Hella relay - normally open 12v for ignition circuit

[Agnelli]

128 wagon has an X1/9 electronic ignition. Recent symptom was a no start when hot. Diagnosis yielded 7 volts at the + side of the coil terminal and inconsistent voltage readings there and before the ballast resistor. Cleaned all the terminals and improved the situation. Then it occurred again on a hot day. Searched the forum (of course) discovering posts about how relaying the ignition can solve this. I should do this on my X as well, and will.

Plan to mount the relay next to the coil, hot to terminal 30 on the relay direct from the battery, triggered by the ignition lead. Results will be reported to you.

 

[carl]

My brother's BMW 2002 has some setup where the coil gets 12 volts on start and then reverts to the ballast resistor circuit providing 7 volts. This is from the factory. I think if you have a hot start problem that it's something not right.

 

[Dr.Jeff]

My brother's BMW 2002 has some setup where the coil gets 12 volts on start and then reverts to the ballast resistor circuit providing 7 volts.

Agree, that is very common on many vehicles of this era. I'm not sure how the relay will help difficult starting? Do you suspect the power wire to the coil is overheating, therefore increasing resistance and lowering conduction? If that is the case then I'd look at resolving that problem at its source, rather then attach a "band-aid" around it. But I might be misunderstanding the relay idea here.

 

[Agnelli]

The factory wiring diagram informs the + side to the coil is powered through the ballast resistor directly back to the ignition switch. Adding the relay to unload the ignition switch and provide full voltage and current to the ignition. Tested today, no issues after two hot starts.

 

[lookforjoe]

The factory wiring diagram informs the + side to the coil is powered through the ballast resistor directly back to the ignition switch. Adding the relay to unload the ignition switch and provide full voltage and current to the ignition. Tested today, no issues after two hot starts.

I had to do a similar thing when I still had the factory coil/ballast - but in my case it was due voltage drop in that circuit at idle. I rewired it through a relay, and end of problem.

 

[Dr.Jeff]

directly back to the ignition switch

I get it now, thanks.

I imagine if some of the ignition switch mods were done (e.g. decrease the large load items from drawing through the switch), and the BWM, as well as the other charging system upgrades that are somewhat common to do on the X1/9, then there might not be a problem with getting a full 12V through the switch to the ignition. But that's a lot of mods, so adding this relay makes sense. However some of those others are still good ideas in addition.