Auto Electrical Forum
Automotive Electrical Tech Tips and Questions Answered

LED turn signals not flashing.

     Posted on Tue ,06/07/2010 by benevolent dictator
Hi, I’m trying to replace the bulbs (incandescent) on my motorbike’s turn signals with orange LEDs. I calculated the resistance of connecting 2 LEDs in series and sourced a resistor to attach, supposedly to replicate the same load as the OEM bulbs, problem is, when I test it the LED’s light up but just stay on constantly rather than flashing like they should.
I’ve tried numerous configurations to see where Im going wrong but the only results I can get are as described above, or not lighting up at all.
Here is my calculations taken from led calculator
Power Supply: 12V
LED voltage drop: 2.2V
LEd current rating: 75mA
Number of LEDs: 2 in series
And it says I need a 110 ohm resistor on the ground side of the LEDs.
Which is exactly what I’ve done.
Where did it all go wrong?
The simple answer is the voltage drop, two LED’s will not have a 2.2 volt drop.
But let back up and look at the big picture here. Normally an automotive turn signal system will use 2 to 4 bulbs per side, lets focus on a 2 bulb system. The most common bulb is the 1157 which has about 20 watts on the bright side per bulb for a total of 40 watts per side, this is the wattage that the flasher will “see”. Now if we use the calculator on we will find that we need to replicate the following;
we will need 3.33 amps with a resistance value of 3.6 ohms.
Now as I read the question it seems you are trying to run the power through the flasher to one led to the next led and then to ground. This a bit awkward, a better way to run this would be through the flasher then run one wire forward and one wire back, after each led then install two relays, one at the front and one at the rear. This would require a pair of 3 to 4 ohm resistor however you are going to need about 25 watts per led. This will get warm so you would want to use the resistors with a built in heatsink or one designed for automotive use. They cost around $10.00 or you can just buy a flasher designed for use with leds, they are know as electronic flashers or led flashers. In my opinion the electronic flasher is an easier way to go, but both should get your turn signals flashing again.

fuel pump wiring with fuel injected engine swaps?

     Posted on Mon ,26/04/2010 by benevolent dictator

Jim Asks:
I have a modified 1987 Fiero GT.
It had a 1995 Cadillac 4.6 Northstar in it.

Fuel connector C502 in the center rear engine bay, connects to fuel tank.
Has a pink wire, a tan/white, and a black wire.
I have added a external fuel pump.
I’m ready to start motor up.
The C502 connector, shows volts when key is on.
(Fear blowing up car.)
The tan/wht wire is for the fuel pump,
which I have elimamated.
Should show voltage?
Question: should that C502 connector show voltage?
Thanks Jim

I think this is something that others may have an interest in, so I am going to frame my answer in a generic form.
When doing an engine swap there are many things that must be accounted for in regards to fuel injection. You are most likely going to use the ECU or a modified ECU for the engine you are swapping into the vehicle. Now lets look at the obvious, the fuel lines should be the same size, keep in mind we need to move the same volume of fuel not just the same fuel pressure.
Next does the new engine have a fuel pump control module or is it a simple relay control. If it is a relay design then the wiring is easy, just replicate the wiring and you are ready to do. If the new ECU has a fuel pump control circuit, internal or external, it must be inspected carefully. You can just wire it in because it may have “G” sensor circuitry, this will adjust pressure based on what the vehicle is doing, keep in mind a Cadillac will not corner the same as a Fiero. A mistake here can cause over rich or lean out during cornering or under accretion or deceleration. You may be better eliminating the controller and this will require duplicating the ECU inputs so the ECU will not trip a code or go into “limp home”.
This is how I normally wire it in, step one check the wiring to determine if the ECU controls ground or voltage. Most ECU’s supply the ground for the fuel pump and the voltage is supplied when the key is turned on. To play it safe I will run a relay, the ECU controls the low current side and the battery supplies voltage to the fuel pump and ground is run through the relay.
Finally make sure your fuel pump can make the specs of the engine you are swapping in. Now a hot tip, if this is a daily driver with some part time racing, check out our adjustable external regulator. With this you can run 14 volts when not racing but turn the voltage up to 16 – 17 volts when racing, the fuel pump will supply all the fuel you will ever need at 16.5 volts. We have seen .5 sec to a full second gain in the quarter mile.

Will an automotive electric fan run on ac power?

     Posted on Mon ,26/04/2010 by benevolent dictator

Jeffro Asks:
Can I run some radiator fans from a Nissan Primera on AC power?
I want to use them in a heat transfer system in my house.

The simple and easy answer is no, however you can purchase a 12 volt power supply to convert ac power to dc and that will power the fan, however I think it would be more cost effective to purchase a ac fan.

Jake needs to wire a convertible top

     Posted on Mon ,05/04/2010 by benevolent dictator

Jake asked:
hi guys im from Australia and need to rewire my roof for my s13 convertible due to a fire.
Basically it has a motor in the rear boot with hydraulic oil which drives the hydraulic arms to open or close roof.
there’s a +/- wire on motor, at the moment I just use car battery terminals +/- to open roof. how can I wire a switch in cabin?_any assistance will be great, I have a 3 way switch, will I need a relay? fuse? run power from where?
thanks Jake

most all motor circuits work the same regardless of if it is a window motor, door lock motor, or a top. Of course newer vehicles are more complicated, many are controlled by the body control module and cant be easily bypass.

By way of review the system works like this; push the switch one way and the top goes up, push it the other way it goes down. The big question is amperage, something like a hydraulic motor will require around 30 amps, compared to a door lock motor that will only be around 10 amps. So for this problem you are going to need a switch that can handle 30 amps, however that may not be the most attractive switch in your interior.

The answer here is a low current switch and 2 relays. Now the easiest way to do this is to order a switch relay kit, it gives you everything you need to make the system work and allows you to run your own switch. If you would like to order one contact our sales department here

If you want to wire it your self here is the layout of the two relays. tape 2 relays together, on the pin side wire the connections as follows:

pin # 85 from one relay, pin #86 on the other relay, and pins #87 on both relays will connect to a 12 volt source using 10 or 12 gauge cable, be sure to use a 30 amp inline fuse and attach the power directly to the battery.

pins # 87a on both relays connect to ground,

the switch should be wired with grounds, the center pin will go to constant ground and the up and down leads will go the relays

ground input from the switch will go the pin #86 of one relay and pin #85 on the other relay, this is low current os you can wire this with 16 gauge wire.

Pin #30 of one relay will go the black wire of the motor and pin #30 of the other relay will go to the red wire of the motor.

Now when you push the switch up or down you should hear a click, this is normal. You may notice the switch is working backwards, that is you push up and it goes down. Just switch the leads at the switch or pin #30 on the relays.

Fuel Gauge Problem

     Posted on Fri ,02/04/2010 by benevolent dictator

Robert asks:

having a problem with my gauges the fuel gauge pegs all the way past full when key is on. and I have no voltage. fuel has 2 tanks and wont switch over . this is a 89 ford f250 7.3 can some one tell me were I might be able to start to look for the problem


First lets cover the basic operation of the fuel gauge, this is not all of them since newer vehicles are handled by the Body Control Module (BCM), however we need a background for the operation.

In the gas tank there is a float that is attached to a rod, which moves a pointer along a resistor, a ground signal is sent across the resistor and then to the gauge, the resistor limits the ground that goes to the gauge, more resistance = less gauge movement, or less gas in the tank.

Now hopefully we are talking about a factory installed tank switch, if this is the case you will be able to find wiring diagrams to trace the wiring. If the switch is a aftermarket switch then you will need to contact the manufacture for wiring information.

If it seems I am concentrating on the switch it is because I am, with wiring always go with the most logical problem. In your question you mention that the tanks will not switch over, in most designs the switch also controls which fuel gauge is sending a signal to the gauge. So I would start with testing the inputs and outputs of the switch wiring and replacing the switch if it is bad. But again you will need to know what type of system you have.

You may want to stat at the dealer parts house, give them your vin number and see if you truck had factory installed dual tanks or aftermarket.

If it turns out that the switch is not the problem I would next check the GEM module, it is bit like a early BCM. The GEM is a fairly common item to fail on Ford products and finally the gauge could be bad, check all fuses and follow the wiring diagram.

This is a good time to announce a new service we are offering, finding wiring diagrams is difficult enough but then how do you read them? We now offer personalized wiring diagrams, pricing ranges from $39.95 to $99.95 depending on the problem and vehicle. You would receive a diagram of the circuit, what each wire color voltage should be, and how you can find the wire on your vehicle. So you need a volt meter but hey for less than an hour at the dealer you could fix your electrical problems. To get yours just send a note to

Now one final note, when working on wiring on newer vehicles never use a clamp on test light, you must use a volt/ohm meter. Test lights send too much voltage through the wiring and can damage electrical components.

A question about GM gauges with power when the key is off

     Posted on Mon ,15/03/2010 by benevolent dictator




This is a great questions because it gives me a chance to make a very good point, which is some times it is best to bite the bullet and pay the dealer for an hour labor. But let’s look at the problem first. The likely problems here are as follows, 1) Body Control Module (BCM), 2) key switch or 3) you have added an aftermarket alarm/remote start and it has a problem.

You have 2 choices for the BCM, first unhook the battery for about an hour, I know that most manuals say 5 minutes but lets just make sure the BCM resets. If resetting the BCM fixes your problem you will need to replace the BCM because it is probably a glitch in the system and it will probably start doing it again. Second choice is take it to the dealer and have them test it, the sad fact is the auto parts store and inexpensive OBD scan tools will not read or program the BCM, also it is important to note that if you need to replace the BCM it will need to be flashed by the dealer.

You could have a problem with the key switch, but I don’t think so, I would start with the BCM and the dealer can easily tell if it is the BCM or the key switch.

The alarm is easy to diagnose, if you have one look under the dash, look up near your foot pedals. You are looking for a black box (brain) which has several wires leading from it, about 2″ to 5″ our from the brain you will find some fuses, if the harness is taped find a square part of the tape, remove the tape and you will see the fuses, remove all fuses and see if it fixes your problem. If so you will need to consult a local stereo shop.

If you have bought this as a used vehicle you may have an alarm without knowing it, some times they are just left installed and “dormant” this is a bad idea because if the alarm fails it can result in the problems you are describing. If you don’t want an alarm or want to have it removed it is ok to leave it installed with the fuses removed, however some alarms interface with the key switch wiring preventing it from starting with the fuses installed, if this is the case with yours, then install the fuses and drive it to your local stereo shop and have them remove the alarm.

Jeep CJ Steering Column Swap

     Posted on Mon ,08/02/2010 by admin

OK I am 6′2″ and 250 LB so an 80 JC5 was probably a dumb purchase, but hey I love to tinker. My solution? Swap in a pre-air bag, early 90’s XJ/MJ steering column is a real easy swap.
I grabbed a tilt column from a 92′, it will bolt to the upper column mount bracket, the turn wiring is the same as many 70’s and up CJ’s so that may be a plug and play or at least it is easy to rewire. You can grab the control module and use the intermittent wiper on the column and if you find one with cruse control it is a great way to kick on a radiator mister or….what the hell a nos switch! Anyway here is the changes that are needed, cut off the lower mounting flange on the 92 column, cut 1″ off the bottom of the shaft and grind a new groove for the steering joint bolt. If your column has ignition in the column the plugs should be the same depending on the years, however I found that my brake pedal hit my IG switch, easy fix is to shim the column down at the fire wall about 1/8″ or so. Oh you can also move the dimmer switch to the one in the column as well.

1) Old column ignition switch.

2. New column ignition  switch, both are a GM base so they should be interchangeable. A quick check in a wiring diagram will tell you.

3 Old column turn switch plug
4. New column turn switch plug. 99.9999% chance you will have a standard GM plug here, depending on the year of your vehicle of course.
5. Connection for column dimmer switch. Easy to modify your wiring to move the dimmer to the column
6. Difference in shaft original shaft about 1″ shorter
7. How much needs to be cut off.
8. Cut a grove for the steering shaft bolt.
9. I just used a grinder to make the cut, easy could have done all this with a hacksaw and a Dremel. Now in photo #8 you can see the grind marks on the column tube, this the place the mounting flange was. I cheated here because I had my alternator bracket fabricator cut this with a plasma cutter. I am sure it could be done with hand tools or home power tools but on the other hand I would not think a machine shop would charge that much for this to be done.
Now it’s a different ignition switch but only because it is a tilt, for the most part Jeep uses a GM column with one of two ignition switches depending on if it is a tilt or not. The plugs for the most part are universal. So if you go non-tilt to newer non-tilt you may just be a plug and play deal. However that negates the real advantage of this swap, the tilt column. Older switches have less ignition lines (ignition 1, ignition 2 and so on), if you add a lot of accessories you can power them off the additional ignition wire providing you get the wiring plug with the column, just be sure to check the wiring diagram to verify colors.

For the most part your column ignition switch should be interchangeable, keep in mind I am talking about going from late 70’s – mid 80’ to late 80’s – mid 90’s column. I did have a slight clearance problem with the brake pedal hitting the ignition switch but a minor adjustment to the switch fixed this.
The dimmer switch is a cake walk, just plug it in to the dimmer on the column, you will notice a 4th pin on the switch, don’t worry about it you will not need it.
Now the fun part, I used my stock wiper switch to control my aftermarket driving lights, the switch is designed to handle some high current so as long as you are using less than 4 lights or so you should be ok without a relay just be sure to run a new power wire to it and fuse it. Since the switch is a high / low I set it up to run 2 lights on at the low position and all 4 lights on at the high position. You will want to re route the factory wiper motor wire to the column switch. To take full advantage of the column wiper switch you really need a 4 wire wiper motor, they are a bolt in interchange, just need to wire it up. Keep in mind you need the wiper module from the XJ or you need to use relays for the motor, the switch is not designed to handle the amperage of the motor. Simply check the wiring diagram and you will see the wires you need to use.
As you probably notice I am not going into wiring colors here, Jeep did chance them over the years so I thought I would just leave you to look up if you decide to do the swap. However if the diagram makes not since to you just send me a note ( telling me the year of your CJ and the year of the column

old plug
new plug
Intermittent wiper control box
column installed

New dimmer (light brown), just like the old dimmer next to it, top center pin is power in. two pins below it are high and low, 4th pin on bottom is not used.

ignition switch, notice how close the brake is (near the spring)

This is the factory wiring attached to the wiper module, you could just use relays here and it would work just fine. I used the 3 wire motor here and it will work o.k. but it is much better with the 4 wire motor. I wired the 3 motor to test the module during the time I was waiting for the 4 wire to arrive.

The best alternator swap for your CJ with a GM alternator.

     Posted on Mon ,08/02/2010 by admin

Why a CJ? They are cool, that is why!

In the early days of the Buick Park Ave GM had a problem, they needed much more power at low rpm, the answer was to build a CS-130D alternator with a very unique mounting pattern. This was only done for a couple years because it was replaced with a CS-144 which is larger than the CS130D, in fact so large that it would present a mounting problem in the CJ with the factory GM 12SI alternator. It’s more open than the original alternator to allow better cooling but its slip ring and bearings are better protected from dust and moisture. It can be built to 250 amps as well as converted to external regulated as see here, however you will need to convert to a multi-ribbed belt if going over 200 amps, smaller pulley gives you better power at idle when used whit a high amp. Wiring is easy due to an adapter plug, you would need to go with a larger cable from the battery to the alternator battery post, and get rid of your junk fusible link, use a blade fuse.

But there is always a catch, GM phased this unit out, so for the most part you can only get it at custom builders, like say Rush Power Systems for example (Rush Power Systems -Free shipping on high amp alternators and other automotive electrical products) some shops may still have this unit just be careful not to get the CS130, it should not have an external fan, if it does you have the 130 and not 130D

The main advantage here is the fact that you get much better power at an idle and low RPM, for example the stock CS130 alternator is 105 amps and can produce up to 60 amps at an idle, the stock unit produces 60 amps at 4000 engine RPM. More power is better because the lights are brighter, heater blows more air, ignition is more efficient, and it is a must if you are going to run fuel injection.

Installed CS130D 200 amp alternator in 258 Jeep CJ

Auto Electrical Tips and Your Questions Answered.

     Posted on Thu ,21/01/2010 by admin

Did you ever wish you had a place to go to ask auto electrical questions? Ever wish you had a place to go for automotive electrical tips and tricks? Well here it is, The Auto Electrical Forum is the place to go to have your auto electrical questions answered as well as pick up great tips and ideas. The Auto Electrical Forum is a joint effort between Rush Power Systems and it owner Darren Flint, with over 25 years in automotive electrical experience, specializing in high output alternators and custom built charging systems as well as wiring harness design and repair. Now you have the knowledge to repair your electrical systems at your finger tips. Got a question? Ask it, want to make a comment? Please do, need more info? Want to add something to it? We encourage it.

This site is actually a bit of a sister site to The National Voltage Star, for many years TNVS covered all automotive aspects of automotive electrical customizing and repair, and is going to now focus on the street rod / hot rod end of customizing and repair. So feel free to join one or join both, we are here to help.if you are helped out feel free to tip us using the donations link. Only issue we have is this, you spam you are out! Thanks and enjoy.