Radio resets when brake pedal is applied!

[KFD]

Quick recap... I got a '77 280z with a fairly modern head unit. I press the brake, and the radio totally resets. I know the radio needs a constant 12v feed, and a switched 12v feed.

 

The 12V constant was wired through the cigarette lighter. I pulled the dash out yesterday as an assembly, drove the car today without a dash, but for kicks, I put the wire from the aftermarket unit into a hot side of the map light molex connector. Surprise surprise, step on the brake, radio resets! Now, the part that got me was that it doesn't reset every time I press the pedal. Brake and reverse lights work just fine, so that rules out the light switch being bad. The only thing I can think of is that the brake light is causing an excessive draw on the system. I'll report back with voltage at the battery when I get my hands on a multimeter to see if there are any shenanigans coming from the alternator...

 

I'm stumped! You guys got any ideas?

[datzenmike]

Get your supply from elsewhere on the fuse box.

[KFD]

That's the plan, but I am scratching my head as to WHY it's doing that. Next plan of attack is the turn signal switch that I just cleaned, and the headlight switch. The main beams currently don't work (even though the highs do, which prompted me to clean and rebuild the turn signal switch), and as I discovered this morning, flicking the headlight switch on causes the radio to reset. I will tear the headlight switch apart today and clean and rebuild it, and replace a check ball I lost the other day in the turn signal switch. I will report back with my findings. Anybody in need of a modern Kenwood head unit?

[datzenmike]

Seems like the voltage drops caused by swiching on a load is doing this. The hadlights get their power directly from the battery and not through the ignition. I would say clean your battery terminals and tighten them. Now find the ground cable where it bolts to the head and remove, clean and tighten it back on. Last remove, clean and tighten the positive cable where it bolts to the starter lug. I suspect a somewhat poor connection and a sudden load like the brakes or headlights isn't getting full battery power to keep the voltage up.

[Z-train]

Auto electrics 101-Stupid shit is ALMOST always a ground issue.

[KFD]

Thanks fellas. I will check that out after I get a few other issues sorted out. It's not a big concern of mine... I got an overheating issue taking up my time right now... I replaced the thermostat when Bcieplinsky had the car, I went to go meet one of my buddies yesterday at the top of the hill (Mulholland drive in Malibu), and the damn thing overheated on me... If you guys ever stop at the Trancas 76, they will charge you eighteen bucks to put half gallon of coolant in the radiator! Anyway, I will check grounds. It makes sense, considering the passenger's side headlight is dim (and now the main beams work after grounding the red/black wire). I got my work cut out for me. I just downloaded the EFI bible as well...

 

Thanks, fellas!

[DISLEXICDIME]

when my car did this it was because the alt was marginal at best and could barely supply enough voltage for every thing

[Dawa]

wtf, did the 77 z not come with a radio, thus having dedicated audio set up wires? why are you tapping from other sources?

i just googled 19077 280z manual, here is a source that came up

http://4moores.com/280z/files/Datsun%20280Z%20Service%20Manual.pdf

tap into the correct color wires, and power it as it should be. 

 

also, maybe there is air trapped in your coolant system. i had a 76 280z but not for very long so idk if they are similar 

to the ka24de but the ka is NOTORIOUS for trapping air in the coolant system whenever maintenance is done to the

system (new rad, thermostat, hoses, etc) 

 

try bleeding the system, its free. 

elevate the front of the car as high as safely possible, run the car with the rad cap off. let it come up to temp, turn on the 

heat full blast. the air is supposed to travel to the highest point, which is the rad filler neck. 

and by high as possible i mean really put that nose a few feet up in the air.

rear wheels chocked, ebrake on, trans in gear, and using jackstands, of course

[KFD]

I will try bleeding this system this weekend. I plan on flushing the radiator. The thing that is making my scratch my head now is that the temp gauge won't register under 3500 RPM! If you have the cap off (when I found out there was no thermostat in it!) coolant can be seen circulating. My guess is the waterpump impeller could be going, but nothing is leaking...

 

The Z had a radio originally. Like I say, this is an aftermarket unit... I'm chasing it down and the warm misfire (afm/ttime/coolant temp/fuel filter) issue as well. I'll keep you kids posted on my findings.

[datsunaholic]

wtf, did the 77 z not come with a radio, thus having dedicated audio set up wires? why are you tapping from other sources?

 

280Zs had a radio, but the radio harness doesn't have a constant +12V wire for your presets.  Typically folks hook that up to the first available source- the brake light switch feed, since it's always hot.  To add into the fun, a lot of radios nowadays use THAT wire as the main power, only switching on/off using the ACC wire.  Bass-ackwards, but there are reasons behind it (like ejecting the disc with the ignition off)

 

Since the brake lights are causing this, and EVERY place he hooked it to is fed by the same circuit (the BATT circuit, and likely all on the same fuse/fusible link), I'd suspect there's a pretty big voltage drop caused by the brake lights.  That's usually a corroded wire between the battery/fusible link/fuse that's acting like a resistor.  The problem will more than likely be at some connector.

 

  I have a radio that does the same thing, but only if the engine isn't running.   The radio on mine some reason won't work at less than 11.9V, and with the engine off I get 11.8V at the fuse panel IF I have the headlights on and the brakes engaged.  Running, I have over 13.2V so it doesn't happen.  I bet when this problem is solved, the brake lights will be brighter, because I doubt they're getting full voltage.

[KFD]

Thanks... I will check that out this weekend. I am chasing down the hot-wired fuel pump and other impressive shortcuts. I am leaning toward corroded connectors, myself. I think I might just run the +12v constant straight from the battery.

[datsunaholic]

At one time I had a basket case '77 280Z.  The wiring issues were legendary.  It did not help that the car had been stolen and partially stripped at one point.  I had to do quite a bit of rewiring just to get things like the turn signals working, since the center console was missing (the turn signals fed through the hazard switch in the console).  I finally got a console, only to find it was the wrong year and had different connectors.  Eventually found a right console and then had to undo all my bypasses.  That was about the only thing electrical that ever was permanently fixed- the thing went through fuel pump relays, ECUs, and air flow meters faster than oil changes, as well as a couple fuel pumps.  Likely was a case of a lot of missing grounds, which I didn't know at the time, but I ended up unloading the thing for a likewise basket case 510.  Carbs, I can figure out.

 

I feel sorry for anyone that might have gotten the car beyond the kid I traded it to.  I remember he thought it was great, only to have it start doing the same crap to him that it did to me.

[KFD]

Well I had some time last weekend to run through a few things. Instead of bumping this thread AND the hotwired pump thread, I'll give you guys the info here. This week, I replaced the waterpump and fan clutch (the shaft had a little wobble). Car runs cool. I got my hand on a mechanical regulator for now until I get a ZX or Monaco/Premeir alternator. I'll report back my findings on the brake pedal reset issue if the V/R did the trick, which to me would explain why there is no charge from the alternator to the battery.

 

As far as the fuel pump, I chased the wires down from that sweet lamp switch. It's a kill switch wired to break the circuit from the ballast resistor to the coil. So my fuel pump is fine.

 

Once the car can stay cool and charged, i have to figure out the misfire issue. I have the FI bible downloaded, but winzip doesn't want to play nice with the zip files for the other FSMs I got from Xenon S30. No big, I will break out the volt meter and start at the ECU.

 

I should post some photos...