Ignition Question

[its55]

I’m investigating a starting issue with my ‘72 2002. It has the original ballast resistor and a (probably) 30 year old Lucas HP12 coil. 
 

The ballast resistor measures 1.1 ohms using my meter. Does anyone know if this is a good reading?
 

The coil primary measures 3.7 to 3.9 ohms. The secondary winding is measuring 7,300 ohms. Does anyone know if these are good readings?

 

I can’t find any specs on either one of these, ballast or coil. 

[John76]

What kind of starting issues are you having?

The 3.9 ohm coil you have may not need the ballast resistor

The original spec coil is a Bosch KW (black) with a primary resistance of about 1.9 ohms and used with a 0.9-ohm ballast resistor.

This is for a distributor using points and condenser. 

Did you check the condition of the relay that bypasses the resistor during cranking? If the relay is bad, you can get a very weak spark from the coil due to the lower voltage and added resistance during the starting process.

[its55]

4 hours ago, John76 said:

What kind of starting issues are you having?

The 3.9 ohm coil you have may not need the ballast resistor

The original spec coil is a Bosch KW (black) with a primary resistance of about 1.9 ohms and used with a 0.9-ohm ballast resistor.

This is for a distributor using points and condenser. 

Did you check the condition of the relay that bypasses the resistor during cranking? If the relay is bad, you can get a very weak spark from the coil due to the lower voltage and added resistance during the starting process.

Thanks! To clarify, my coil is not a “3.9 ohm coil”. 3.9 is the resistance I’m reading with tester. The car started up and ran fine until a couple of weeks ago. The other thing is that I recall seeing 3.2 ohms reading on this coil a few months ago.  My guess is that it was also a 1.9 ohm coil originally.  Seems that it is failing. Since the ballast is the original ballast, it’s 1.1 reading is higher than the original 0.9. So I should probably replace both. In the meantime I will also test the relay to make sure it’s ok. 

[its55]

I'm unable to locate another 0.9 ohm ballast resistor.  Would a 0.8 ohm be close enough?  

 

Amazon.com

WWW.AMAZON.COM

 

[jp5Touring]

eBay and Summit Racing have 0.9.  WTB ad would turn one up I would think.

No idea on the 0.8 

[Stevenc22]

I cant find the specs on the Lucs HP12, but If the primary resistance is over 3 ohms, you don't need a resistor. I would actually buy a Bosch or Beru blue coil and dump the resistor completely especially if you cant find a suitable resistor. 

 

Amazon.com: Empi Beru ZS 172 Blue Coil, 12 Volt Primary Resistance 3.5 Ohms VW Bug GHIA 1200-1600 : Automotive

WWW.AMAZON.COM

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Buy Empi Beru ZS 172 Blue Coil, 12 Volt Primary Resistance 3.5 Ohms VW Bug GHIA 1200-1600: Coils - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

 

Edited June 4 by Stevenc22

[John76]

39 minutes ago, its55 said:

I'm unable to locate another 0.9 ohm ballast resistor.  Would a 0.8 ohm be close enough?  

The factory spec for the external resistor is 0.6 - 1.0 ohms, so 0.8 is OK.

[its55]

1 hour ago, Stevenc22 said:

I cant find the specs on the Lucs HP12, but If the primary resistance is over 3 ohms, you don't need a resistor. I would actually buy a Bosch or Beru blue coil and dump the resistor completely especially if you cant find a suitable resistor. 

 

Amazon.com: Empi Beru ZS 172 Blue Coil, 12 Volt Primary Resistance 3.5 Ohms VW Bug GHIA 1200-1600 : Automotive

WWW.AMAZON.COM

---

Buy Empi Beru ZS 172 Blue Coil, 12 Volt Primary Resistance 3.5 Ohms VW Bug GHIA 1200-1600: Coils - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

 

Actually this is what I’ve decided to do!  also I tested the relay today and it’s good. Thanks to all for your help. 

Edited June 4 by its55

[jimk]

The ballast resistor is not in the circuit during cranking, only in the circuit after the ignition switch returns to the "run" position.

[John76]

39 minutes ago, jimk said:

The ballast resistor is not in the circuit during cranking,

True ... unless the relay is not switching.

[jimk]

24 minutes ago, John76 said:

True ... unless the relay is not switching.

The why is the OP chasing a new resistor?

[its55]

11 minutes ago, jimk said:

The why is the OP chasing a new resistor?

 

I was but I’m not anymore

[its55]

2 hours ago, jimk said:

The ballast resistor is not in the circuit during cranking, only in the circuit after the ignition switch returns to the "run" position.

 

Correct, however it can cause the startup to suddenly die if it’s a bad resistor. 

[jimk]

38 minutes ago, its55 said:

 

Correct, however it can cause the startup to suddenly die if it’s a bad resistor. 

Correct, but rarely that sensitive.

[its55]

6 minutes ago, jimk said:

Correct, but rarely that sensitive.

 

In any event, I'm getting rid of it!