ignition switch

Discuss all things Model T related.
Forum rules
If you need help logging in, or have question about how something works, use the Support forum located here Support Forum
Complete set of Forum Rules Forum Rules

Topic author
26gowjob
Posts: 1
Joined: Wed Jan 16, 2019 2:15 pm
First Name: jon
Last Name: pederson
Location: minneapolis MN

ignition switch

Post by 26gowjob » Thu Aug 08, 2019 8:24 pm

Is there somewhere that explains how the switch works?
I have a 26 , external DU4mag where generator was. Bought a switch to terminal harness. Using a couple of wiring diagrams (Ron Patterson, Texas T), I have power with switch lever at DIM to headlights and tail lights, On to headlights (bright?) and tail lights. Terminal 3 is hot all the time, as is 1, regardless of the key. key turned to BAT gives me power to Coil, which I don't need anymore. Key turned to MAG. no power at terminal.
With the external magneto, can I use the switch to run the lights, or do I just use the battery? Using a fuel pump, what terminal do I use so it's on only when engine is running?
Also, if I was factory original, where would the key be turned at starting? If the spark from the magneto post goes to the switch, it then goes to the coil? should the key be at MAG? Why do I have power to coil at BAT? Sorry to be so dense.
Thanks

User avatar

TRDxB2
Posts: 601
Joined: Tue Jan 08, 2019 4:56 pm
First Name: Frank
Last Name: Brandi
Location: Moline IL
Board Member Since: 2018

Re: ignition switch

Post by TRDxB2 » Thu Aug 08, 2019 9:59 pm

Here is a very nice and clear wiring diagram. You can see why terminal 1 & 3 are hot because they are connected to the battery ( 3 directly and 1 to the Amp meter to the switch and terminal 3 to the battery). The second photo shows whats inside the switch less the locking mechanism. Think of them function this way. The key operates turning left/right is used to select the power source and connects to the larger outer layer where the switch arm is used to select the lights choice. what is connected to terminal 3, the DU4mag or the mag output on the hogs head. Rest of you question depend on the voltage output of the DU4mag. Normally a fuel pump starts pumping just before the engine starts to turn over.
Attachments
Wiring diagram.png
SWITCH parts.jpg


BHarper
Posts: 88
Joined: Sun Jan 06, 2019 11:15 am
First Name: Bill
Last Name: Harper
Location: Keene, New Hampshire
MTFCA Number: 5414
MTFCA Life Member: YES
Board Member Since: 1999

Re: ignition switch

Post by BHarper » Thu Aug 08, 2019 11:18 pm

Hi Jon,
The "coil" terminal of the ignition switch receives power from which ever side the key is turned to, that being magneto or battery AS FORD BUILT IT.
For your application you could wire the fuel pump to "coil" and then turn the key to "BAT" to power the fuel pump.

You WILL need a seperate switch to kill (turn off) the DU-4. The Bosch DU-4 is live unless the the wire from its "Grounding Terminal" is actually grounded, not unlike the spark plug on a lawn mower.

842208.jpg

Note the Switch on the grounding wire.


100_5813a.jpg
The DU-4 on my '14 Metz. Note the skinny wire routed to the firewall for the ignition switch.


100_5815a.jpg
The radiator stay rod is wired to the back side of the switch screw to ground the magneto and thereby turn off the magneto's power.

100_5817a.jpg
The switch is simplicity itself. The brass strip hanging down turns the ignition ON. Swing the strip up and the magneto is grounded and the ignition is turned OFF.

Is your DU-4 a fixed type or is the timing adjustable? Metz used a fixed timing magneto.
Be diligent in wiring your car and good luck with your project, Bill

Post Reply Previous topicNext topic