1966 Cadillac brake switch diode replacement

[Leonchandler]

I asked this question on an old thread yesterday but I'm making a new one here for visibility. Currently rewiring the dash on a 66 deville, and there's a little diode inline with the brake switch wiring, branching off to the transmission downshift solenoid. The diode is dead, no continuity in either direction. Does anyone know what size this diode is, or how much current is in the circuit? I don't want to just throw any old diode in there and have it blow again as soon as I start the car.
Thanks, Leon

[The Tassie Devil(le)]

The other topic referred to has been removed.

Bruce.

[klinebau]

A simple continuity test will not tell you if a diode is good or bad.  You need to use a multimeter which has a diode test function.  Perhaps you have done this, but didn't mention it.  I would hate for this issue to be mis-diagnosed and cause you to chase your tail.  There are other ways to to check the diode by looking at the resistance when the diode is forward-biased.

[Leonchandler]

Hi, thanks for the reply. I checked it using a DVOM with a diode function, and double checked with a small bulb and car battery hooked up to it in both polarities. The bulb didn't light. I'm adding some pictures, one of the diode itself, and two of the relevant parts of the wiring diagram highlighted, with the diode circled.
Leon

[Leonchandler]

I should add, power appears to come into the circuit via the violet wire at the directional switch, which comes from the main headlight switch. It was tricky getting it all in one photo with my crappy phone camera.

[Leonchandler]

Ah jeez, what am I talkin about  the power comes in from the dark green wire at the stop switch, striaght from the fuse box. That's what i get for reading diagrams while sleepy haha
Leon

[J. Gomez]

A diode allows the current to go through one way (arrows points the direction) while blocking it the opposite way. So if you have a +positive on the input of the arrow it will pass through on the other end.

You could use any of the most common diodes in the market such a 1N400X (X=1 â€" 7) these are rated at 1A, the differences is the reversed blocking voltage they would allow.  In looking at the diagram it seems it just supplies power to the thermistor (“T” symbol) so a 1N4001 should do it.

HTH

Good luck..!

[Leonchandler]

Hi, thanks for your input, you seem to know a fair amount about diodes. It's actually going to the transmission downshift solenoid, the routing is roughly dark green from fuse to stop switch, then white wire from stop switch to solenoid. Do you haven any idea how much current that downshift solenoid might be drawing?

[J. Gomez]

Hi, thanks for your input, you seem to know a fair amount about diodes. It's actually going to the transmission downshift solenoid, the routing is roughly dark green from fuse to stop switch, then white wire from stop switch to solenoid. Do you haven any idea how much current that downshift solenoid might be drawing?

Leon,

Unfortunately I do not. Solenoids can be heavy duty or light duty current devices, it all depends on the manufacture specs.

Maybe someone here can chime in if they know or have done testing on their ’66. You can also place your DVOM in “A” amp mode and connect the leads in series with the solenoid and active it to see the amp draw, I would guess it would be just a few ma. And by looking at the OEM diode on your picture I dough that one is rated more than 1A but looks can deceiving .

Good luck..!

[Leonchandler]

Unfortunately I do not. Solenoids can be heavy duty or light duty current devices, it all depends on the manufacture specs.

Fair enough, makes sense. Worst case, if no one here knows, I may just put the new harness back in without the diode and check the current across that gap with an ammeter to be extra safe like you say. It'd just be a lot easier to put it all together while I have the harness out of the car if possible.
Leon

[bcroe]

The stator solenoids I have checked for those years were about
18 ohms, so the current at 15V battery would be less than an amp. 
later years had cost reduced solenoids of only 10 ohms, good to
measure yours.  Even so a couple 1A diodes in parallel would be
very safe.

I use 1N4004 to 1N4007, nobody bothers to make 1N4001 diodes
(though they might be so labeled).  If not easily found maybe a
solar panel bypass diode (Eb*y) would cover it.  I buy them in
1000 lots, want a couple?  Bruce Roe

[Leonchandler]

Wow, this is exactly the information I was hoping for, thanks a million. There's a pretty decent electronics store near me, so no point sending diodes, the postage will probably cost more anyway. But thanks for the offer.
Leon