74' merc 150 no fire. help?

it looks like i got no spark. i have checked for power at the switch box and it seems to be ok.

i see three parts in this ignition system. are there any tests i can do to narrow it down?

thanks john

-W

i unhooked the coil wire and it was extreemly croaded at the coil end. so i tryed cleaning it and the in side of the coil too.

i thought for sure i found the problem so i tryed to start it after cleaning. still nothing.

i am going to try your test this weekend. i am guessing this coil is junk. any chance you got ohm specs for it?

thanks JOHN

The coil on those is the LAST item to suspect. The switchbox or trigger is most likely. I havn't see a bad coil on one of those in over 5 years... and that's saying something.

-W (is yours the big orange coil or the smaller one that mounts to the block?)

also i did check it last night and got what seemed to be a vary low reading on my dvom.

thanks john

-W

JOHN

-W (that orange coil was WAY overkill)

This test is for the 332-2986 switchbox used from 1967-1978 on all the inlines.

This test assumes your coil is good (most all are).

DISCONNECT BATTERY

1. Turn off ignion 2. Disconnect all 3 wires on the distributor side of the switchbox. 3. Remove the HV lead from the coil to the center cap (remember it unscrews from cap) 4. Reconnect that HV center lead to the COIL side only. 5. Position that HV lead about about 3/8" from ground (block, shrouds etc) and find a way to hold it there. 6. Jumper the brown and white terminals on the dist. side of the switchbox together.

RECONNECT BATTERRY

7. Check that you have +12 V at red terminal. 8. Turn on ignition and verify +12V at white terminal (on red terminal side) 9. Touch the black terminal to ground - unit should cause spark each time you touch ground.

If this passes and it still won't fire at all, suspect the trigger (distributor).

To test replacement trigger if/when switchbox passes test: Remove jumper wire and hook up the 3 wires from the new distributor to the switchbox, turn on key and manually spin the distributor, spark should jump from coil wire just like in the switchbox test.

POST BACK HERE IF YOU NEED A USED SWITCHBOX OR DISTRIBUTOR.

-Wayne

i will test it and report back.

john