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slodat

"Hot Start" relay

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I have done this simple mod to every Datto I own. Reason is the starter solenoid power goes through the ignition switch's start contacts. This circuit drops some of the much needed battery voltage, especially in 30+ year old Dattos. This can ultimately mean there is not sufficient voltage to pull the starter solenoid all the way in and make contact.

 

Pick up a Bosch style 30/40a 12v relay. They are everywhere and are very cheap if you know where to buy them. I bought a 10 pack with wiring harnesses for ~$25 on eBay.

 

Wiring:

 

30 - 12v from battery (fuse this line)

87 - starter solenoid terminal

85 - original wire from starter solenoid terminal

86 - ground

 

Now, when you turn the ignition switch to the start position, the coil in the relay is energized from the ignition switch. This connects the starter solenoid terminal directly to full battery voltage.

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interrupt the '85' wire from the starter solenoid and run it to a hidden toggle switch. This will act as a starter kill switch. Also, install an alarm. :D

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Thanks for the how-to...

This can also be used for the headlight conversion as well as other things you want to straight wire around the switch, like heater blower and wipers!:)

 

best alarm devised yet: trunk monkey!:rolleyes:

Yours must have had a hangover that day bleach!

We told you not to let it drink beer!:D

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That is true, relays have a lot of uses in our old Dattos. Think of it as an electrically controlled switch. One of the best improvements I've made to my 510 was replacing the stock headlight relay with Bosch relays on both high and low beams. They are also great on the horn, dome light, you get the idea.

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Figure I'd share some info I found out the other day from a friend of mine. The engine bay fusebox in Intrepids have a shit load of relays in them. Only downside is that they don't have any mounting tabs. Not that big a deal to me tho, from one Intrepid I walked out with about 10 relays.

 

Also, is there a comprehensive list about Datsuns and relays? I know of this one, and the headlight one. I don't much know about any of the other ones.

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The 720s have a 15 fuse box with at least two relays (3 in US) clipped to it, and two more above the pass kick panel for auto choke and electric fuel pump.

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so i googled Bosch style 30/40a 12v relay and after all for sale shit . was the ratsun forum link. now thats cool!!! also this is great thank you for posting this .I have had a problem startig my dime sometimes it took 8or9 trys :blink:before it would kick now it starts like a new car :eek:

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headlightstartrelay.jpg

 

I'm going to do this on my truck, and leave the 30A fuse out. It's not ready to start, but I want to test the rest of the electrics. :D

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nice writeup slodat, I will be doing this now when I redo the headlight wiring I did in Alabama :D

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running from the factory ignition switch you can just reuse the factory wiring and match that size, if it can power a starter it can engage a relay no problem. on the other side i would just go bigger than whatever the stock junk was and call it good, unless you want to get fancy and do the math :P http://www.powerstream.com/Wire_Size.htm

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I ran a 12 gauge wire from the battery to the relay and from the relay to the solenoid. 14 gauge wire for all the trigger wires. I even wired it through my starter interlock switch so it only makes contact in Park and Neutral. Other than a solenoid issue (that I knew about beforehand...) it works great. No second guessing the voltage at my solenoid (which I recommend everyone check prior to install, just to have a baseline). Mine was 9.9 volts at the solenoid in START prior to install...!

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Here is a link I often look at for wiring Relays.

 

Relay Wiring

 

The use of a quenching diode is a good idea to prevent feedback in the curcuit after the circuit is shut off.

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interrupt the '85' wire from the starter solenoid and run it to a hidden toggle switch. This will act as a starter kill switch. Also, install an alarm. biggrin.gif

Interupt the wire before or after the fuse?

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Interupt the wire before or after the fuse?

 

It doesnt matter as long as the switch goes back to the same spot in the circuit. There is nothing to "blow" when using a toggle switch so there doesnt need to be a fuse... if you interrupt the circuit prior to the fuse, when you wire in the switch it needs to be completed prior to the fuse. If you interrupt after the fuse, you need to complete it after the fuse. You wouldnt want to bypass the fuse when your toggle switch circuit is closed. 

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Sweet, Ive had to push start my truck some days because the starter refuses to engage. Hopefully I can get this relay in without a hitch.

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I like the smaller modern relay you show. I have done this using a Ford style starter relay and have bought several rigs that already had it done with a Ford type. They worked well but larger and heavier than the ones you show

 

misw3_is_zps63bf0f00.jpeg

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I hooked my relay up today . It did not work. Mine is the Pico brand.

I switched #87 to 87A and it turned over but would not

Turn off the solinoid. According to my diagram,

30= battery. This is going to a 30a fuse on the fuse block.

85= ground

86= key ( ignition) going from relay to the

Terminal were the starter would go.

87/87A = starter. What I'm I not understanding. #87 would just

Click while 87A would turn over but not shut off the starter after

Ignition fire.

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It should not necessary to add a relay to make the starter solenoid engage.   There is a problem with the wiring somewhere else, and this "hot start" relay is just masking the real problem.

 

If you connect a wire to the 1/4 spade terminal on the starter, with good battery cables, touching that wire to the positive battery terminal should make the starter engage, and the starter should disengage as soon as you remove the wire from the battery terminal.  EVERY time.  Check that first.

 

As far as the starter knows, the only thing the ignition switch does is connect the 1/4 spade terminal to battery positive.

 

Lets follow the power the starter solenoid normally gets, from the battery positive. 

Power from the positive battery terminal goes to the fuse block.  Depending on the year of 521, three or four fuses are always hot.  There is a white wire from the always hot side of the fuse box, to the ignition switch.  This white wire after the fuse box goes into the engine room wiring harness, and in to the cab, behind the glove box.  There are a bunch of multi pin connectors there.  The white wire then continues to the key switch, and the connector, or plug on the key switch. 

When the key is in crank position, the switch passes power to other wires, including the black wire with a yellow stripe.  This wire goes back to the connectors behind the glove box, and continues on a black wire with a yellow stripe.  That wire goes to the 1/4 spade terminal on the starter.

 

If the connectors behind the glove box have ever had water condense on them, in the last 45 years of the truck living in Oregon, there is a good possibility the connector contacts may have some corrosion on them and are not really making good contact.  A poor connection anywhere else in the chain can also reduce the current that can get to the starter solenoid.

 

If the connections and wiring that a stock Datsun uses to engage the starter needs the "hot Start relay"  chances are it will be a short time before the connection continues to deteriorate to the point it will not even make the relay switch on.

 

On a cube relay, pin 86 is coil positive, pin 85 is coil negative.  Pin 30 is usually where load, or switched fused power is applied to the relay.  Pin 87 and pin 87A  ARE different.  Pin 30 is connected to pin 87A when there is no power on the coil of the relay.  This is called "Normally Closed"  or NC connection.  Pin 87 only connects to pin 30 when power is applied to pin 86, and pin 85 is grounded.  Pin 87 is called the Normally Open, or NO connection.

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