No power to coil while cranking

Ulix

Ulix

True Classic
Hi folks,
On my 1974 X I get power to the coil with ignition on.
But turning the key further to the „start“ position, there is no power to the coil.

Any ideas?
I stared at the 1974 wiring diagram but couldn‘t figure it out.
I swapped the ignition switch out for a brand new one, with no change.

Thanks.
 
Hi Ulix,

I did some searching, but didn't find anything 74 specific that seemed similar. I did come across this discussion on a 1980, which could be very different wiring wise. In the pictures I saw it has the older style fuse block, so I figured I would post it as there could be enough similarity to give you some ideas.

Good luck.
 
Ulix said:
Hi folks,
On my 1974 X I get power to the coil with ignition on.
But turning the key further to the „start“ position, there is no power to the coil.

Any ideas?
I stared at the 1974 wiring diagram but couldn‘t figure it out.
I swapped the ignition switch out for a brand new one, with no change.

Thanks.
Click to expand...
The coil gets it's power when the ignition switch is in the on or cranking position. I'd check that the new switch power terminal maintains continuity when turned to the start position. That year also came with a seat belt interlock system but that should only impact the starter circuit.
 
Thanks for the help.
I found the problem.
My coil wire does not go straight to the coil, I use it to switch a relay that sends "good" power off the starter to the coil and my electric fuel pump.

However, the coil wire voltage drops from 13V to 9.5V as a I crank the starter. This 9.5V is not enough to trigger the relay, hence the voltage at the coil is 0V when the starter is engaged.

I measured the voltage at the starter directly and it is 9.5V while cranking. 10.3V at the battery while cranking.
I have high-torque starter on a 11:1 CR motor using a small wheelchair battery which is many years old.

I think a new battery will fix the problem.
 
One last post to wrap this up.
I found the real problem.
Somehow, the Bosch relay I installed ended up being a 24V relay rather than a 12V one. o_O
The 24V relay will engage at 12V but will disengage at 10V, where a 12V relay will disengage at 5V!

So, don't hesitate installing a relay in this spot, just use the correct one! 😁
 
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