jkelley22

hobolabo

Well you didnt say what year so I'll tell you about my same issue on my 78' F350 with a 351M, it was the grey brain box on the drivers inner fender. The only thing it controls is the distributor, i carry a spare (just in case) since they're kind of inexpensive and a nut driver just in case it craps out again. When they do ...at least mine, its all of a sudden kind of a thing, within 10 minutes i can be back on the roll again.
The spare has been in truck 18 or so years now, cheap insurance!
Good luck and reply when you find out what the problem was, could be a bare ignition wire grounding out also, had one of those too... different vehicle though.
Don't forget to give some details on your ? vehicle.

hobolabo

Summer 2000, building a new replacement bed


Jan, 2017 B4 a cab off restoration

jkelley22

So no baseball tourneys this weekend....I was able to work on the old truck...I have power going to the Dizzy through TFI Module & within inside the Distributor , I used the test light to check everything inside the dizzy I even touched the very top of the Distributor shaft without the Rotor Bugg on it and it lit up the test light BRIGHT ...I have power at the coil...So I put the rotor on and attached my led test light to the tab of the rotor and no Light , I even turned it over and No light ...So is the Rotor Bugg bad ?... Now my Starter relay is hanging up and when I turn the key on it turns the engine over even after turning ignition off...I have to go out there and hit the Starter relay with screwdriver to stop...I swear if its not one this its another ....My patients starting to run thin ...But I shall not be defeated...Feel free to chime in if you have any Ideas ...Thanks in Advance

88xlt

That doesn't seem right, atleast to my way of thinking. Are you using a test light which does not contain a battery? Or are you using a continuity tester which contains a battery?

jkelley22

88xlt

Where did you have the other end of the test light hooked to? If you had it hooked to a 12 volt source or the coil, touching the top of the distributor shaft would just ground the test light and make it light. I'm thinking touching the test light to anywhere on the metal part of the engine in that case would light the test light?

jkelley22

88xlt

No, not really. Any place that GROUNDS with the part of the live circuit you are testing for will work. It may be better to hook it somewhere on the engine.

Anyway, the reason I questioned the test light lighting when you touched the top of the distributor shaft. I'm thinking that shaft should be insulated(isolated) from the power source, as it hooks direct to the camshaft gear and would actually be a ground source.(not actually used to ground for the distributors working) I can't figure out why the test light would light going ground to ground. BUT MAYBE it is my thinking that is grounded, I don't know.

265258

I have a 1986 F-150 and I had a similar issue. The difference is, when I had the issue I was gutting that entire ignition system you are working on and swapping to a vacuum advance distributor. The trouble I had was simple, when I swapped to the vacuum advance distributor, I was trying to use the coil from the HEI ignition, once I had the right coil my problem was solved. I was getting power to the coil, but no fire. I had the same exact issue you are talking about with my test light, I couldn't figure out why the HEI coil would light the test light on both Ground and Positive, I never did completely figure out why the coil would appear to have two positives, but it was operating normal, lol. I'm guessing you are having an issue with the starter circuit. There is a Blue/Red wire that runs from your ignition switch to the starter solenoid, it also runs to your HEI. The HEI uses the signal to adjust timing while the engine cranks until the motor starts, after the truck starts it is redundant. I can't remember exactly whether that wire runs from the ignition switch to the Brainbox, or directly to the distributor, but I'm thinking it is the culprit and the reason you are not getting spark. Even after I switched to the Vacuum Advance Dizzy with the older Electronic Ignition unit from a 1980, it still uses that circuit. On my truck, that Blue/Red runs to my Electronic ignition unit mounted on my fender well, which probably retards the timing temporarily until the truck fires, If I unhook that wire, my truck will not start, even if the coil is getting power, I would start there with that pesky Blue/Red wire. You mentioned replacing a lot of parts all at once, maybe one of the parts you replaced was for another year truck? When I was studying all this crap to make the swap, I noticed in the wiring diagrams there are a lot of changes from year to year with the wiring color coding and components. Make sure you have the right parts.