ECU pig tail plug... What is it?

[Reign_Maker]

When I go to the shop tomorrow, I'll take pics of what i "think" the hac sensor is... Im just more confused now than I was... My main thing here is that this is something I DONT need for the AEM, because my AEM doesnt have that pigtail plug... And the only other plug it has is for the accesories and extra sensors...

 

[Doward]

I have ABS as well - 3 wires only, as you see in the link.

 

[zoppii]

Red - Green comes from the Turbo Indicator (whatever that is, looks like and idiot light)
Violet comes from the Defogger relay
red - yellow comes from the headlight relay.

According to Toyota wiring diagram.

 

[bigaaron]

^^^ Give the man a prize!

 

[jetjock]

zoppii got it right. One is for the turbo sensor and the other two are for idle speed control during defog and headlight operation. IIRC only 87 and 88 ECUs have the separate pigtail for those functions.

 

[Reign_Maker]

Thanks JJ... Will I need it for my AEM? Because, for some reason, I cant seem to find the extra plug that originally went to that pig tail...

 

[jetjock]

I dunno much about the AEM Jake. All the defog and headlight inputs do is control idle speed through the stock ECU. The defog input compensates for the electrical load by keeping the idle speed near the same valve while the headlight input bumps it up a few hundred rpm. I dunno if that can be done through the AEM. As for the boost gage I'm assuming you'll be going aftermarket so no worries there.

 

[bigaaron]

Headlights and defogger will only lower the idle by about 50-100 rpm max, the only thing that causes a big drop in the idle is the ac compressor, and when the engine is cold.

 

[Reign_Maker]

Ok, talk about learning something new everyday... I always thought HAC stood for "Heat/Air Conditioning", probably because Im a construction guy, haha... Well, found the TSRM on line for the pre89 and found out the HAC is for High Altitude Compensation... http://www.supra.co.nz/87tsrm/EFI/efi121.htm Now if that pig tail is for the HAC sensor, then why do I already have a plug on my HAC sensor?

 

[bigaaron]

It's not for HAC, Zoppi already nailed it on post #23

 

[Doward]

Yep, I just verified this in my own '88 TSRM - Zoppi hit the proverbial nail on the head

 

[Reign_Maker]

But I dont have an extra plug under my dash for that pig tail... Also, the AEM doesnt have a plug for that, so its just wierd... I dont think I've ever seen an ECU with the pig tail... Not that Ive seen ALOT of them, but...

 

[bigaaron]

The car will run just fine without it plugged in to anything.

 

[Reign_Maker]

Thanks Aaron...