What value diode do I use for my starter solinoidS? I have a solinod on my firewall as well on my starter. Thanks.

 

Why are you trying to prevent back feeding from the starter? Diodes are basically one-way check valves for current.

 

Diodes are also used for clamping the high kick-back voltage spike when the power is removed from a coil. They use them across the A/C compressor clutch, and they started using them on the starter relays when they started using computers to run the fuel injection.

Solenoids spec'd for the later model vehicles should already have the diode built in.

Here' some info on it.

https://en.wikipedia.org/wiki/Flyback_diode

This one should be plenty big enough.

https://www.radioshack.com/products/3-amp-400v-diodes

 

Thanks for the info, my Mallory Unilite distributor module crapped out on me recently, after doing some research on why this could happen, one reason was voltage spikes from relay coils (not good for electronic stuff like ignition modules........I have a 49 F1 truck and the only relays are for lights, accessories, starter and horn relay (would same 3amp200V diode work with the horn?). The relays for lights & acc. only draw 200ma so I'm using 1N4004 diodes.
Thanks

 

Seems like an odd usage of a diode, considering the Starter is only connected to the resy of the system when the ignition switch is in the START position. Perhaps your box crapping out is due to another source of voltage spiking under similar conditions? Alternator field maybe?

 

There can be a few things in the circuit when in start. The ignition system for one thing, you need spark for it to start when cranking. The fuel system if it has electric pumps. And usually the computer is hooked into the fuel system in some form or fashion.

I have actually got shocked on the old chrome aftermarket steering wheels with the chrome metal button. When I let up on the button I got a zap from the coil of the horn relay.

 

Could have been the alt. or reg. not sure how to track down any voltage spike issues from the charging circuit, all voltage checks done show normal readings, my grounds and connectors are clean and secure as well. I have installed a Mallory Circuit Guard between the coil and ignition module to stop voltage spikes......so far so good! Thanks guy's for your input.