I just dropped in a new (new to me) 460. 78 with 70k original miles. Everything looked great when I had it apart. Now that its in the boat I have no spark. Hooked everything up the way it was on the previous motor but nothing. Im getting one strong spark when I first crank it over then major drop in voltage. Running a msd blast coil and a mallory dis. . Im puzzled. I dont do electrical real well and would love any and all advice so I can get this thing on the water before its too cold here in oregon. Thanks!
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Gonna need some info brother. First... Welcome to the boards....
Always good to have a newb to tease....
For starters. try this.
Using nothing but a 12v test light (TL), turn the key to the run position (not start), ground the clip of the TL and probe the (+) terminal of the coil. Do you have power?
No? check for a wiring problem at the dash or at the connections on the ignition circuit from the dash... Maritime wring this would be a purple wire, hillbilly wiring could be anything..LOL Don't forget about the ballast resistor if applicable.
Yes? Then test for power at the (-) terminal of the coil, it will be less power but should be able to light the light. Still no, then bump the starter while checking for a light (this is when that beer swilling neighbor really comes in handy...)...
Never a light? Something is shorted in the distributor circuit, could be the points, condenser, Hall effect sensor, magnetic pickup, whatever switches the coil, a bad ignition coil, Could also be the tachometer or related wring, maritime wiring for the tachometer is light grey.
To test the coil, remove the wires going to the (-) terminal and check again, there should be voltage present at the (-) terminal on the coil itself. (obviously with the key "on"...)
Light all the time? You have an open circuit going to the coil from the distributor or a bad (whatever switches the ignition coil)... Or a really bad ground to the block and or distributor body...
To check for a ground on the distributor body, clip the lead of the test light to the (+) lead of the battery and probe the distributor body... No light? Do you get one on the block?
Yes? Remove the hold down to the distributor and hit it with a file where the clamp touches the engine and the distributor and the areas of the block and the distributor where the hold down touches... There are some instances when you need to run a separate ground lead to the distributor body. I now do this out of habit...
No?, well there you go, problem found...
Other than that......
Have fun and good luck.
GT
