[T3] Electrical questions

[Sean Bartnik]

Hi all,
This is a cross-post from the Samba but I wanted to get a read on this from the great minds here.

Just as a bit of background, not long ago I put in Cibie H4 55W/60W halogen headlights with relays.  Over the last few months I suspect the battery had become slightly discharged just from a lot of short-trip city driving.  Last time I measured anything it was showing about 6.13V which is a bit low.  The other day I drove to my office parking garage to aim the new headlights.  Left engine idling while aiming them, then took a drive for ~20 min to run an errand.  Came out of the shop and the Eggcrate wouldn’t start.  It was cranking fine but no sign of ignition.  I did not have a meter with me to check voltage at coil terminal 15 while cranking but I was guessing that the idling while aiming the headlights might have put my battery below where it needed to be.

Luckily I was parked somewhere I could push-start the car myself, which I did and it fired right up.  Once I made it home I put the battery on the charger and it did indeed need a charge.

Today I decided to poke around and do some voltage drop testing.  And here’s where we get into the Samba post:
I’d love to get some input on these findings:

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Spent some time today checking out the electrical system to make sure everything was in order, and trying to eliminate or reduce some previously measured voltage drops.

So today with fully charged battery (6.28V) I measured voltage drop from the + terminal of the battery to:

*With ignition off*
Voltage Regulator B+ terminal: 0.00V
Lug on fuse box were the B+ wire comes in: 0.00V

*With ignition switched on*
Voltage regulator B+ terminal: 0.03V
Headlight switch terminal 30 in from VR: 0.09V
Headlight switch terminal 30 out to fuse box: 0.10V
Fuse box terminal 30 in: 0.28V
At fuse box terminal for 15 wire from ig. switch: 0.29V
At fuse box terminal for 15 wire to coil: 0.30V
At coil terminal 15: 0.56V.

So I was losing over half a volt from battery to coil with ignition on.  This may have been my starting problem the other day as the battery was slightly discharged (6.13V) to start with before idling with headlights on to set the aim. When cranking the voltage at coil terminal 15 could have easily dropped to below 4.8V and no sparky.

So I pulled the fusebox down and started poking around, finally decided to hell with it and pulled the whole fusebox out.  Hit everything in the fusebox with De-Oxit.  Measured resistance across the bus bars that join certain neighboring fuses, 0 ohms.  Put fuses in and measured resistance across the fuses.  0 ohms.

Hit some of the wire terminals hanging in the car with De-Oxit.  Some of them were a bit loose on their spades so I tightened them up with pliers.  Also pulled the headlight switch and hit those terminals with De-Oxit.  Notably the terminals for the big red wires to headlight switch and from headlight switch to fuse box were a little loose.  Clamped them down a bit.  

Pulled the coil and cleaned up terminals 15 and 1 with sandpaper and De-Oxit.  Clamped the terminal 15 wire down a bit too as it was somewhat loose.

Measured the resistance of the coil wire from fusebox to the engine compartment and it was only 0.3 ohms.  For reference, my meter reads 0.2 ohms when you connect the two meter leads together. Ol' Crispy is pretty non-crispy in my car, thankfully.

Put the fuse box back together, didn't leave out any wires and everything seems to work.  This time I measured voltage drop from battery + as follows (ignition ON):
@ Fuse box where 30 comes in from H/L switch: 0.11V (was 0.28V)
@ fuse box where blk wire comes in from ig. switch: 0.15V (was 0.29V)
@ fuse box where blk wire goes to coil: 0.15V (was 0.30V)
@ coil: 0.33V (was 0.56V).

So clearly things are better now.  Can anyone with experience advise as to whether these are reasonable voltage drops?

Then I connected my meter to D+ terminal on voltage regulator and the other lead to battery ground.  Fired up the engine and not long after generator cut-in, I was showing a good 7.5V on this lead not too far above idle.  

However when I switched my meter over to terminal B+ on the VR, I was getting around 6.5V at idle up to about 7.01V at max speed.  With headlights on that dropped to around 6.75V at max speed.

I would love to see 7.5V out of the voltage regulator.  Is there a good reason why I shouldn't attempt to make that adjustment?  I worry that I don't fully understand the relationship between charging voltage and charging current and therefore I'm hesitant to mess with it without fully understanding it.

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Thanks!
-Sean
’65 Squareback (formerly Keith Park’s)