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ray_mcavoy · 11-25-2022, 09:24 PM

You're welcome!

Yes, the "brake" warning light down in the lower left along with the smaller "brake" light (next to the seatbelt light) in the bottom of the fuel gauge face is factory original. This was another one of those subtle changes they made over the years.

The "brake" light started off down in the lower/left corner on gauge & warning light clusters. But when a clock was added (or a tach which used that lower left for a fuel gauge), the "brake" light had to be re-located to a different spot. For 73-76 they put it in the bottom of the speedometer face. Then for late 76 or 77, moved it to the bottom of the fuel gauge (or tach) face. And finally for 78 they eliminated the "brake" light in the lower/left (for all cluster styles) and made the one at the bottom of the fuel gauge (or tach) the standard location. Since 77 was right in that transition period, those gauge clusters ended up with the 2 "brake" light provisions.

I don't think 77 originally had the "brake" warning light wired up to the parking brake (that came along in later years). Instead, it's just connected to the pressure differential switch in the proportioning valve. So try temporarily unplugging the connector from the proportioning valve. If that allows the "brake" light to go out, the switch is bad (assuming you don't have a brake pressure issue that has tripped the switch).

But if the light stays on, check the wire (tan if I remember correctly) to see if it's shorted to ground. Look for any place where the insulation may be chafed and allowing the wire to touch metal or for any place where the wire might have gotten pinched under a bolt/bracket/etc. The switch is on the ground side of the circuit (completes the circuit to ground when closed) so the wire being shorted to ground would cause the light to stay on.

11-25-2022, 09:24 PM	#4
ray_mcavoy Registered User Join Date: Nov 2009 Location: Sherman, ME Posts: 2,355	Re: 1977 gauge cluster questions You're welcome! Yes, the "brake" warning light down in the lower left along with the smaller "brake" light (next to the seatbelt light) in the bottom of the fuel gauge face is factory original. This was another one of those subtle changes they made over the years. The "brake" light started off down in the lower/left corner on gauge & warning light clusters. But when a clock was added (or a tach which used that lower left for a fuel gauge), the "brake" light had to be re-located to a different spot. For 73-76 they put it in the bottom of the speedometer face. Then for late 76 or 77, moved it to the bottom of the fuel gauge (or tach) face. And finally for 78 they eliminated the "brake" light in the lower/left (for all cluster styles) and made the one at the bottom of the fuel gauge (or tach) the standard location. Since 77 was right in that transition period, those gauge clusters ended up with the 2 "brake" light provisions. I don't think 77 originally had the "brake" warning light wired up to the parking brake (that came along in later years). Instead, it's just connected to the pressure differential switch in the proportioning valve. So try temporarily unplugging the connector from the proportioning valve. If that allows the "brake" light to go out, the switch is bad (assuming you don't have a brake pressure issue that has tripped the switch). But if the light stays on, check the wire (tan if I remember correctly) to see if it's shorted to ground. Look for any place where the insulation may be chafed and allowing the wire to touch metal or for any place where the wire might have gotten pinched under a bolt/bracket/etc. The switch is on the ground side of the circuit (completes the circuit to ground when closed) so the wire being shorted to ground would cause the light to stay on.