Install volt meter in place of ammeter wiring question

You do NOT need to make other changes to your wiring "to power the instrument cluster" or anything else. FUNCtionally all you need to do is follow the MAD article, and as posted above, connect the ammeter wiring.

BUT WHILE you are at it, it is EXTREMELY important to check your bulkhead connector and repair it as necessary.

(While the MAD article reduces much of the current through the bulkhead, it STILL must have a power feed into the interior, AND ignition, headlights, and other circuits OUT of the bulkhead)

ALSO check the voltage drop THROUGH the bulkhead to important circuits.

These include headlights and the switched ignition circuit

The path, for example, in the ignition circuit is---

battery,-- fusable link,-- through the bulkhead,-- through the ammeter circuit, --the ignition switch connector,-- through the switch-- and back OUT the ignition switch connector--and back OUT the bulkhead to the "dark blue" (normally) switched ignition wire which supplies your ignition, regulator, the alternator field on 70/ later vehicles, electric choke if used, and I believe the idle solenoid and distributor solenoid if used.

TO CHECK this circuit for drop, do the following

If you have a breaker point distributor, make sure the points are closed. Turn the key to "run" with engine off. Put your meter leads on the coil negative and ground. IF the voltage is close to battery, the points are open. Bump the engine until the voltage goes very low. The points are now drawing current.

NOW put your probes as follows: One directly on the battery positive post, and the other on the regulator IGN terminal, or the ballast resistor "key" side connection

What you are hoping for is a VERY low reading. Anything over .2V (two TENTHS of a volt) is getting a little high, and anything approaching or over 1/2 volt is WAY too much.

The higher this reading is, indicates some bad connection in the circuit path above.

(This is part of the reason that many of us use headlight relays. On my 67, I used an underhood relay/ fuse box out of a Voyager. I used the relays in this box to run ignition, alternator field/ regulator circuit, and two relays for the headlights, another for the fuel pump.)

Before I did a partial rewire of my 67, there was a ONE VOLT drop in the ignition circuit.

(This drop ALSO causes a one volt overcharge at the battery, because the regulator "thinks" the battery is low.)

All very good advice 67Dart273. Chasing voltage drop thorough out ones harness can drive you to drink because voltage drop is additive. In other words a few hundredths of a volt here and there add up. If you consider the several connections, and marginalized conductor size utilized in these antiques it is possible to have a half volt drop or more from battery though bulkhead connector to ignition switch back out to engine via bulkhead connector to ballast resistor, and over to coil to ground. Pardon me if I left out a few connections such as two big ones at battery terminals, my point is; a little less than a tenth of a volt at each connection adds up fast.

In a lighting circuit such as dome, or dash this would not matter a hoot, so its a little bit dimmer when the door opens, but to the voltage regulator, brain of charging system, it is a big deal. This is how over current problems occur in the electrical system leading to over loaded switches, lighting, battery charging, and sometimes melted conductors often at the bulkhead connecters.

Like 67Dart270 said; low voltage seen by voltage regulator causes alternator to output additional current to make up the difference The battery takes brunt of this imbalance as an over charge, which will boil it dry if not corrected.