My 1995 GMC 3500 parking lights keep blowing the fuse. I replaced the light switch/dimmer. not fixed.

What ? you looking for a magical fix . Never happen .darling . take it to a qualified repair shop. You'll never find the problem this way . Testing electrical circuits , checking for DTC'S - diagnostic trouble codes etc... is only way . You should go on the pay line .
The park, tail and marker lamps, including the license lamps, are turned on when the headlamp switch is placed in the PARK or HEAD position. The headlamp and panel dimmer switch supplies a ground signal to the BCM on the park lamps switch on signal circuit. The underhood fuse block supplies battery positive voltage to both the park lamp relay switch contacts and the park lamp coil circuit. The body control module (BCM) provides a ground or control circuit to the park lamp relay coil circuit. When the park lamps are turned on the BCM energizes the park lamp relay. Current flow is from the park lamp relay to these fuses in the body fuse block:

Would like to know what you expect to hear ,other then what i told you ? Any trained professional technician is going to tell you what i already told you . I have 30 + years working for general motors . Blown fuse means short circuit . The fuse that blows is a power supply for the BCM , the BCM supply's B+ voltage to the lighs you have not working . The BCM or the wiring is shorted .

Headlights Circuit Description
The headlights are controlled by the body control module (BCM) via the AHL Relay when the headlamp and panel dimmer switch is the AUTO position. When in the AUTO mode, the BCM receives a signal, (voltage) from the ambient light sensor, based on the voltage of the signal of n the sensor the BCM turns the day time running lamp (DRL) lights OFF and the headlights ON. The headlights can also be turned on by placing the headlamp and panel dimmer switch in the head position.
The relay coil is fed by the headlamp and panel dimmer switch or the BCM and the battery B+ buss bar in the underhood bussed electrical center (UBEC). The BCM supplies current to the relay based on the input from the ambient light sensor via CKT 352.
The relay output feeds the LT HDLP and RT HDLP fuses to supply current to the low and high beam lamps on CKT 1340 and CKT 1240. The ground for both the low and high beam lamps is supplied via CKT 524 and CKT 525 to the dimmer switch. The dimmer switch uses CKT 1850 for a ground to G203.
Some circuits are monitored by the BCM, and upon failure may set a DTC.
Park/Side Marker and Tail Lamps
The park/side marker and tail lamps are split between the following 4 fuses:
?€¢
The FR PRK

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The LR PRK

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The RR PRK

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The TRL PRK

These fuses receive voltage from the park lamp relay. When the headlamp and panel dimmer switch is in the auto position, the body control module (BCM) controls the relay by grounding CKT 1080 based on the input of the ambient light sensor. The park LPS fuse supplies battery positive voltage (B+) to the relay at all times.
When the headlamp and panel dimmer switch is in the PARK position, the relay is by passed through the INT PRK fuse. Current flows from the PARK LPS fuse through the headlamp and panel dimmer switch to the INT PRK fuse in order to feed the following fuses:
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The FR PRK

?€¢
The LR PRK

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The RR PRK

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The TRL PRK

Park Lamps Inoperative

Step

Action

Value(s)

Yes

No

1

1. Turn the ignition OFF.
2. Connect a scan tool.
3. Turn the ignition to the ON position.
4. Using the scan tool, check for any DTCs in the body control module (BCM).

Does the scan tool show any DTCs ?
--
Go to Diagnostic System Check - Body Control System in Body Control System
Go to Step 2

2

1. Turn the headlamp switch to the park position.
2. Connect a test lamp from (back probe) terminal B of the headlamp and panel dimmer switch to ground.

Does the test lamp light?
--
Go to Step 4
Go to Step 3

3

Locate and repair the open in CKT 240 (ORN) between the switch and the mid bussed electrical center (MBEC).

Is the repair complete?
--
System OK
--

4

Connect a test lamp from (back probe) terminal A of the headlamp and panel dimmer switch to ground.

Does the test lamp light?
--
Go to Step 6
Go to Step 5

5

Replace the headlamp and panel dimmer switch. Refer to Headlamp Switch Replacement .

Is the repair complete?
--
System OK
--

6

Connect a test lamp from the INT PRK fuse, located in the left bussed electrical center (LBEC), to ground.

Does the test lamp light?
--
Go to Step 7
Go to Step 8

7

Locate and repair the open in CKT 74 (LT BLU) between the MBEC and the UBEC.

Is the repair complete?
--
System OK
--

8

Locate and repair the open in CKT 74 (LT BLU) between the headlamp and the panel dimmer switch and the LBEC.

Is the repair complete?
--
System OK

Here's the link and I'm sure you will get the solution of your problem
Lancer

Same issue also when the fuse blows i looks my electric seat controls. I found the problem was underneath the hood underneath both the fuse boxes it was a power wire pinched under a plate that holds the fuse boxes on. This wire probably wore through after 140,000 miles of rubbing and being pinched. tell me if it works for you
Vehicle: 2003 impala

Does it have a trailer hitch and wiring? If so, check to make sure connector is not shorted out and double check your fuses and/or replace fuse. It may look good but I've seen some that were burned out of inspection view. You might also want to trace wiring back to brake lights, just in case snow or build up pull connectors apart.

It seems you have a sort circuit in the wiring or the switch......

normally you have 2 types of shorts, 1 is to earth and this causes the fuse to blow, indicating a fault and preventing a fire.

The second one is a short to power, where the circuit remains on, despite the switch being turned off.

I would suggest that the park light switch is shorting out.

If you are not familiar with electronics, I would prefer you seek an auto electrician to do the job.

the high beam turn signal cruise control switch in the steering column will do exactly this. we just replaced ours in our tahoe. we had only high beams also.

check the headlamp switch for a short

it may be a pinched wire that is know causing a short. the samething happened to me.

There is a ground not connected or a wire open that is causing it to blow