Weird Voltmeter Readings - My '68 Dodge.

[SuperEd73]

Hello BITOGers,

I finally got around to installing an auxillary set of Sunpro gauges to supplement what's already buit-in the dash on my '68 Polara. I ran into a couple of problems however.

1) My voltmeter readings are a bit erratic at times. At idle the needle is very steady. Also when I rev the engine on the driveway the needle moves up and down as expected very smoothly. When I drive down the road at a steady cruise is when it gets weird. It centers around a nice normal 14v or so but the needle is very erratic. Lots of bouncing. I'm guessing some of that may be due to bumps in the road but this also happens on very smooth roads. For reference, I'm using a Pertronix Ignitor II ignition system with their Flame Thower II Super Coil with a hi-output alternator the old owner installed. I also made the voltmeter connection off of the Accessory fuse circuit under the dash. I'm thinking it's not really ok to have erratic voltage readings but the car seems to run ok. Radio works, lighting works, etc.

2) I couldn't get the plug out of the water pump housing to install the sending unit for the mechanical water temp gauge that was in the kit. I tried everything I could think of to remove it. Sanded down the area, tons of PB Blaster on the threads, tried whacking the plug a few times with a hammer to try and loosen up rust, tried removing it with engine hot and cold, etc. I also managed to destroy a neighbors "cheapie" breaker bar during the process. The plug basically has a square hole in it which a 3/8" extension fits into nicely. The factory electrical sender hole is too small for the mechanical gauge "bulb" to fit through. Anyway, I gave up on that one and I'll stick with the temp gauge in the dash.


3) At least my oil pressure gauge and the tachometer and lighting for all the gauges works nicely. Oil pressure at hot idle is around 30psi.

Anybody have any ideas regarding the voltmeter readings?

Thanks,

Ed B.

 

[JHZR2]

bad ground would be my first guess.

 

[newpassatt]

I would also check for a bad ground, especially where the voltage regulator is bolted to the fender or firewall (if memory serves); reomve the regulator & lightly sand to bare metal the area where the regulator makes contact with the body. You might also try a different connection for the volt meter, as the factory gauges have a regulator in the instrument panel that may be varying your readings. Hope this helps, it's been a long time since I've worked on these cars.

 

[AdRock]

Try tapping into the main power wire that goes to the fuse block. If the needle stays steady while tapped in there then the issue you're seeing now might be some corrosion on the fuse block connections.

The other thing I would do, just because I'm anal this way, would be to disconnect the battery, then disconnect every ground I can find and clean it with a wire brush and some contact cleaner.

You could also do some checking if you have a single piece wire long enough. Run the voltmeter connection directly to the pos. battery cable and see if the needle still jumps around.

 

[eljefino]

If you still have a mechanical regulator throw it in the trash. The replacement will wire up the same but be solid state like anything made since, well, a year after your car.

I guess you could idle the car and the alternator will be at 100% power (steady needle) and you could feel the regulator and it won't vibrate. Rev the engine with one hand and feel the reg, if it's vibrating it's a mechanical one.

 

[Canawler]

Check the wiring harness bulkhead connector where the main feed to and from the amp gauge goes thru. There will be corrosion.

 

[SuperEd73]

Thanks for the info! I'm pretty sure the bulkhead connector has never been touched in it's 41 years of use. Just from visual inspection I can see some oxidation on some of the contacts. I'm also going to try moving the positive lead for the voltmeter under the hood somewhere to bypass the bulkhead connector completely. Also is it a sure bet that any new voltage regulator I find would be solid state? Or are there still mechanical ones floating around?

Ed B.

 

[StevieC]

Originally Posted By: JHZR2
bad ground would be my first guess.
or bad charging regulator if still using the original external type, or bad connections to the alternator if your regular is internal.

 

[zrxkawboy]

Originally Posted By: Canawler
Check the wiring harness bulkhead connector where the main feed to and from the amp gauge goes thru. There will be corrosion.


Yes, our old Mopars are notorious for this.

 

[SuperEd73]

Well as recommended I disconnected the bulkhead connectors this morning before work. There's defintely some crud/oxidation on some of the contacts but nothing that looks severe or burnt thankfully. I now have the contact cleaner stuff so I'll be working on that later today along with cleaning up the contacts/ground on the voltage regulator.

Once again, thanks for the input!

Ed B.