Frequently Asked Questions

Short answer: A “GEN” light that stays on (especially glowing dull) when the alternator and regulator test fine is often a faulty dash ground causing a ground loop through the GEN bulb. Try a temporary ground — a clip lead or wire from the back of the cluster to bare metal — and see if the light goes out.

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Short answer: The backup-lamp switch on a manual-transmission 1968 is adjusted per the 1968 Pontiac Service Manual (pg 12-22). (Automatics use the neutralizer-switch adjustment instead.)

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Short answer: Factory Firebirds used a resistance wire to the coil, not a separate ballast resistor — you should never run both. If your coil has internal resistance, use neither an external resistor nor a resistance wire.

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Short answer: A brake light that stays on after a master-cylinder job is almost always the brake-light switch on the pedal assembly under the dash — it usually just needs a small adjustment so the returning pedal opens the switch. Since tapping the pedal turns the lights off, only a minor adjustment should be needed.

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Short answer: You can order a wiring diagram (which covers the dash printed circuit board) from Classic Industries or most other restoration catalogs — about $7 for a ~20-page set.

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Bulletin 68-I-31 — Pontiac Motor Division Dealer Service Information Bulletin, Section 1B, dated December 14, 1967. Attention: Service Manager.

Subject: 1968 ATC Wiring Harness Revision.

Short answer: Several wire color codes in the 1968 Pontiac Automatic Temperature Control (ATC) harness have been changed. Refer to the updated wiring schematic on the reverse side of the bulletin (reproduced in the scan below) when servicing cars with the new harness. Also correct Step 6 under “Adjust Door Link” on page 1B-2 of the 1968 Service Manual.

Short answer: Here’s the 1968 engine-compartment wiring schematic, from the 1968 Pontiac Service Manual.

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Short answer: When the fuel gauge reads always-full and the temp gauge always-cold but oil and alternator work, it’s usually not a cluster ground — the Rally cluster’s grounds only serve the lights and indicators; the gauge circuits ground at their sending units. Since the oil gauge works, you have +12 V to all the gauges (shared feed on pin 10, pink wires), so each dead gauge has one of four faults: a broken wire to the sender, a bad sender, a bad sender ground, or a bad gauge.

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Short answer: On a 1967–68, converting from idiot lights to a Rally gauge cluster is not a simple pin swap. You can get the oil and water gauges to read fairly easily, but making the ammeter work requires reworking the harnesses all the way back to the voltage regulator — the Rally setup has extra wires the idiot-light cars don’t.

Realistically you either re-pin and add wiring to the bulkhead connector, forward-lamp harness, and dash harness, or buy the correct harnesses. (1969 is far easier.)

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Short answer: On a column-shift automatic, the backup-light switch and the neutral-safety switch are combined in one housing. The purple wires are the neutral-safety circuit; the thinner wires are the backup-light circuit.

To troubleshoot: check for power going into and out of the switch, wiggle the shifter while you test, and jump the connector to confirm the backup bulbs work on their own.

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Short answer: The optional clock mounted on the console, ahead of the shifter — the correct opening is somewhat oblong with two mounting holes (a large round hole means a previous owner butchered it). If your build sheet calls for gauges and a clock, look for a console clock (Hemmings, Ames; working ones can be pricey).

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Short answer: Headlights-on making the indicators glow dim and the gas gauge drop is almost always a bad dash ground (sometimes a shorted instrument lamp). The dash gauges and lights ground through a thin metal strip sandwiched between the radio and the dash — if the radio’s been removed/changed or the connection is loose, the dash goes haywire.

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Short answer: The power windows aren’t on a regular fuse — they run through a circuit breaker under the driver’s-side cowl (kick) panel. Check that first.

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Short answer: Strange tail-light behavior after a bulb change is very often the wrong bulb in the wrong socket — typically a single-filament 1156 installed where a dual-filament 1157 belongs. Swap in the correct bulb and the odd symptoms usually clear up.

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Short answer: Details on replacing the dash cluster (including the wiring considerations) are collected in the Interior FAQs — Dash section: FGF Interior FAQ — Dash.

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Short answer: The 12-gauge purple wire (from the starter switch, through the firewall plug) goes to the “S” terminal, which actuates the starter solenoid.

The “R” terminal is a relay contact that, while cranking, feeds a direct path to the ignition coil’s positive terminal — this maximizes coil voltage for a hotter spark while the starter loads (and drops) the system. When the engine starts and the switch is released, “R” disconnects and the coil runs normally through the ignition switch and resistance wire.

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Short answer: A solenoid and starter wire running too close to the exhaust will cause hot-start problems — re-route the wire. But it shouldn’t affect how the engine runs unless the insulation has burned through and is shorting out.

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