Tow/Haul circuit access?

[Mark Rinker]

I am considering a tap to the tow/haul circuit to control main power (with a relay) to my propane injection system. My idea is to limit propane injection to towing, in addition to the MSD system controlled parameters of boost/engine temp/EGT/etc.

A benefit: If the operator forgets to turn off the propane (main switch) and shuts off the vehicle at the end of the day, the system won't be engaged again until tow/haul is engaged - typically when the vehicle/trailer is re-loaded and the operator is thinking of the load factor after securing and tarping - normally done with the truck idling and thoroughly warming up to operating temperatures.

Anyone know where to find this wire under the dash without tracing it from the indicator, or removing the steering column?

[DmaxMaverick]

It would depend on the year model you're talking about. The circuits are very different between the years. The only thing common with them is, they all have instrument panel lamps. To keep it simple, and keep out of the logic, tap the I/P lamp circuit. The T/H circuit is within the serial data, but the I/P lamp, is just a lamp, ON/OFF. If you use this, be sure to use dual series relays, micro off the lamp circuit.

[Mark Rinker]

What is a 'dual series' relay? Any particular brand or specs I should look for? Was planning on a 'Radio Shack special'.

[DmaxMaverick]

What is a 'dual series' relay? Any particular brand or specs I should look for? Was planning on a 'Radio Shack special'.

Dual relays, in series. A micro relay for the lamp circuit, then a full duty for the system switch. You don't want to put any load on the lamp circuit. Radio Shack should have the micro, and a standard automotive relay (like used for the headlamp harnesses), should work for the system switch. Make sure they are continuous duty and rated for your amp requirements.

I looked over the diagrams and it doesn't appear the T/H circuit gets outside the logic circuit, except for the lamp. The T/H switch is momentary, so that won't work for you needs. It would be very unreliable.

You could install a separate momentary switch, with a relay that would reset with an ignition cycle, and stay out of the T/H all together. This would be my choice for your situation. This would allow you to use the system in either T/H or normal, by choice.

Good luck!

[Mark Rinker]

Great idea...I'll look into the same relay control but independent from the Tow/Haul circuit.

[Racehemi]

That is exactly what EFILive's DSP

[Mark Rinker]

...

You could install a separate momentary switch, with a relay that would reset with an ignition cycle, and stay out of the T/H all together. ...

Okay, with basic electrical knowledge, I see how to wire this to enable power with a momentary pushbutton switch. By powering it from a switched power source, the circuit will reset any time the ignition is cycled. Cool enough.

However: How do you disable the same circuit with another push of the same momentary switch? This would be required for shutting off the LPG system while underway. Kinda important...

I have all the parts on my desk from Radio Shack. The MSD kit came with a simple toggle switch for main power, and one non-specific red MIL (Malfunction Indicator Light) to mount on the dash. Bor-ing, and not very informative of whats going on.

When any system parameter is inhibiting LPG flow (low water temp, low LPG pressure, under/over boost, over EGT) an amber 'caution' LED will light. When LPG is flowing, a 'green' LED will light.

Welcome RaceHemi (from the hometown of Jake and Elwood Blues...). EFI Live sounds like a great product. On of our advertisers here, John Kennedy sells those products. He has been making some great power numbers on the LLY motors.

[Racehemi]

Welcome RaceHemi (from the hometown of Jake and Elwood Blues...). EFI Live sounds like a great product. On of our advertisers here, John Kennedy sells those products. He has been making some great power numbers on the LLY motors.


Thanks for the welcome however I've been here almost 5 years, just changed my nickname after the server upgrade. I own EFILive and I'm running a couple of John Kennedy's tunes(150 & 190hp) based on EfiLive's DSP2 Operating System. They are strong, smooth, consistent, low smoke, low EGT's, great trans shifting, big on power and throttle response. I highly recommend them and would forget the relay thing, give John a call and have him set you up with one of his tunes, you won't be dissapointed!

The best part is that he can build you a custom tune to fit you and your needs.

[Mark Rinker]

John...is that you???