Sailon

Does anyone know what would cause the amp guage on a 1965 small block to flip 180 degrees each time the engine is started?

Each time the car is started the pointer alternates to pointing up and then pointing down. In either position it initially shows it is charging and then settles back to the proper 0 charge position. With out fail the pointer position flips 180 degrees on each start up.

0Willcox Corvette

The spindle that the needle is pressed on to has a round disc attached to it at the bottom. This disc is positive and negative charged. You have reversed the polarity of the disc inside the dash unit. This is not hard to do and can happen when you arch the wires at the alternator, or have a dead short in the car. Let me guess, the gauge reads correctly but upside down. It should still show charge and dis-charge.

How do you fix it? I’m just being honest here, I wrote a thread on this on the cprl thread years ago and I honestly don’t remember. I searched my laptop to see if I had a copy of this and maybe someone here can do a search for you.

Arching the wires to reverse the polarity again would be my first thought, but I don’t want you to fry the gauge. Let me see if I can figure this out again and email me direct at Willcoxcustomerservice@willcoxcorvette.c om

There is an easy fix but to much time has passed. I’ll put up a post on there tonight and maybe someone knows how to find it.

Willcox

Sailon

Willcox - Thanks for the response I sent you a separate email.

The really strange thing is that is doesn't just always point down, it alternates on each startup. So if I go out to the car and the guage is pointing up as it should, when I start the car the guage will flip to pointing down and stay that way when shut down. If I then restart the car, the guage will flip again and now be pointing up as it should again and will stay up when the car is shut down.

Sailon

I am still working on this one if anyone has any more ideas I would appreciate it.

Additional testing results starting with the guage pointing up:

If I just turn on the ignition, the guage remains pointing up and properly shows discharge.

If I turn on the wiper motors, radio, fan and rotate the headlights all
together, the guage remains up and properly shows discharge.

But if I turn on the lights or hit the starter the guage flips. So if the guage is pointing up and you hit the lights on with the brights on, the guage flips to pointing down and shows discharge. If you shut off the lights and turn back on the guage flips back to the proper up position and shows discharge.

Note: Once the car is running the amp guage no longer flips when you turn the headlights on and off.

Sailon

My amp meter continues to flip at each startup. Any ideas?

7T1vette

Pretty wierd.... I'm wondering if there is a ground wire/strap on one of the accessory systems which has separated and the ground for that circuit is back-flowing through another accessory circuit. I don't have a wiring diagram for a '65 to check it out, but an 'unusual' meter response is usually due to an 'unusual' wiring condition. If I can scour-up an electrical diagram, I'll search for a more specific possibility.

Sailon

Attached pls find 1965 wiring diagram images. Some rewiring has been done at the alternator and the original color coded wires have been replaced. It appears the repairs were done with the proper wire guage. I understand the voltage is stepped down before it goes to the amp meter but not sure where that occurs.

Fuse Panel


Engine Compartment


Instrument Panel

62Jeff

??

The Amp Meter on a 63-67 simply measures the voltage differential between the starter and the horn relay. You can remove the amp meter wiring from the back of the gauge, and with the car running measure voltage from one of the wires to ground, and then the other wire to ground, and I'd be very surprised if that value was stepped down.

But I'm open to being wrong.

I'm pretty sure when my Amp gauge was broken, I did that test and found > 12 volts at each wire.

wombvette

I could be that it just needs the damper replaced. The is a mechanism dampened to impeed fast movement of the needle. I am not a gauge expert, but I think they inject some non hardening material into the front needle bearing. You might want to call one of the gauge people.

SIXFOOTER

Hmmm, this one is a bit odd. OK, for the moment lets assume all your components are good: meter, relay, alt, regulator etc..
First place I would start is verifying all the connections on the affected circuit. Battery terminals, frame grounds, fuse links on horn relay, starter terminals. Verify the wires on the relay are on the correct terminals, this will mean maybe opening up wire harness to verify connection points and colors. Use a highliter on the drawing to document each one.
It looks like that the only time the gauge flips around is under very high current events (starting). one possibility is a slightly weak connection along the start circuit somewhere, which would force a portion of the start current thru the meter circuit. Annother possibility is a wire crossed on the relay. I have not opened up a gauge in a long time, wondering if the damper inside it is hosed up. Any chance you can swap in a gauge from a different source? Even a generic would work for a test.

SIXFOOTER

Correct, 12v to ground is what you should get, the amp gauge measures the voltage drop across a piece of wire of known resistance. All the current that runs the car with the exception of start current runs thru that wire. The higher the current (more stuff running) the higher the voltage drop across the wire and the more the meter deflection. This can be in either direction, with the engine running and stuff turned on the alternator should be charging the battery and supplying current for everythig and the curent will flow one direction. turn off the engine and the battery supplies current and the current goes the other direction on the same wire.

larrywalk

Sailon

First off THANKS for all the responses!

The posibility of the problem with the needle damping sounds very possible. The needle really bounces a lot even after startup. I hooked up a spare corvette amp meter I had but did not get any movement so I assume the amp meter must be bad. I removed it from the housing to see if I could check how it is dampened but the dial is riveted to the casing. Not sure if I carefully pry the dial off if the original rivets can be reused or if someone sells new rivets. I will try to locate a cheap amp meter and start tracing down the wires/grounds to make sure everything is hooked up correctly. I will also check to see that both wires that attach to the amp meter are hot. Thanks for all the suggestions I will let you know once I isolate the source of the problem.

JohnZ

The black/white wire goes directly to the screw terminal buss on the horn relay, and the black wire goes directly to the battery cable stud on the starter solenoid; both pass through the inboard multiple connector on the engine side of the fuse block - make sure there's no corrosion on the terminals inside that engine-side connector.

I'd be suspicious of the Bubba re-wiring at the voltage regulator.

7T1vette

The voltage differential that the ammeter is trying to measure should be in the millivolt range (small fractions of a volt); it is only measuring the voltage drop on that line, which is an indirect measurement of current flow. But, if a ground for one of the systems is bad and it tries to draw current from another cirucit, the drop in voltage on one side of that "shunt" line [or the other] could be a larger voltage drop than the meter normally sees. Thus, at start-up, the large swing one way; and after start-up, the large swing the other way. I would investigate the large (2 awg) ground cable from the starter to the frame. If that is weak, frayed, or corroded, you might get the symptoms you are seeing.

JohnZ

Midyears don't have a ground cable from the starter to the frame; the battery ground cable attaches directly to the outboard starter-to-engine mounting bolt (and both ends should be clean and shiny for good contact).

7T1vette

Thanks for the info. Then that would be a good place to check for good ground contact. All other 'major' ground connections should be checked, as well.

66since71

Bob, I'm just making an educated guess here, but it looks like the meter shunt is the wire from the starter solenoid battery lug to the horn relay. If you have replaced any part of that wire, it would lower the resistance of the shunt and could xxxxxxxxxxxxxxxxxx (edit.. no its the other way, less resitance and the meter is not driven as hard. JohnZ's point about corrsion and increased resistance would apply to the wire that is the shunt. Corrosion on the other wires, to and from the meter, would cause it to read lower than expected, not higher.)

The other possibilty might be that the 18B (black?) wire to the solenoid was attached to the wrong terminal on the solenoid. You would have had to have changed the size of the ring terminal, though... That would have removed the shunt from the circuit, all together, and the flip you're seeing might be a spike when the starter engages. Did the problem start following some starter work?

I'll call...

Harry

0Brian@CSofMD.com

I think that this is an easy one. If it is a real 65 amp gauge, take a look and you will see that it does not have the limiter pins on the face. I have seen lots of these type gauges on unmolested 1965 clusters. My understanding is that the pins were added some time in late 65 production but I am unable to verify when that was. The reason that your gauge is spinning is because the damping is not what it should be and the gauge is over reacting. The magnet is self centering at points that are 180 degrees apart. An additional tidbit for those that feel that the gauge is reading backwards, no need to reverse the wires. Just rotate the pointer until it is in the 6:00 position, gently remove and reinstall at 12:00 and it will work properly.

Sailon

Brian - You are correct I do not have limiter pins. I took a look at the ammeter guage on a 67 today and I see the limiter pins you are referring to. I will call you on Monday to discuss.

Forum Members - I am checking lots of possibilities and will post the resolution of this item as soon as I get there. Thanks!