my 77 f150 ranger will simply shut down while rollin down the road. seems like it loses all spark. any ideas what the deal might be. cant find any broken or frayed wiring.

 

It should be a Duraspark ignition, so its a possibility the control module is getting hot. Lot of times you can see where they get so hot the epoxy starts melting on the back. Coil getting hot is another possibility, but the list really goes on and on. This just the ignition portion.

 

My vote too, Control Module.

 

Does it start right back up, or does it take some coaxing?

 

My uncle used to have the same problem so he always poured some water on the control module to cool it off.

 

the same thing is happening to my 77 f-250. i replaced the ign. con. module, then the coil, still dies. then checked the wiring, no shorts..then changed the key switch, still dies. it seems that the coil is shorting, but i can't isolate the cause. i tested continuity in the harness from coil to module and down to dist. wires were fine. i cut out the sockets and hard wired the distributor and control module, still dies... when runnig, i can swap coils, and modules with the same end result, she just dies after about 30 mins. of running..anyone got a REAL clue as to what the heck is going on? it is actually getting worse, it takes over an hour to recover, but then will runn like nuthin' ever happened.. til it dies again..i have good grounds at the batt. and engine to cab, she'll crank for hours, but no spark.

 

In your case I would suspect the pickup coil in the distributor. You should read 400-800 ohms between orange and purple and at least 70K from either one to black. Attacheded is the full test procedure for the DSII if it loads, having difficulty this morning.

 

wow. ok. that might help.

 

although i don't remember seeing a ballast resistor in the primary circut..

 

Use to have the same problem with my 77. Traced it to the connection on the control module. Had to polish the contacts inside the plug with some very fine emmory cloth and do the same to the module. Then coated it heavily with the type of grease they make for electrical connections under the hood. Solved it for me.

 

If you still have the horse shoe style clip on the coil it could be that the wire on the + side of the coil is loose, I've had that happen before.

 

It's not a resistor as such, but a resistor wire. Just a pink wire with a extra covering on part of it. You wouldn't think it, but it is actually 60 long and measures 1.4 ohms. When in use it will feel warm to the touch in comparison to the other wires.

 

yes, i know this wire, it shares the terminal at the key switch with the red/green wire to the coil. it does get warm. so does this wire need to be replaced, i have suspected it all along, does it trip like a ballast resistor?

 

If you mean go open like a circuit breaker or thermal breaker, no. It's either good or bad, not intermittent. I have never seen one go bad.

 

Have you checked the pickup module in the distributor yet? You're not looking at significant root causes. 99% of the time, when the ignition simply cuts off, the issue is the ignition module, or the pickup module. They get too hot, and they fail. The ignition module has a little harder time surviving because the case design is not heat sunk properly. The pickup module just gets old after 30 years.

You need to perform the resistance check per gfw1985's outline. This test will eliminate any catastrophic failues, like an open or short. Note, however, that the Hall effect sensor in the module is an active circuit element, so a resistance check won't tell you anything about it's functionality - so it's possible that it will ohm out fine, but still not work properly. Especially if the failure is heat-related, which is the case 99% of the time. In other words, if it passes the resistance check, it still doesn't eliminate the pickup module. However, I absolutely hate recommending to replace something unless there is hard evidence (that you can measure with numbers) that it has failed - unfortunately it's not possible to get that confidence with the pickup module, using standard tools.

Why do you suspect the ballast resistor? It's very easy to focus on items that look mysterious, or are easy to access under the hood - but proper diagnostic procedures and the process of elimination under the guidance of others are the key to solving any problem. The ballast resistor is just that - it's a specially doped wire that builds up resistance over its length. It's simply a kludgy way to reduce the coil primary current, which takes some of the load off the power transistor in the ignition module (or the points, before breakerless ignition). One advantage to making it a wire (as opposed to a single element, like in some Chrysler applications) is because it spreads the heat out over a long length, instead of focusing it on one single piece. The only way it can really go bad is if someone fuses it out by trying to wire loads off the coil positive terminal. The term "ballast" refers to many different applications - when used here, it simply acts as a fixed resistor.