CDI replacement, battery disconnect?

[89TRBO]

Is it necessary to disconnect the negative on the battery when replacing a CDI unit, and why? Thanks!

[Tyson Schmidt]

No.
There is no power to it with the ignition off.

[snbush67]

I’m not sure about the stock CDI but I’m pretty sure the MSD gets hooked up to a always hot. So if that’s the case then yes, disconnect the battery until the connections are all complete.

[RDM]

The wire to the CDI is not fused.

I would disconnect the battery for any electrical work, as some of the things you work around may be powered all the time and cause you a little excitement.

[Jonny H]

Originally Posted by RDM

The wire to the CDI is not fused.

I would disconnect the battery for any electrical work, as some of the things you work around may be powered all the time and cause you a little excitement.

Exactly this. I got asked this recently too, it’s car mechanic 101. It’s not necessarily about the job you are focussing on.

For example, if you dropped a tool onto the 3 fuses in the engine bay, they are all live with the ignition off and right next to the CDI unit.

[Schulisco]

For security reasons - absolutely!! No excuses!

A CDI can produce sparks up to 40.000volts - they can flash over distances up to 15inches/40cm! This if life threatening!



Trasnlated from Reparatur Bosch HKZ fόr Porsche 911 und 914/6

Thomas

[AndrewCologne]

The CDI unit itself – where we are talking about here – does not produce the 40.000 Volts, it's the coil and even here the engine must be running to make the inductive signal from the dizzy let the CDI get triggered.
When ignition key is off there's no current provided to the CDI and it can be easily disconnected, but as a rule of tumb im totally with RDM and Jonny to disconnect battery on all electrical work – even when just working in the engine compartment.

[RDM]

I had a long misadventure with the instruments because I didn't disconnect the battery. You just need to accidentally touch that one wire on the back of the clock to something sensitive to cause yourself endless troubles. Learned my lesson.