12v source of power in 308

Anyone know if a good location of a 12v power source in the engine compartment of a 78 308? It seems that my Pertronix set up will not run correctly without a constant 12v of power. It seems that the previous wire from my starter/run switch is not at 12v all the time, more like 12v at start and 8v at run. I need to find a constant 12v, any thoughts?

 

Since no one has answered, I'll offer!

There is not one...no stock accessories are in the rear to require it!

A previous owner had to add a healthy power lead back there to power the MSDs in my car, since trashed!


So I'm afraid I have one, into a nice Power Distribution Block, unused, but you do not. Run a new one, from the fuse block or battery, thru the underfloor.

 

I'm glad you are on the trail to getting the ignition working!

 

Run a fused wire from your fuel pump which is below your coils. That is +12V with the key in start and run.

 

I am not sure you want to put any kind of load on your fuel pump circuit.
The starter receives 12v directly from the battery. This is your best bet.
Philip

 

your voltage should NEVER be below 12.5 volts in any circuit. this is an indication you have another problem. there is 12 volts to the starter, as there is to the little bulbs in the dash. check your battery voltage with the car cold and off. then start it, or in this case tuen on the ignition. you should have 12,5 volts or higher across the fuse blocks. any less indicated a clear problem. please post your voltmeter reading and perhaps we can help you narrow it down. Michael

 

Yea, the 'flaming fuel pump circuit' is the one I'd add constant load to...........

I was trying to offer a permanent solution. I did think about the 12V terminal at the starter.....maybe that would work.

 

On my 1984 QV, there is a conduit running under the middle of floor from the front end of the car to the rear. There is enough room left in the conduit to run one to possibly three new 10 gauge wires. The front of the conduit opens just under the battery compartment, there is a removable lid under the car, and you can easily access battery power, or from there other "stuff" in the front end. Use an electicians snake, run it through the conduit then tape the new wire as flat as you can to the snake and pul it through slowly.

At the rear, the conduit opens just behind the fire wall, and there is lots of room to run a wire up to where you need it.

Phil

 

An alternative to running a new line thru the existing duct from the front of the car:

Run a relay coil off of power to the ignition & ground. Connect a fused line between one of the relay's contacts & the starter's hot line from the battery. Use the other contact to power your circuit. Anytime the ignition has power, your circuit will have power.

BTW, further check that switched start/run line that drops to 8V, doesn't sound right. Should be usable. Either there's a really severe load, a poor connection, or you aren't connected to a direct line to the switch.

Could you be connected to the coil side of an ignition ballast resistor that's bypassed during starting to boost the coil voltage? (Haven't got a Carb'd wiring diagram handy.) If so, find the other end of the resistor & you should have a steady 12V you can use for your Pertronix.

 

Anthony -- (I'm with Michael on this one), the yellow wires at the "+" terminal of the coils should always be at the full +12V on a '78. But check the busbar/rivets on the back of the left fuseblock that connects the upper terminals of fuse #1, #2 and #3 -- the power food chain to the coils is: +12V comes down the azure (light blue) wire to the top of fuse #2, passes thru the rivets/busbar on the back of the fuseblock over to the top of fuse #3, and leaves the top of fuse #3 via the yellow wire which goes directly to the coils. If (during operation) you measure +12V at the top of fuse #2, but significantly less than +12V at the top of fuse #3 -- that would confirm that the rivets/busbar need help (this is the usual problem that drives all the fuseblock restoration/replacement projects here so it's a good idea to try to improve/augment those rivet/busbar connections on any carbed 308. In my case, running 2 Crane 3000s drew enough extra current to seriously melt that corner of the fuseblock in short order -- but all was OK after I soldered an auxillary busbar).

 

Oops, I transposed the positions (the yellow wire should be at the top of fuse #1 if never molested), but it doesn't change the situation -- you need a reliable, high-current capable connection between the tops of fuses #1, #2, and #3 (and should measure a reasonable +12V on the yellow wires at the coils when under load).

 

The Pertronix's hall effect sensors draw very little voltage (milamps)so using the fuel pump +12 is not a problem. I believe the coil gets 2 12v feeds from the starter relay. 1 feed is +12v in the "start" position and drops out in the run position. The 2nd feed is off in the "start" position and feeds +12v into the bypass resistor in the "run" position. So the voltage in the run position at the coils is somewhere around +8V.
So you need to either run a seperate wire from a 12V source to the pertronix's pick ups or you eliminate the bypass resistor and wire the "start and Run" wires together and attach them to the +12V on the coil and attach the pertronix wire there too. This is the way mine is set up.