Tom wrote to us saying that he is having trouble with an intermittent no-start issue with his 1990 model Toyota truck and from what he has written it sounds like either the contacts in the starter solenoid are worn or there is a current drop issue from the battery to the starter. On occasion the factory starter relay can be heard clicking when the key is turned but nothing is happening at the starter motor.
What we are going to look at today is fitting an auxiliary relay to the starter motor circuit in an attempt to overcome this no-start issue. While I have seen this ‘trick’ solve these types of problems on numerous occasions it is definitely not an answer to all starter problems. For example, if the solenoid contacts are completely worn out or the starter is otherwise past it’s use-by date it is going to do very little but I think it’s worth a go if you have intermittent problems such as what Tom is experiencing.
Basically the use of a relay allows the battery’s full current to reach the solenoid. Check out my dodgy diagrams below for a basic idea of how it works.
Basic Starter Diagram Without Relay
Basic Starter Diagram With Auxiliary Relay Fitted
NOTE – Some auto parts stores and auto electricians will have a pre-wired relay setup if you don’t want to go through setting one up yourself.
Ok, let’s take a look at what you will need to get this operational.
- One 4 pin – 30 amp (minimum) Relay
- 5 insulated Female Blade connectors
- 1 Male Blade connector
- 2 ‘Ring’ type connectors (1 large, 1 small)
- 4 lengths Electrical wire – more on the wire in a moment.
The first thing we need to do is take a look at the relay and identify the four different pins. They should be numbered on the underside of the relay box with 30, 87, 85 and 86. If you’ve fluked it for a five pin relay there will also be 87a, that’s ok, that pin won’t be used.