TBI relays

[Mastiff]

My TBI setup has an aftermarket harness with two relays located near the ECM. I'm not entirely certain the function of both relays. One of them is surely the fuel pump relay. The other may just be keyed +12, so any keyed source can be used to trigger the relay and then the ECM can feed off of the same "always on" source. It's been a while, but I think the harness is only fed by a single +12 source from the battery. Does this make any kind of sense? Does the factory setup have a power relay in addition to the fuel pump relay?

 

[y5mgisi]

I THINK the second relay is for torque converter lockup, or electric fans. Tough to say though with it being aftermarket.

 

[Mastiff]

I THINK the second relay is for torque converter lockup, or electric fans. Tough to say though with it being aftermarket.

I don't think TBI (7747) ECMs did that. I know they don't control fans.

 

[y5mgisi]

Only thing i know for sure on factory th400 trucks they use the second relay for the kick down solenoid in the trans.

 

[eagle mark]

Follow the wires and find out?

But a second relay is the common way of making an aftermarket harness for these 7747 ECM. They usually go on an old points car so the wire that fed points now turns on relay and EFI system. Make sure you remove the resistor for points if it had one.

 

[Mastiff]

Follow the wires and find out?

But a second relay is the common way of making an aftermarket harness for these 7747 ECM. They usually go on an old points car so the wire that fed points now turns on relay and EFI system. Make sure you remove the resistor for points if it had one.

No points, but even so, I don't think the keyed wire to the distributor is meant to supply much current. And it probably is a one size fits all harness anyway, meant to work with points too.

 

[eagle mark]

Your right! It does not have enough power to supply what is needed. But the wire to distributor or points is what turns the relay on, it takes very little power to turn a relay on.

Look at relay wiring! It has it's own power supply wire from Batt and then power out to whatever. This is what makes it ideal to power system from a points or distributor wire!