Intermittent spark

From an older 550 service manual.
diode bank should be the same as the wire colors are the same.

His service manual should have the procedure for checking the diodes

So Svanslos,

You will have to locate the diode pack. 
My guess it will be close to the igniter

6 wire connector

3 brown/white wires 
1 light green wire
1 yellow/green wire
1 brown wire

disconnect the connector to the diode pack

set your meter to resistance

on the diode pack
you will place your red probe on the first brown/white terminal and black probe on the yellow/green terminal
what is the resistance?
reverse your probes--black probe on that brown/white terminal and red probe on the yellow/green teminial
what is your resistance?

next
move your probes to the next terminals over.

red probe on the brown/white terminal in the middle slot 
black probe on the brown terminal
what is your resistance?

reverse your probes
red probe on brown
black probe on brown/white
what is your resistance?


move your probes over to the last slot
red probe on brown/white
black probe on light green
what is your resistance?

reverse the probes
red probe on light green  terminal
black probe on brown/white
what is your resistance?

so your two readings with each slot should be different when the probes are reversed.
the two readings should never be the same.
there should be at least a difference of 10x between the two readings.

one direction maybe 10 ohms
reversed should be at least 100 ohms

if the readings are the same, you have a bad diode inside.
there are 3 diodes inside that diode pack.

   



 

 

Thanks for fantastic advice, just left the workshop to celebrate midsummer, will be back Monday with my spirit high and test the diodepack! Update will surely follow

H using this system on 74 900 and a 81 650, please search retrofit ignitions, the diodes are a fancy way of tying all the starter interlocks together to provide 12- to  the igniter, info on old post was obtained from classik forum, proof the diodes? ground out the black/yellow and the Br?/w, (other diagram show it as a black/ white, in the diode plug, the feed 12- to ignitor, see if it runs, wold put up a link, don’t know on ipad thx

Thanks Jewels I think we have established the ground is missing on the black/whitw