Car not starting randomly? READ THIS (30 Amp Starter Relay Mod)

Nick M

Black Rifles Matter
Authorized Seller
Sep 9, 2005
Maybe this will add some value, who knows... top problem areas:

1) Starter motor itself (bad copper contacts in starter solenoid)
I saw this often on Corollas. Then again, Toyota sells more of them than any other car maker sells of anything. Even the VW Beetle. Corollas are broken in by around 200,000 miles, then they need corrective maintenance.


Authorized Seller
Jul 23, 2012

My car sometimes did this terrible thing and ofcourse happened when i needed the most :D

It was very rare though but now after rebuild i couldnt start the car at all. So i did this "mod" for free because i have parts car - eclipse and it had a lot of 30amp relays with all the wiring attached. i just extended wires and put it on supra and sure thing - first turn of the key - wuolaaa :)

thx again. love this forum.


Regular Supramaniac
Authorized Seller
May 11, 2006
Maybe this will add some value, who knows... top problem areas:

1) Starter motor itself (bad copper contacts in starter solenoid)
2) Ignition switch
3) Pax side kick panel starter relay
4) NSW switch (A/T only)
5) bad clutch interlock switch (MT only)
6) mangled/damaged/loose starter wire connector at starter.

Use voltage drop test to troubleshoot 2-4.
Thread from the dead, but I thought it would be of some value to people still considering the relay mod (for some reason). I have been battling the intermittent no start for years but as my car generally gets under 1000 miles a year, i could never be bothered to fix it; however, I've grown tired of carrying around booster cables to start my car 1/20 times. As I didn't feel like disassembling wiring harnesses to troubleshoot with a voltmeter (and I'm shitty at it anyway), I reviewed the wiring diagram of the starter circuit (extremely simple circuit once you wrap your head around it), eliminated the low hanging fruit (bypassed clutch switch, wires and connections ok, starter rebuilt and tested), and began replacing parts. First up, the ignition switch. Problem completely solved. For $28 and 45 minutes of my time.

Fair warning, the aftermarket ignition switches from Rockauto take some finessing with a dremel to fit - they aren't quite identical to OEM.



Active Member
Authorized Seller
Jun 15, 2017
Kuala Lumpur
I had a problem with hot starts. The first cold start of the day no problem, but after the engine heats up and i shut it down and attempt to restart under 2 hours, the starter just clicks. I surmise that it is caused by heatsoak under the hood (i live in the tropics),and the 30 year old ignition barrel cable has oxidized enough that the resistance goes up when hot, and not enough current gets to the starter in such conditions. So i installed the starter relay mod, and I never had any problem starting at any time. Its been a year since I did the fix.

Jeff Lange

Staff member
Authorized Seller
Mar 29, 2005
Edmonton, Canada
The starter circuit on the car is one of the simplest circuits on the car.

I just read through this entire thread, I know it's old but I wanted to make a couple of things clear. There's a lot that goes on when you're a car owner and enthusiast. When you add to the mix that it's an old car, you've just got even more on your plate.

In my mind there are two basic things that you're going to be doing on a car like a Supra: you're going to be repairing it and you're going to be modifying it. The latter again falls into two categories, modifying it to do something it couldn't originally do, or modifying it out of necessity. The latter of those falls back into repairing the car in many cases (because the original components are no longer available, etc.).

Rewiring the fog lights so that you can use them at other times is clearly a modification to the car so that you can do something the car couldn't originally do, and there are various ways of implementing that.

Rewiring the headlights with a relay to increase the load capacity of the wiring for higher wattage lighting is again a modification to allow the car to do something it couldn't originally.

Now we get to the starter, and you want to rewire it so that it will do exactly what it did from the factory, but with a more complicated circuit (the original mod). That's not a modification, that's a repair, and unless you have a specific reason, a repair should be finding the actual problem and actually fixing it.

If you want to make the argument that you need to modify the car so that you can start it without pushing the clutch switch for some reason, that could be a perfectly valid reason to modify the starting circuit on the car. Though I would say that the modification should only be done to the extent required to make it happen. If the security system switch in your door is damaged and no longer available, and you want to remove the entire security system, so you're going to modify the starting circuit to do so, that's valid in my mind. If those things happen at the same time, and you want to remove the control relay in order to do it, sure thing.

But if you have a starting problem, and you're removing the security system and the clutch switch to fix your starting problem, that's not a modification, that's a bad repair.

These cars are old, and the wiring is likely brittle in places that get hot. I've seen it plenty of times. The wiring absolutely could be a problem. The relay absolutely could be a problem, but they're less common than other issues. When a car exhibits a problem, there are typically a number of components that could be the issue, and so there is some troubleshooting required to find the actual problem, which can then be fixed. Often on the internet, people will post a problem they're having and someone who has repaired a similar problem on their own car will chime in with "it's probably this," or "it's probably that." In some cases, the issue is so common that it's worth repeating, or it's maybe a simple place to start checking, but in many cases it's a waste of time because it's not the same car.

An example: Something that comes up frequently on newer car forums is the CEL will come on, someone will post asking "my CEL just came on, what could it be?" and people then proceed to tell them that they need a new O2 sensor. Say what? There are usually 4 of those sensors on the car, but additionally, the CEL can come on for another 2000 reasons that aren't the O2 sensor. What should that person do? As a first step, at the very least, you need to read the codes and find out why the light is on.

When you are having starting problems, should the first step be to replace the entire starting circuit with a piggy-backed relay running power directly to it? No, you should find out why the starter isn't working first.

For Denso starters, it is often the starter contacts and the plunger, but it might not be.
Some newer Toyotas have relay problems, specifically for the A/C, but the relays in the Supra aren't often a problem. But it could be.
For the wiring to the starter, it's not usually a problem, but some previous mechanic may have pulled the engine without disconnecting the starter and damaged the wire, or it may have gotten cracked from a previous engine replacement, so it could definitely be a problem.
For the connectors, the terminals could be corroded, or maybe a connector isn't plugged in all the way. It's rare, but it could be a problem.
For the ignition switch, it's pretty old now, and could be experiencing wear or corrosion and may need to be replaced.

This thread is a good example of what's wrong with a lot of the "information" available on the internet, and can be applied to countless cases of modifications being done when a repair is in order. I fully understand that some people just need their car to work, and don't have the time/skill/money, but a temporary bandaid fix to get you home shouldn't translate into a "mod" that everyone does just because.

Parts Information

MK3's came with 2 types of starters, the smaller type (1.0 kW) are much more prone to failure and do not have easily replaced contacts like the larger type (1.4 kW). When doing an engine swap using a Japanese engine (7M, 1JZ, 2JZ), use the larger starter (which is the common North American starter). Part number is 28100-46090 for the one that is a direct fit into the A70, however 28100-46140 can also be used if you swap the trigger wire connector to part number 90980-11400 and terminal/wire 82998-12480. These are the newer type of starter that are threaded and easier to remove and install than the earlier 7M starter. Denso aftermarket starters are available for both types, part number is 280-0121 for the A70 style, and 280-0163 for the A80 style.

If you are looking to repair your existing starter, contact kits can be ordered from Toyota or found online. I like the Toyota pieces, because they are full kits, but you can get away with just doing the contacts themselves if needed. These part numbers are not in the parts catalog, and are as follows:

1986-1990 Starter (Part Number 28100-45050):

28226-72080 - Battery Terminal
28226-72010 - Motor Terminal
28235-35080 - Plunger
28159-10040 - End Cover
28175-10040 - End Cover Gasket
90099-04473 - End Cover Bolts (Qty: 3)
28169-10040 - Wire Clamp

1991-2007 Starter (Part Number 28100-46090, 46140):
28226-76070 - Battery Terminal (28100-46090)
28226-22050 - Battery Terminal (28100-46140)
28226-74070 - Motor Terminal
28235-55050 - Plunger
28159-55050 - End Cover
28175-55050 - End Cover Gasket
90099-04474 - End Cover Bolts (Qty: 3)
28169-55050 - Wire Clamp

MK3's came with 2 types of ignition switch, one with 2 connectors (1986-1990) and one with a single connector (1991-1992). The earlier type are still available from Toyota for a good price (part number is 84052-22030). The newer type (part number 84450-14080) is unfortunately are no longer available from Toyota, but can be found in the aftermarket. If you are dead-set on using a Toyota part, you can use the 1986-1990 style and swap out the connectors as follows:

1986-1990 Pin1991-1992 Pin
8-pin Connector, Pin 1Pin 7
8-pin Connector, Pin 2Pin 2
8-pin Connector, Pin 3Pin 3
8-pin Connector, Pin 4Pin 4
8-pin Connector, Pin 5Pin 8
8-pin Connector, Pin 7Pin 9
8-pin Connector, Pin 8Pin 10
2-pin Connector, Pin 1Pin 1
2-pin Connector, Pin 2Pin 5

The starter relay is a pretty typical Toyota relay from the time, part number is 28300-16010 (Denso aftermarket 567-0021).

The neutral start switch is unfortunately discontinued, part number is 84540-30241. Other NSW's may work, but will likely have incorrect connectors on them.

The clutch start switch is also discontinued, part number is 84520-17020. It was used in a few cars, and others will likely be easy to retrofit if required.