'65 302 5-spd MSD-6A 1-wire alternator custom gauges

Starts and runs fine. As engine warms, gauges start dancing and voltage drops. Replaced instrument voltage regulator, alternator (w/ internal regulator), starter solenoid, ignition switch, and as many wire terminals as I could get at. Checked as many wires as I could for opens, grounds or resistance - all looked good.

When the radiator fan kicks in, it always start doing this. Sometimes when the lights are turned on it starts up. Somtimes it goes away by itself, especially when I'm troubleshooting.

Suggestions?

 

wow, you replaced just about everything that could cause it.

it seems to happen when the alternator goes under heavy load, are you running alot of gauges? if its not the alternator which it probably isnt since you replaced it it could be battery defect or you might have to end up rewiring the gauges

 

I like the "Somtimes it goes away by itself, especially when I'm troubleshooting." bit. Sounds familiar...lol.

The fan must be powered by solenoid.
The solenoid must be powered thru heavy wire near battery; like the #1 starter solenoid lug.

Engine must have heavy ground strap.

What do you mean the voltage drops? Does it drop at the battery terminal? Where does it drop?

 

Seeing as you've shotgunned the system it's time to start anew. Because it happens under load I'd double check grounding strap and make sure the belt isn't slipping.

 

All good stuff -

I replaced the radiator fan solenoid (forgot to mention it), but didn't really suspect it as the problem since the situation did occur prior to the engine getting warm enough to kick in the fan.

I tested the battery and also swapped one in to double check - no help.

I have a fairly standard gauge set up - Oil Pressure, Gas, Tach, Temp, Voltage. Their from Ford's classic lines and made by a top line supplier. They all worked fine for about 5 years.

Grounding strap and negative battery lead are possibilities I've not thoroughly checked. The battery cable terminal is good and the bolt to the block is tight. I'll test it on a megger or just swap in another to see if maybe there's an internal fault. Same for the grounding strap.

If and when I find this I'll post a reply.

 

Keep in mind a ground can be bad even though passes continuity check.

the engine to body strap must flow the total current of all body grounded devices. for example; if a 20amp radio replaces oem 1 amp radio the ground strap must be upgraded to pass the extra 19 amps.

same for the cluster ground wire; all current used in cluster must flow through the cluster ground wire.

double check wiring strategy for internally regulated alt.

Where does voltage drop? at batt posts?

 

The voltage drops at the battery posts, as well as at the gauges - hard to tell if it is the same drop as I only have one meter and the drop fluctuates. Understand about continuity not always being the best indicator of cable condition - fortunately I do have a meggar and can crank some amps through the cable to double check it. The existing battery cables are AWG 1 so pretty heavy duty. I'm thinking the grounding strap may have failed - I'll report back when I've checked it.

 

alt will affect post voltage depending on charging cycle.

does post volts drop below 12?

 

Where on the '65 should the engine ground be connected? It appears mine may have come away completely - can't find a pigtail dangling anywhere!

Thanks.

 

here is 64.5