'71 - 911T no ignition spark at plugs

[HOFF+2]

Hello, I have a problem with my '71 - 911 and would appreciate any help as I'm seriously frustrated having spent the last 2 days trying to resolve the problem.

The car was running fine and as part of the restoration, I removed the motor/trans. Everything was cosmetically detailed, valve adjusted, new wires, cap, rotor, plugs etc. I reinstalled the assy. and it wouldn't start due to no spark at the plugs. The CDI box makes the correct sound, I've checked the coil resistance (per the Haynes manual) and all appears to be good. I was advised to try unconnecting the CDI unit and hook a test lead to the distributor input with a voltmeter and crank the motor over. I did this and there was no voltage (or pulse).

The only thing I can think of as a possibility for the problem it that I needed to replace the bakelite plastic connector piece at the rear of the CDI control panel (14pin) and its 'possible' that I put a wire or two in the incorrect spot in the connector block.

Is there a reference that indicates the correct color wires for this block? Also, any different feedback would be GREATLY appreciated!

Thank you very much! Mark

[Porboynz]

Well I think you are probably on the right track, you can PM me and I can send you a word doc I made up when I replaced the same plug on a 1972 911. Not sure how this will post when I copy and paste:

Engine Relay Panel Plug (female) Wiring Loom Description
1. Yellow Yellow Ignition switch
2. Green Green Oil Temp Sportmatic (spare)
3. Green Black (stripe) Green Black (dots) Oil Temp
4. Green Red(stripe) Green Red (dots) Oil Pressure
5. Green Yellow(stripe) Green Yellow(dots) Reverse light switch
6. Grey Grey Reverse light LHS plug
7. Grey Grey White(dots Cold start solenoid
8. Purple Black(stripe) Purple Black(dots) Tachometer
9. Brown Brown Earth
10. Black Black Rear Demister
11. Black White(stripe) Black White(dots) Rear Demister (spare)
12. Blue Blue Alternator charge light
13. Red Black(stripe) Red Ignition switch
14. Spare NA NA

Spare wire: Brown White(dots)


Engine Relay Panel Plug Description
1. Yellow Ignition switch
2. Green Oil Temp Sportmatic (spare)
3. Green Black Oil Temp
4. Green Red Oil Pressure
5. Green Yellow Reverse light switch
6. Grey Reverse light LHS plug
7. Grey Cold start solenoid
8. Purple Black Tachometer
9. Brown Earth
10. Black Rear Demister
11. Black White Rear Demister (spare)
12. Blue Alternator charge light
13. Red Black Ignition switch
14. Spare NA

Spare wire: Brown White(dots)

[Porboynz]

Not well it seems, lost all the spaces.

[Porboynz]

Lets try a screenshot instead:

[HOFF+2]

Thank you so very much for this information. It's exactly what I am looking for! Due to my work schedule I won't be able to get back to resolving the problem but will update accordingly. Again, many thanks Porboynz!

[BK911]

Points?

[HOFF+2]

OK...here's the update. I verified the 14 pin connection (both male and female) and all looked as it is meant to (albeit some of the wire colors were not 100% the same...but close enough). I reconnected everything and cranked it and still no spark. The CDI box I have was rebuilt by Specilized ECU Repair about a year and a half ago and is still under warranty (5 years!)...so I shipped it back to them for verification / repair. The points are brand new so I think things are good there. Hopefully the CDI box will be back to me in the coming days and will update accordingly. Again...very sincere thanks!

[Porboynz]

I posted the wrong plug details sorry, that's the loom plug that attaches to the fuse panel not the plug that joins the engine to the fuse panel. I was looking at it and wondering where the points connection was, duh! No wonder some colours did not match.

[Porboynz]

Here we go, here is the 14 pin engine plug that connects to the relay panel and the 3 pin plug that connects to the CDI. Don't forget the earth wire on the CDI.




And just for good measure I took this photo, yellow is pin #1 and the blank is pin #2




Good luck

[HOFF+2]

Thank you once again for this new information! After following the first communications wiring, I still did not have any spark. Having said that, I sent the ECU / CDI box out for to be tested / repaired. Well...I just this morning got a note back from them that my box tested out as it should...ie. no problem. They are shipping it back to me today. Based on your latest wiring diagram, I'll go back thru the 14 pin connector and rearrange it accordingly. When I removed the engine, I only replaced the female 14 pin bakelite block so the male portion on the panel itself should be fine. I'll give it a look as my work schedule permits and let you know! Again thank you very much!

Oh...the points are brand new as well and gapped correctly.

[HOFF+2]

More frustration! There must be a difference between our cars wiring. I have a total if (13) wires in the loom coming from the engine. Colors are...yellow, red, blue, black, brown, red/black, purple/black, grey/brown, grey/brown, blue/yellow, black, grey/red & green/red.

I tried looking at the Haynes book wiring diagram but found it useless! Not sure where to go from here?? Do you happen to know of a simplified diagram of the 14 pin connector? Again...that for your help!

[HOFF+2]

I'm super stumped with this 14 pin wiring connection (engine loom) on my 1971 - 911T!!! I have a total of 13 wires - yellow, red, blue, black, brown, red/black, grey/brown, grey/brown, blue/yellow, black, green/red, grey/red & purple/black. I have looked at ALL the info on this site and cannot find anything that replicates my 1971. The closest I found is the '72 but my harness does not have the same green wire combos and mine has 2 grey/brown wires that I have not seen in other diagrams. PLEASE...any help would be greatly appreciated....the car ran fine before I replaced the 14 pin baklite (female) piece.

[timmy2]

Your harness is the same as the '70 according to the wire colors you listed.
Probably a harness off the shelf before they made changes...
Here is where they need to go.
Looking from above with wires coming out below.
(Number two at the top is blank)




Sent from my iPhone using Tapatalk

[timmy2]

If you want to trace the wires
1. Yellow to starter solenoid
3. Black to oil temperature switch
4. green/red to oil pressure switch
5 & 6 grey/brown to reverse switch
7. Red/black to cold start temperature switch.(14 factory print)
8. grey/red to micro switch (15 factory print)
9. Purple/black to points signal at tach.
10. Blue green from ign coil + (not used on your car but in the older harnesses)
11. Blue to D+ of alt
12. Brown to alt ground
13. Black to DF of alt
14. Red to B+ of alt

SL 35 is the correct print for a 1970 for you to look at, Apparently they didn't post one for a '71 (SL 37)
Download it here:
http://members.rennlist.org/911pcars/WiringDiag.htm



Sent from my iPhone using Tapatalk

[HOFF+2]

timmy 2...this looks EXACTLY what my harness is set up for! The CDI unit will not be back until next Friday but in the meantime I'll re-connect the wires based on your information and verify with your tracing suggestions. I am so close to getting this 2 year restoration completed...when it wouldn't fire I was really bummed. I will update as the box arrives and hope for the best. Thank you again! Mark

[timmy2]

No Problem Mark, Happy to help.
Let me know if you need anything else.

[Porboynz]

It occurs to me that there are no connections in the 14 pin plug that would stop your spark. (well, a hard short on pin 9 will short the points to earth, but that's unlikely/unlucky) The rest of the wires are for the alternator and oil temp/pressure etc. The CDI is fed with a 3 pin plug, you need to have 12V on the centre red wire with the ignition on and if the CDI is whistling you do have power. (and earth) That leaves the connection to the points and the coil.

In your opening post you say: "I was advised to try unconnecting the CDI unit and hook a test lead to the distributor input with a voltmeter and crank the motor over. I did this and there was no voltage (or pulse)"

Well with the CDI unplugged there is no voltage to be had from the coil or the points so that's incorrect advice. The points simply provide an interrupted earth, not a voltage, and the coil gets its voltage from the CDI, lots of voltage!

I suggest you check both the points and the coil connections for continuity as follows with the ignition off and the CDI unplugged:
Black Points wire "C"; connect a test meter on low resistance range to the CDI plug end terminal and the other lead to earth. You should see continuity come and go as you manually open and close the points by hand. (if they are open, short them with a screwdriver, if the are closed, flick them open)
Blue Yellow Coil wire "A" connect a test meter on low resistance range to the CDI plug end terminal and the other lead to the coil terminal.

Warning; never short the coil wire to earth when the CDI is plugged in, that's an instant killer of CDI's. (this was an old school mechanic trick to stop an engine without turning off the ignition, but its deadly to CDI's)

If you do not have a meter, go buy one, they are cheap and very useful. Get one with a tone output for simple continuity testing. You can use a lamp and test leads but then you need 12V to check continuity.

My guess is you have your points incorrectly installed or connected as BK911 suggested, good luck fella.

[timmy2]

Very nice post and sound advice Porboynz.
Should help him troubleshoot very well.


Need a Wiring Harness? PM or Email me. Search harnesses in the classifieds

[HOFF+2]

Thanks to both of you again for your input on this issue. Last evening I rewired / connnected the 14 pin block following timmy2's drawing. All appears well now with that. After reading what each of the wire leads actually do, I too began to think that the 14 pin part likely would not cause the lack of spark problem. But...since I did replace the female bakelite part, it was very helpful to now know the wires are where they belong. Tonight, I tested the continuity per Porboynz suggestions and found that the resistance from the "A" to the coil wire feed had a 2.0 reading (meter resistance scale on 200) when connected it zeroed out when undone. The points were a little different story. Initially when connected per the test proceedure, if I shorted the points with a screwdriver, I got the restance reading of 3.8. BUT...when the points were in the 'closed' position, they did not show resistance. When I 'snapped' them they finally did. So I decided to replace the points and now to get the resistance of 3.8 I just need to manually open and close them. This all leads me to belive that since the motor has not been run for about 2 years, perhaps the points had oxidized and were not functioning properly? Only a guess but the proof in the pudding will be on Friday when the CDI unit arrives!! Thanks again to all!

[Porboynz]

Resolved?