Possibly but consider this... Using figures from my 1975 GE miniature lamp catalog, the stock HL breaker system is supping approx 10A with brakes applied and lights on(HL use a separate breaker in sw).. This figure includes park, side marker, dash lights(W/radio), license & hi/lo filaments for tail lamps... Adding four 1157 in the back results in an additional 10.76A, or slightly more than double of original design... I dunno the rating of HL breaker for that circuit but I doubt it's more than 20-25A, time and usage(especially after cycled a few times) will degrade the breakers capacity...
Here's another thought (just a thought), Install LEDs (194 equivalent) to the side-marker lights and instrument cluster. I don't expect that to cure the problem, but it may help, since they draw less current than the incandescent bulbs. I hate LEDs in tail lights though. They don't look right or flash right.
Another possibility would be disable the center brake lights, that'd reduce current draw by 4.2A... Draw for a 194 is .24A or almost 1A total... Still with the wiring issues that plague the early Mav/Comet firewall connector/fuse panel, running a separate supply would be beneficial to the electrical system... With brake/signal lamps off the system, the HL breaker only has to supply approx 5.8A, even one that's a little tired should be happy......
installing a relay like Krazy suggested is a good idea. the whole point of relays is to use low amp current to control a high amp circuit via electromagnetism. (much like the solenoid switch mounted with starters) so you can still run all your tail lights and not use over the factory specified current flow.
Here is a tech article about using relays, this is for using them with a sequencer but could be modified to just use tail lights http://mmb.maverick.to/resources/how-to-install-a-tail-light-sequencer-using-relays.21/
Thanks for all the responses and suggestions to this thread. I've bought 2 30 amp relays that I think I'll just install and try to fix the problem once and for all. It seems to be getting slightly worse so I think it would be best not to keep triggering the breaker. I'll go buy some 100ft of wire and start wiring the relays in, but I was just curious. If everything's installed already in the car already, how would you guys suggest to run the wire from the battery to the trunk?
I'm guessing you can find a opening in the firewall, then follow same route as factory down driver side sill plate into trunk... OR if you prefer, route down passenger side under sill plate into trunk, that's a straight shot... I'm sure your HL sw, signal sw & brake lamp sw will thank you.... A side benefit will be you can wire up a light that operates with trunk open... Using a switched source was mentioned but I wouldn't recommend it as brake lamps would be inoperative unless ign was on...
U didn't mention a fuse in this modification. Fuse/breaker close to the battery/pwr source as possible. Depending on wire gauge, length and load to be carried will determine what capacity fuse/breaker is necessary. Not knowing ur knowledge on electrical mod's -this is just a reminder.
Well I figured I'd just put a 30A-40A inline fuse in the engine compartment right after it comes off the battery so that I don't need to worry about mounting it and hiding it in the passenger compartment. (Might give easier access too! ) I haven't done all the equations yet to figure out the maximum current flow but in my mind it seems like that should cover the brake lights just fine. Does that sound about right?
Use at least 25A fuse and wire to carry at least 30A... What no one thinks of is at the instant voltage is applied to a cold filament, current is at least double to maybe 3x operating, this is why most lighting circuits use a circuit breaker as it takes a constant over current to trip it... Auto fuses won't blow instantly so double amperage is probably OK... At 2.1A each, the brake/signal filaments will total 12.6A...
I ran into this same problem with my T-bird/Shelby lights, added up to almost 10 amps to the current draw when the brake lights came on. I took apart the headlight switch and jumpered out the internal circuit breakers with buss wire. I then added heavier gauge wire from the switch socket to three heavier circuit breakers mounted under the dash. One breaker each for the brake lights, marker lights, and headlights. A bigger alternator definitely helps, too. Considering the original alternator was rated at something like 35 amps it probably only put out about 15 amps at idle. Now consider it's nighttime and all of your lights are on, the radio's on, maybe even the heater, the ignition is firing away. And you have to stop for a red light with your foot on the brake pedal (10 amps!) and the engine idles down....
