88 TC Tach and Ac Compressor December 31, 2008, 09:33:31 AM I am trying to finish the swap from Turbo to "408" but have run into a couple of problems. I cannot locate proper wiring that will allow AC compressor to cycle without inserting a toggle switch in line.What did you guys do to remedy the Tach situation to allow it to work with eight cylinders instead of four? I do not want to install an aftermarket tach.Any help will be greatly appreciated.Charlie Quote Selected
88 TC Tach and Ac Compressor Reply #1 – December 31, 2008, 12:11:47 PM Well the dash tach is different between the 4cyl and the 8cyl. The redline points are in different places. Also, there is a link either on coolcats or on the nato tech articles about how to convert a 4cyl tach to 8 cyl and visa vera.I have no idea about the ac part, sorry. I took a sawzall to al of my ac components. Quote Selected
88 TC Tach and Ac Compressor Reply #2 – December 31, 2008, 03:55:17 PM Eric's site does have the information needed to convert a 4 cylinder tach to an 8 cylinder. It's pretty simple, you just add a resistor.You can only convert an 87-88 tach the 85-86 units cannot be converted. The tach face on the 85-86 models are more desireable (in my opinion) as they illustrate up to 7K. Eric has the different tach faces on his site which can be down loaded and sent to a color printer it you want to fiddle with it.The accuarcy is somewhat questionable. With a little trial and error of hitting up against the rev limiter (I have an MSD AL, so I put a lower RPM chip to test it), I was able to adjust the needle to where it's pretty close.No clue on the A/C... Quote Selected
88 TC Tach and Ac Compressor Reply #3 – January 01, 2009, 04:56:11 AM Quote from: 86T-bird;249624The tach face on the 85-86 models are more desireable (in my opinion) as they illustrate up to 7K. The accuarcy is somewhat questionable. No clue on the A/C...If you swap faces very true, the mod is fairly accurate IF you retain the '87-'88 face... But the tachs weren't "dead nuts on", even in original configuration... I backwards engineered that mod, the one resistor is the ONLY electrical difference in the '88 TC & Sport tachs... If you can find a Sport tach it's a direct swap(but has no ride control LED or the boost scale)... Since my ride control is still operational, I punched a hole for the LED(I have the Sport tach in mine)...The AC compressor is controlled by the cut out relay near the front side of the passenger side strut tower... The relay gets it's control signal from the low pressure switch on the accumulator which in turn is fed from the HVAC controls... Quote Selected
88 TC Tach and Ac Compressor Reply #4 – January 01, 2009, 09:23:40 AM Thanks Guys... This will help... Quote Selected
88 TC Tach and Ac Compressor Reply #5 – January 01, 2009, 02:00:15 PM Quote from: Charles Crooks;249574I am trying to finish the swap from Turbo to "408" but have run into a couple of problems. I cannot locate proper wiring that will allow AC compressor to cycle without inserting a toggle switch in line.The Hot wire to operate the A/C clutch (LG/P) comes from the A/C- Heater function selector switch in the dash. It goes to the Clutch cycling pressure switch. The switch is mounted on top of the A/C Accumulator. The accumulator is a cylindrical can on the passenger side of the fire wall.The other wire on the pressure switch (PK/LB) would normaly go to a WOT A/C clutch cut off. On the Turbo this was a solid state circuit in the Integrated Controller Module. On a 5.0 this would be a relay.You don't really need this, especially with all the horsepower you have.You can run the PK/LB from the pressure switch directly to the A/C clutch.On the Turbo the A/C clutch got it's ground through the Integrated Controller Module. You will need to take it directly to ground.You will need the diode across the clutch to keep the pressure switch contacts from burning up.Picture coming up shortly. Quote Selected
88 TC Tach and Ac Compressor Reply #7 – January 01, 2009, 05:07:48 PM Thanks so much... Is this the same as it would be on a climate control version? Quote Selected
88 TC Tach and Ac Compressor Reply #8 – January 01, 2009, 09:34:37 PM Quote from: Charles Crooks;249748Thanks so much... Is this the same as it would be on a climate control version?Yes the wiring changes I made will stay the same.In the diagram I posted you can see the LG/P wire comes either from the manual Function Selector Switch or from the Electronic Automatic Temperature Control. Quote Selected
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