Pickup: 1987 F-150 with 351W. I posted this here rather than the 87-9x subforum because the 351 was left carburated while the other 87 models were EFI.

Backstory: drove this truck through highschool/college, then parked it in the barn for about 6 years.

Bad news: rats built a *huge* nest in the engine bay, and chewed through some wires.

Good news: radiator still full of bright green fluid, carb/intake was covered up so nothing could get down in the engine.

The problem: 12v to both sides of the coil, but not getting any spark when cranking.

Replaced plugs/wires/cap/rotor/ignition module. You can see from the pics that the wire from the harness to the oil pressure sending unit is shot, but I wouldn't think that would cause a problem with *spark*.

New ignition module plugged into the wiring harness. Not sure what the 2nd pigtail is for. . .


Coil, and associated wiring.

 

When you say you've got 12v at both sides of the coil do you mean if you pull the wire from the Coil to the Cap you have spark?

 

No, sir. With the key in the start position, I have 12v on both the + and - coil connections, but no spark out of the coil.

 

So you've replace pretty much everything but the coil. Got 12v going into the coil but nothing coming out of the coil... I think I'd try a new coil. Not gonna hurt, if ya get a new one and throw it on and it still doesn't work it's easy enough to pull off and take back.

 

Naw, I replaced the coil also. . .just didn't get it added to the "things I replaced" list.

 

You got a test lamp with an alligator clamp?

Put the clamp on the Positive of the battery and the lamp point on the neg side of the coil. Have someone get in and crank the truck over, with the truck cranking the light should pulse.

 

Wait? Is that Pig tail with the red and white wires plugged in to anything?

That should be power coming from your ignition key.

 

No, and unless I'm optically challenged as a bat (have to be politically correct here ) I don't see anything *to* plug the red/white pigtail into.

But I'll go look closer. . .this OU/Texas game is making me sick to my stomach. Need a good excuse to go outside for awhile.

 

You know what? I'm an idiot. I looked at the old module, and sure enough the red/white pigtail was plugged int something. . .and the something was still plugged into the old module, with two wires, chewed in half, hanging out.

Doh!

 

Here's a wiring diagram that should help ya trace some wires. Other thing to check out while poking around is to make sure those wires coming from the Starter Solenoid are good. OH and that should lead back to your missing plug.

 

To Make the truck run just use a jumper wire from the battery + to the red wire on the IGN module. This is what powers the IGN module and it will not work if you dont give it power.
You really dont need to use the white wire in the 2 wire plug if you dont want to mess with it. It shoud be easy to follow the wires back from where the rat chewed into them. The red wire should have 12 volt with the key in ON and START.... the white wire will have power in START key position only.

Jim

 

Are you absolutely positive about that? That doesn't sound right to me (but I don't know
the specifics for certain).

 

Yes, it's right.
The white wire tells the DSII box to retard the spark in Start and relieve load on the starter motor.

 

This was based on actual measurements I had on my truck. I checked this during the switch to a DS2 system.

 

Originally Posted by ctubutis
Are you absolutely positive about that? That doesn't sound right to me (but I don't know
the specifics for certain).

This is a complicated issue. Both of you are 100% correct.


This is because it depends on if you have a aftermarket or replacement module or the original factory module.

Factory Modules are color coded:
Red/Lt. Blue: Start.
White/Lt. Blue: Run.

Some aftermarket and some motorcraft replacement modules have these wire colors inverted at the connector.

Red for white, and White for Red.

Evidence of this can be seen in this picture.



This is why the colors invert at the connector on replacement modules. The truck harness wiring remained the same and matches the factory module, while the replacement module harness swapped colors. Why also some aftermarket diagrams are contrary (like the one posted above) to the factory diagrams.


This is why, both of you are correct. Also makes it confusing as heck.

Don't uncross the wires (if they cross like in the pic) otherwise it will be wired wrong. Also if you have an original module, the wire colors will match all the way from the truck harness to the module. (Don't make them Cross).

Hope this helps.