Greetings friends!!! Been a while and I have been having lots of fun with kids and fishing and what not. But the Z car has been on a roll lately. I replaced the carbs with more carbs. and I finally have it back to running like a champ. In fact it is running and revving like it used to. Happy days! The peasants were happy!

Having said that. I took her for a spin the other day to keep fresh fuel running through the system and just generally keeping it running. Old cars hate to sit. As you all know. Important factoid: I keep my cars on a battery tender any time they are not running to preserve the batteries.

I pulled back into the drive way and light footed it and stalled it. After a bit of laughter, I tried to start it and had the annoying clicking of a dead battery. Which is strange as I keep the car on a battery tender all the time.

I hooked up the charger for about 2 hours and then the car started fine and I Pulled it in. Now the plot thickens.

So something was up. My thoughts are that the battery is about 5-6 years old and it is not unusual for a battery to be DOA after 5 years in the Houston heat. I left it on the battery tender all night and in the morning I disconnected it and it read 12.2 volts. Which seemed a tad low. But maybe not. So as I am oft to do, I started overthinking the issue and that leads to, (more times than not), spending money.

Since I was using the original starter that came with the car still (it had never let me down), I talked myself into thinking that the solenoid may be going bad (even though those are usually working, or not, no clicking issue), so now would be a rather handy time to replace that old grimy and dirty Z starter for a shiny new gear reduction starter :)

And since I bought a new starter I decided to go ahead and buy a new battery as well while I was at it. Surely that would solve the issue.

Well a week later and both were procured and installed. First let me say the gear reduction starter is the coolest sounding starter EVER. Sounds like you are about to start a 1000HP Big block Chevy. LOVE it. Car ran beautifully and started each time.

Fast forward to today.

I was going to drive in to work in the old gal to bless those in the NASA area with something besides a black or grey SUV to look at. Again this morning I disconnected the batter tender and it started just peachy. But I started to think about many things. There was no reason for my battery to really die before. I had replaced everything BUT the alternator.

So just to verify, with the car running, I whipped out my multimeter and checked the voltage of the battery. (I checked it by attaching the multimeter to the positive post and the negative post)

With the car at a rock steady 900 rpm, the battery read 12.3 volts. When I revved the engine it read 12.3 volts. It would flicker to 12.4 volts.

Now I am thinking my alternator may not be charging. It is my belief that a running car should put out north of 13 volts from the alternator. I am running an old MSA 60 amp alternator kit. My plans going forward are to start up the roadster and see what its alternator puts out while running as a sanity check. Any comments?

A good battery will be about 12.6-12.8 volts; 12.2 is very low and indicates it might not hold a charge. A good alternator will read 14-14.5 volts.

yup, that is what I am thinking. 12.3 volts while running is telling me my alternator is clearly not working. Well that is what I am thinking.

Don't overlook the winding wire. At the T plug on the back of the alt. One Sense wire, One Lamp wire. The Lamp wire needs good connection. I've had the spade connector get loose and lose conneciton. No charging.

19 minutes ago, Zedyone_kenobi said:

yup, that is what I am thinking. 12.3 volts while running is telling me my alternator is clearly not working. Well that is what I am thinking.

12.3 volts while running tells me that there is a problem. However, diagnosis is not complete. Have you verified the signals for the sense and ignition inputs? Those are the two wires going to the T plug on the back of the alternator.

NO I have not done that yet. I will pull that plug and check the quality of those fittings this evening. Had to run to work this morning despite my need to fiddle with cars.

What kinds of voltage signals should I be getting from those two wires?

47 minutes ago, Zedyone_kenobi said:

NO I have not done that yet. I will pull that plug and check the quality of those fittings this evening. Had to run to work this morning despite my need to fiddle with cars.

What kinds of voltage signals should I be getting from those two wires?

The signal wire should have battery voltage.

The ignition wire should have no voltage with the key in OFF, and it should have battery voltage with the key in ON.

I don't know 1971 but on a 1976 the charge lamp lights when the key is turned on aa a circuit and bulb check. It grounds through the alternator edit- external regulator then turns off when charging exceeds battery voltage.

It should be battery voltage with the key on and the plug unplugged.

Edited 2 hours ago2 hr by Zed Head

3 minutes ago, Zed Head said:

I don't know 1971 but on a 1976 the charge lamp lights when the key is turned on aa a circuit and bulb check. It grounds through the alternator then tunrs off when charging exceeds battery voltage.

It should be battery voltage with the key on and the plug unplugged.

There is no lamp on a 71. On the original 71 alternator, it would be a field wire and alternator neutral on the T plug going to the external VR. Since the car is modified, the field wire is jumpered to the ignition wire, and the neutral wire is jumpered to the battery wire.

I will report back to what I am getting out of these wires later this evening. I will also double check the connections and clean all terminals carefully. I will inspect all wires for fraying and damage. I may have a spare MSA alternator in my parts bin. I could just swap that in to see if I get a different result. Car has never really had any real electrical issue since I purchased it in 2008. Had a light stalk issue once, but that turned out to be a bad connection that Dave helped me troubleshoot. Good times.

My .02 cents on new alternators. Have it tested before you leave the parts store. I bought one and it blew the glass fuses, maybe not all of them but the car wouldn't crank and my gauges went limp. Ask the guys on here and found out it was "back charging"? Guys at the store were cocky but got alot nicer after it failed their test. Learned something new that day. 🙃