What would cause my brake light and gauge lights fuse to blow? I put the car in reverse and it blew! As you can see in my picture, I upgraded to the blade style fuse box. The fuse missing is the 20 amp that keeps blowing. The car is a ‘73 240z.

I had an alternator that popped mine. It was a reman from a chain store. The smart electrical guys on here said it was "back charging". Took it back, they tested it and it showed BAD. Gave me another one and so far so good.

Edited October 19, 2025Oct 19 by siteunseen

Did the problem show up immediately after the new fuse box? More detail might help. The wiring diagram doesn't seem to show any connection between the reverse lamp circuit and the brake or gauge lights. They do all have a fuse though. The fuse box seems like the common element.

Also, the FSM shows a different wiring scheme for automatic compared to manual. Body Electrical chapter. Accessory Relay and Inhibitor Switch.

p.s. do the reverse lights work? They're on a separate fuse right? Can't find an illustration of the fuse box.

Edited October 20, 2025Oct 20 by Zed Head

p.s. 2 - check the reverse light sockets to see if they're melted and shorting to ground. I had one do that. Not reverse but a tail light socket. They get crusty and resistive and produce heat.

I’ve had the new fuse box for several years before this problem happened. My reverse lights work.

The problem is intermittent. Also what is the proper route for the choke cables?

Put a meter from the fuse exit to ground in continuity/resistance mode and see when the circuit goes open. Wiggle that nest of wires around. If the fuse is blowing it must be because that wire to the switch and lights is shorting to ground. Could be at the switch ( a bad switch) or after it.

Or crawl under the car and test the pins on the switch to see if they're shorting to ground when you put it in reverse.

Check the wiring diagram to see if any of the things after the switch are shorting to gorund. You didn't say auto or manual.

18 hours ago, Zed Head said:

a different wiring scheme for automatic compared to manual.

18 hours ago, Zed Head said:

check the reverse light sockets to see if they're melted and shorting to ground.

The pic shows a stick shift in the console so I assume it’s manual. Possibly a chaffed cable touching metal.

Edited October 21, 2025Oct 21 by Yarb

That is true, but it could have been converted from auto. I'm just throwing out bread crumbs. Something is drawing too much current. Find the thing.