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Hoping for a little help/knowledge. 2 months 1 week ago #137470

  • 69Jetflte
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I have a 1973 Mercury 850 Thunderbolt, I have run all the tests and everything points to a bad trigger/pick up in the distributor. Only time I have spark is when you let off the key. Any help would be greatly appreciated, can not afford to just replace the switch box and trigger or I would!!

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Hoping for a little help/knowledge. 2 months 1 week ago #137477

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Could being out of time cause this?

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Hoping for a little help/knowledge. 2 months 1 week ago #137484

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Nope, the symptoms point to a bad trigger.

Here's a test you can do to confirm the rest of the ign system:

MERCURY BATTERY-POWERED CDI TEST FOR DISTRIBUTOR MODELS

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

This test assumes your coil is good (problems with CDI coils are rare).

DISCONNECT BATTERY

1. Turn off ignition;

2. Disconnect all 3 distributor wires on the Port side of the switchbox (and the “mercury switch” if present);

3. Remove the HV lead from the ign coil to the center of the dist. cap (remember it unplugs from the coil and unscrews from the cap);

4. Reconnect the HV lead to the COIL only;

5. Position the free end of the HV lead approx. 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 to each other.

RECONNECT BATTERY

7. Check that you have +12V at the red terminal (even with the ign off);

8. Turn on ignition and verify +12V at the white terminal (same side as the red terminal);

9. Ground the black terminal on the distributor side of the switchbox - this should cause a spark each time you touch ground.

If you get spark with the distributor bypassed, and it won't fire with the distributor connected, the trigger is bad and the entire distributor housing assy must be replaced.

If you get no spark using the test, the switchbox is probably bad. In that case, be sure to check for correct power on the switchbox, check all connections, and check the coil's resistance to make sure it's OK.


The CDI Electronics replacement trigger is probably the best, you'll probably find the best price on eBay. You can also search for used ign parts but they usually bid up $$$ and any old Merc distributor trigger is usually a ticking time bomb as to how long it'll continue to work.

HTH............ed

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Hoping for a little help/knowledge. 2 months 1 week ago #137492

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Thanks for the info, we ran that test and I have really good spark out of the coil. I kinda figured it was the trigger, was just hoping!! LoL I guess I am going to have to drop the money on a trigger!😒

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