Background - car is 75 c3 with L48 engine at around 100k was running fine but was having a problem with continued blown fuses for instrument lights. After looking at overall condition of wiring decided to replace all wiring and while at it install vintage air ac.
Car has been sitting idle for about 6 weeks but finally have the wiring and ac in. AC is not connected yet - waiting until confirmed engine and other electrics all ok.
Had previously fitted new distributor, alternator, spark plugs and wires and as mentioned running fine.
Tried starting car and no luck - if i remove the power from distributor the engine turns over fine but when I connect the power it is almost struggling just to turn over, every now and the it will sound like it is trying to start but then nothing. Checked battery which is fairly new and charged, even tried with jumper cables from my SUV but still not turning over easily - very sluggish.
Checked with spark plug tester and spark is intermittent either with a strong spark or nothing at all.
While I have been working on the car I have not been doing any work on the engine (or at least nothing I can remember) - did remove the distributor cap while installing some wiring but nothing else.
I have checked that all the spark plug wires are to the correct plugs.
I did have to remove the power steering pump to run the belt for the ac but not much else. Previously I had suspected that the harmonic balancer had been slipping but as I say the car was running fine before I started the rewiring. Also I have no record of whether the timing chain has ever been replaced.
Appreciate any help on solving this problem

 

Sounds to me like your maybe missing the grounding cable from the block to the engine. When this is missing the power will use anything to get a path to ground.
That could be the reason why sometimes you have spark and sometimes not. The ground cable usually goes from the block at the back end of the starter (attached with the support bracket) to the frame near the RF suspension (If you have an AIM it's shows the location there.)
Also check to ensure the distributor is getting 12v while the key is in the cranking position.

 

The cable OMF is talking about

 

Thanks for the responses - will check this out as I did have to remove the starter when I was putting the new wiring in so I may have screwed up the grounding cable

 

Checked ground wire and all good - checked distributor and in same place before I started the rewiring- will check my wiring again

 

May want to connect a jumper cable from the battery negative to the engine block and see if that makes any difference. With that you can determine if its a ground problem or not.

 

I thought the ground was good when I tested for continuity but tried the jumper cable to the block from the battery and definitely made a difference, also noted that the wire into the distributor did not appear to be well attached so corrected that. Now I have the engine turning over normally with a spark but still not starting - have tried some starter into the carb and every now and again it catches as if about to start then nothing. As far as I can tell the fuel pump seems okay but would that be the most likely culprit - will continue my investigations