a used/rebuilt one is a waste of time, they're prolly defective too.
D7AZ-12A199-A RED Module
D9VZ-12A199-A BLUE Module
When the 1977 Fords/Mercs first came out, within weeks, there were 1000's of these cars & trucks parked on dealer service lots nationwide. The problem? Defective modules. And the replacments were on back order! When stock was finally released, half were worthless. Ford never did entirely solve the problem. Sometimes it took several modules to get the vehicle to run.
Last edited by NumberDummy; Feb 13, 2007 at 03:17 AM.
