TOPIC: No spark on 69 merc1000

Hello hello, I have a 69 merc1000ss that I am trying to restore. My switch box and coil have passed the spark test while on the work bench! Install switch box and coil and no spark. 12V on the red with the key off, 8V on the white with the key on, I was expecting 12V on the white with the key on like the manual says. Am I getting resistance somewhere in the wiring harness? The internal wiring harness passes continuity test, I was unable to do a continuity test on the external harness at this time, the ignition wiring in the control box does not give me much confidence though! Is the ignition switch able to be replaced if necessary? Any suggestions for this type of problem? I don't mind getting a new harness if that's what it takes but I hate to buy parts without diagnosing as best I can!! Thank you thank you!

Yeah, I don't even think the switchbox will spark if the voltage is that low.

You might try running a jumper directly from the (+) terminal of the battery to the white terminal on the Stbd side of the switchbox.

Then spin the motor over and see if you get spark.

If you do, you have a high-resistance connection somewhere. It could be the ign switch, external wiring harness, the pin connections themselves, or you internal wiring.

You can isolate the low-voltage problem by unplugging the external harness and measuring voltage on terminal "F" of the harness with the ign key in the "ON" position.

If you don't get 12V-nominal there, the problem is external to the engine. If you do, disconnect the white wire from the switchbox, reconnect the external harness, turn ign "ON" and measure voltage on white wire to ground. It should be battery voltage. If not, there's an issue with the pins in the harness or the wire itself.

I've attached a wiring diagram and here's a general test procedure for Merc CDI igns such as you 1000's:


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.

Since you've already bench-tested your switchbox and coil, the only issues you'd have with them once reinstalled would be wiring and inadequate grounding. Make sure the ground straps for the lower cowl are installed, and also any braided ground straps between the front cowl support and the engine itself. It wouldn't hurt to make a couple of ground straps and install if you don't have any ground straps on the upper cowl/supports.

If you resolve the 8V-to-white-terminal problem and still no spark with everything (including distributor) hooked-up, I'd try the CDI test procedure thru step 9 to diagnose the distributor.

Obviously you've got to get to the point where you can get spark with the distributor bypassed, before you can be sure the distributor is causing the problem.

Unfortunately if you find the distributor is bad, the replacement is quite expensive. As I recall, the 1000 distributor may be a bit shorter than later models, but it's the rotor shaft that's different. Far as I can remember, the distributor housing (the main body of the dist) is the same as later models and you can get a CDI electronics replacement.

HTH & let us know what you find......ed

Thank you very much for the thorough response! I'm going to test the wiring tomorrow for correct voltage! I appreciate it! I'll let you guys know what the outcome is soon as I can! Thanks

Okay, did some voltage tests this morning! Unhook external harness from internal harness, connect battery, turn on key, got 11 volts on the F terminal, battery reads 12.6volts, so I am losing 1.5 volts in my external harness to start. Unhook battery and white and red wires on switch box, connect external harness to internal harness, reconnect battery, turn key on, 8.5 volts on the white wire, so it's losing 2.5 more volts by the time the voltage gets to the switch box. Disconnect battery, disconnect external harness, connect wire directly to F terminal of internal harness, 12.6 volts directly from the battery on the internal harness when the voltage doesn't have to pass through the connection between the external harness and the internal harness. Is the external harness able to be repaired? I cleaned the inside of the 6 pins(female) on the external harness with an old copper bore brush, I may try that again more thoroughly. What does all this mean though? I understand losing 1.5 volts on the external harness, because of broken insulation or corrosion, but what would be causing resistance when the voltage tries to pass through the external harness to the internal harness?! Hope this makes decent enough sense! Thank you all I appreciate your help very much!

First - I am by no means an expert...that said, I just remember people always telling me that any corrosion/contaminated connections make it hard for 12 volts to pass...I just think of the first example I was shown with a bulb in trailer wiring. A light was not working and the guy removed it, then quickly scraped it on the concrete pavement and put it back and it worked. Same with the plug connections at the vehicle/tongue connection. I was amazed how such little "green" or any non-clean surface stopped the 12 volts from getting through. Even just battery terminals on the old clamps on cars. A car would not start (nothing)...as he had the hood open looking at all of the green fuzz on the connection, a guy poured his Coke on it and said "now try it" that acidic Coke really foamed for a few second...he hit the starter and away it went. I guy gave me some Copper Paste called "Copper Shield" to put on my tractor battery terminals after cleaning...no problems for over 20 years. It is thick and believe it was expensive stuff...but clean connections and no air to allow corrosion helped me. Is there a way you could do an Ohm check reading on a new harness (before buying) and compare it to yours? Also, is the connection snug male to female?...does the male end have a split where you could expand it slightly to ensure and snug fit? (as I have now confirmed - I am no expert...just trying to help). Good luck!

If you have an accurate meter, you can measure the resistance of the white wire, from the "F" pin on the plug to the end of the wire. It should be a dead short (i.e. as close to "zero" ohms as possible). If not, you have a high-resistance connection. A high-resistance connection may pass current, but will act as a resistor, dropping voltage. The same way the ballast resistor in an old car (or Merc Inline Six!) works.

The problem with the internal harness could be as simple as a poor crimp on the end of the wire, or busted wires within. Sometimes you can wiggle the wire and see if that affects the resistance reading.

On your voltage loss from the external harness, I'd suspect the ign switch. Contacts corrode and then won't pass full voltage, or provide another high-resistance connection.

To get at the switch you'll have to pull apart the control box. Then, with the harness plugged in, measure battery voltage at the red (incoming) wire to engine ground. It should be same as battery voltage, if not there's a problem with that wire or connection at the plug.

Turn the key on and measure voltage at the red wire, and then at the white wire (the one going to pin "F" and the switchbox). There should be no difference in voltage between the "A" and "F" terminals on the ign switch, if so the switch contacts are bad.

You can also do resistance checks (with batt disconnected) from the switch to each pin in the external harness connector plug. You should get similar resistances for the wiring; if you find a wire with significantly higher resistance than the others, likely that's the problem.

Most likely you're gonna find a problem with the ign switch or the connections to the switch (which should be soldered).

HTH......ed

Man I appreciate all of the help you guys have given me! Thank you for your time! I've been trying to get this engine to spark for a month, but I want to do it the right way by diagnosing problems or eliminating possibilities! This is my first 6 cylinder merc and I'm finally making progress little by little and learning way more since this has been a long drawn out process! Thanks a lot! I'll keep everyone updated when I make progress!

Here is an excellent guide to troubleshooting that system, plus many others as well. Follow it to the letter and you will find the issue.

www.ebasicpower.com/downloads/cditech/CDI-Troubleshooting_Guide-MERCURY.pdf

Thanks, Ed-Mc. I had a spark issue this morning, and not knowing what else to do, I looked here. I figured it has come up before. Turns out, my switchboard had a bad connection.
Lake was mid to upper 70s and smooth water.

Will