Third Generation F-Body Message Boards - Electronics

87 iroc fuelpump wiring

Jari79 — Thu, 16 Apr 2026 16:39:09 GMT

Hi, could somebody tell me is my Haynes wiring diagram correct or not. I have seen different wirings to fuel pump. This shows that oil pressure switch would cut off fuel pump electricity even relay is working.
Another schematics i have seen that relay and switch is connected pareller.
So witch one is correct or is there mnay different versions of wiring?

Passenger fenderwell connector removal

SteveC68 — Thu, 16 Apr 2026 03:33:24 GMT

How do you remove the connector that is behind the fender liner on the passenger side of the car? This is on a 1989 IROC. I tried to spread the locking tabs but it didn't want to budge. Are those tabs the only thing holding it on?

No crank no start

Zachthalen1 — Thu, 16 Apr 2026 02:06:32 GMT

Just put the battery back in my 85 sport coupe trying to get it back on the road for the summer. I tried starting in and it wouldn�t even turn over. The car ran fine before the battery came out for the winter. I checked for voltage and there is power going into the ignition switch but there doesn�t seem like there is voltage to the wires going to the neutral safety switch. Basically I�m just looking to see if I�m on the right track or if I am missing something

Brake Light issue

magicdave2 — Wed, 08 Apr 2026 20:30:23 GMT

I don�t have any brake lights on my 1983 Trans Am Recaro. The fuse panel for the brake lights has 12v when I back probe it but there is not power at the brake switch. I have added 12v power to the switch wiring and the lights come on so everything from the switch backwards seems to have continuity. Where should I look if I am losing power between the fuse and the switch? Thanks!

Gauge cluster motors / resistors

Aussie3rdGen — Wed, 08 Apr 2026 07:30:14 GMT

G'Day everyone, Happy Easter.

For some clarity before I start asking questions.
Vehicle: 88' Trans Am - 305 TPI - Analog gauge cluster.

I need some guidance as to which gauge gets which motor/resistor. I have attached photos below of the motors/resistors I'm referring to (please tell me the correct name if I'm getting it wrong).
For example, does the fuel gauge get a motor that has 2 resistors on it or one? Same question for Oil temp, Pressure, Coolant Temp etc.

Second question:
At the moment, with the key in the ON Position, the Fuel gauge is maxing out to EMPTY. The Coolant temp and Pressure max out to HIGH.
I've checked the grounds on the C1 and C2 instrument panel connectors; they have good grounds. I have tested the continuity on the printed circuit board on all the circuits, and they are all fine. So I believe it's not just a simple grounding issue?
especially as 3 gauges are on the fritz! Which leads me to believe the motors driving each of the gauges may be incorrect, and the resistors aren't regulating the current correctly?

Speedometer wiring from PCM

upstateRich — Tue, 07 Apr 2026 00:37:01 GMT

I have a PSI harness that I am using for my PCM and my question is can I run the black wire from the harness directly to the speedometer the directions are saying that it is 4000 pulse per mile. Is it true that a it would require a inline resistor to pull up the signal?

Instrument cluster connector terminals

dannyual320 — Fri, 03 Apr 2026 04:16:08 GMT

I've got a 1987 IROC that I'm installing a Holley 12.3" ProDash into. I need some of the inputs to the stock instrument cluster such as the blinkers, headlight high beam and fuel level. Here are some pictures of of the connectors and terminals:

You can see that I've depinned some of the terminals.

These wires are not long enough to reach my connector that plugs into the back of the ProDash. I know that I should just cut off the copper terminals and splice a new piece of wire on. However, the **** in me would rather not cut the OEM terminals off. Are there any metal terminals available that would mate up with the individual copper terminals shown above? If not, I guess I'll just have to cut the copper terminals off.

Diode dynamics bulbs

thatsupnow — Thu, 02 Apr 2026 23:14:43 GMT

Hey guys anybody here by chance happens to know what part numbers I'd need for marker, taillight, and reverse bulbs from diode dynamics?? Thanks guys

Digital dash need help

george88gta — Wed, 01 Apr 2026 04:15:59 GMT

So I just had a brand new 383 with the Holly Terminator X put in my 88 GTA. Well he was doing it I had him swap my steering column to another one that I already owned in better shape also had a company refresh the tranny at the same time.
when I went to pick up the car I had no lights on the digital dash. He said oh sometimes they go bad there are companies that fix them but the truth of the matter is I knew it was from the install.
at first I thought maybe it was because of the steering column because when I click the key forward a tiny bit the dash would lightly light up and I would see a couple of the gauges on voltage move up the chart, it would also lightly light up in the accessory position but nothing in the Run position ( the only thing that does seem to work is the system check which I believe is totally separate).
I checked the power of the ignition switch 12 volts and then removed the gauge fuse and tested there for 12 volts, all good. That's when I realized with the fuse out and the and auxiliary position I was still getting a dim light and see the needle moving on the digital voltage.
how is it possible that the gauges will even work with fuse out?( I think I do remember by touching the key somewhat in the past that I could get the gauges to climb above what was actually reading on the gauges maybe this is something normal in between key positions.)
so the only way that I could think of the gauges doing that with a fuse out is if it's a ground fault and back feeding. Is there anybody who has knowledge of this system and can help pinpoint me in where my problem would like considering the typical things that were touched on the car during a holly install. I've never had a problem with the digital dash before.

And to spend all this money and get the car back with no gas gauge tachometer mileage speed has me pretty defeated. Thanks in advance hopefully in 2026 good people lurking around these boards

digital dash pod circuit board

mjmp — Mon, 30 Mar 2026 18:21:28 GMT

Hey all! Just picked up an 84 Berlinetta with the starship interior. I am having some troubles regarding the turn signals. I opened up the pod to take a look and a couple of these metals pop up switches have severed. What do I call them to find some to buy? I have tried reverse image searching and yielded no results. Any help at all would be appreciated.

Gauge Cluster Issues/No Charging

praterjason — Mon, 30 Mar 2026 17:27:15 GMT

Having an Issue with my 88 Formula, Battery is new and Tested, New alternator, tested as well. Volt gauge always reads below 8, and the battery will die if i drive it more than 10 minutes. Anyone know what next steps may be. Car had set for many years, but ran when I parked it while in service before I could get it painted and interior redone. Never did remove the engine. So at a loss right now.

Can anyone tell me what this connector is?

GearheadSS — Mon, 30 Mar 2026 13:24:46 GMT

86 LG4. I bumped it while replacing heater hoses and it broke the tab because it's super brittle. Trying to see if I can find a new one.

Digital dash

george88gta — Sat, 28 Mar 2026 21:34:37 GMT

Just got car back from New motor and holly computer being installed, my digital dash is Now not working can anyone point me in the right direction on what and where to look at everything is hooked up to my original gauges. The info check is working just nothing else

Computer to be removed

dwwebste — Fri, 27 Mar 2026 22:35:45 GMT

Question about wiring: quite sure I've been told that for an LS swap the wiring harness that comes from the computer through the firewall is not needed and can be removed. What are the wires here (circled in red) attached to the side of the computer? I would rather not cut wires just in case something is needed but want a cleaner look as well. Pics also show where wires go through the firewall. In the engine bat, the wire circled in green just has a clip on the end, but it traces back to the driver's side so I'm not quite sure what to make of that.

Thank you!!!

Wiring harness identification

metalhead8711 — Thu, 26 Mar 2026 04:43:58 GMT

Hello everyone. I have a 1989 pontiac firebird trans am gta convertible. I've recently purchased the stock shifter assembly and neutral safety switch wiring harness to undo the previous owner hack job. Wiring harness was chopped off before ashtray and they installed a b&m shifter but it wasn't wired correctly and im getting alot of electrical gremlins. My power windows and mirrors dont work but the harnesses are getting power. The hatch release switch is not working. Not sure what it's supposed to do on a convertible but neither the trunk not the tonneau are releasing. Not even a relay click is audible. Im hoping installing the removed harness back might solve some of those woes but there's a certain bundle towards the rear I cannot identify. This rear bundle has 2 black wires. 1 orange. 1 gray and a brown or tan wire with a white stripe that has a peculiar connector. I did my best to identify the rest of the bundles. Any help would be appreciated. My chilton manual makes them a little difficult to decode.